1. The Na+-K+-ATPase, or sodium pump, is the membrane-bound enzyme that maintains
the Na+ and K+ gradients across the plasma membrane of animal cells. Because of its
importance in many basic and specialized cellular functions, this enzyme must be able
to adapt to changing cellular and physiological stimuli. This review presents an
overview of the many mechanisms in place to regulate sodium pump activity in a
tissue-specific manner. These mechanisms include regulation by substrates,
membrane-associated components such as cytoskeletal elements and the γ-subunit,
and circulating endogenous inhibitors as well as a variety of hormones, including
corticosteroids, peptide hormones, and catecholamines. In addition, the review
considers the effects of a range of specific intracellular signaling pathways involved
in the regulation of pump activity and subcellular distribution, with particular
consideration given to the effects of protein kinases and phosphatases.
in 1997, the Nobel Prize in Chemistry was shared by Danish researcher Jens C. Skou
for his discovery of the Na+-K+-ATPase. Although the existence of an active “sodium
pump” had been previously hypothesized, Skou was the first to suggest, in 1957, a
link between transport of Na+ and K+ across the plasma membrane and a Na+- and K+activated ATPase activity (307). The significance of this discovery is underscored by
the subsequent publication, each year, of scores of reports relevant to various aspects
of Na+-K+-ATPase structure and function. Although much information about the
enzyme has become available in the years since its discovery, one area of pump
research that is not completely understood, despite recent advances, is that of pump
regulation.
The basic function of the Na+-K+-ATPase, or sodium pump, is to maintain the high
Na+ and K+gradients across the plasma membrane of animal cells. In particular, the
sodium pump is the major determinant of cytoplasmic Na+. As such, it has an
important role in regulating cell volume, cytoplasmic pH and Ca2+ levels through the
Na+/H+ and Na+/Ca2+exchangers, respectively, and in driving a variety of secondary
transport processes such as Na+-dependent glucose and amino acid transport. The
sodium pump, in turn, is the target of multiple regulatory mechanisms activated in
response to changing cellular requirements. The requirement for modulators of the
Na+-K+-ATPase is likely to be greatest in tissues in which perturbations of the
intracellular alkali cation content underlie their specialized functions, in addition to
those processes mentioned above (see below for specific references). Prime examples
are the changes in sodium pump activity that occur in response to physiological
stimuli such as nerve impulse propagation, exercise, and changes in diet. Expression
of various isoforms of the sodium pump may fulfill some of the requirements for
altered pump behavior (for recent discussion, see Ref. 42). However, direct tissuespecific modulation of the enzyme also underlies mechanisms of pump regulation.
One of the primary needs for sodium pump adaptation comes from changes in dietary
Na+ and K+. The mediators of natriuresis and diuresis, namely, hormones that control
the volume and ionic composition of blood and urine, often act directly on the sodium
pump of the kidney and intestine. The function of the pump in absorption or
reabsorption of Na+ and K+ and, secondarily, other solutes, requires tight regulation of
the enzyme to maintain normal levels of Na+ and K+ during altered salt intake (for
reviews, see Refs. 101, 160). In addition, because water and Na+ transport across
epithelia are invariably linked, the work of the sodium pump is also critical to water
absorption in the intestine and reabsorption in the kidney. Illustrating this are reports

2. that impairment of the sodium pump in kidney and small intestine can be associated
with the pathophysiology of hypertension (168) and chronic diarrhea (123),
respectively.
In excitable tissues such as neurons (141), skeletal muscle cells (82), and pacemaker
fibers of the heart (320), the sodium pump must reestablish the electrical potential
across the plasma membrane following excitation-induced depolarization. Although
part of this function is undoubtedly fulfilled by the presence and distinct kinetics of
the α3-isoform in neurons, regulatory events are also likely to be involved as
evidenced by the multiple effects of various hormones on Na+-K+-ATPase activity in
these tissues. In skeletal muscle, regulation of sodium pump activity has widespread
physiological implications. Continuous stimulation of muscle fibers during exercise
leads to dissipation of the cation gradient necessary for muscle contraction. To offset
excessive release of K+from the muscle cells, rapid activation of Na+-K+-ATPase
activity under these conditions is an essential means of delaying the onset of muscular
fatigue and reducing potentially toxic levels of plasma K+.
Na+-K+-ATPase regulation in cardiac muscle is particularly critical to the
myocardium, where the enzyme acts as an indirect regulator of contraction (45). Thus
the sodium pump controls the steady-state cytoplasmic Na+concentration, which then
determines Ca2+ concentration via the Na+/Ca2+ exchanger. Ca2+, in turn, is pumped
into the sarcoplasmic reticulum (SR) by the sarco(endo)plasmic reticulum calcium
(SERCA) pumps. Regulation of the sodium pump in these tissues is therefore
paramount for determining the “set point” for cardiac muscle contraction and the
steady-state contraction of vascular smooth muscle. Physiological regulators that act
in a manner analogous to that ascribed to cardiac glycoside inhibitors of the Na+-K+ATPase are likely to be critical for normal heart contraction. The aforementioned
mechanism of increasing the force of contraction via increasing cell Na+ is considered
to be the basis of digitalis therapy for cardiac insufficiency (329).
This monograph focuses on mechanisms of tissue-specific regulation of the sodium
pump, with emphasis on two areas. One deals with mechanisms involving signaling
pathways that result in modulations in pump activity, and the other deals with the
regulation resulting from the interaction of the pump complex with other membrane
components, which, in turn, may or may not be subject to modulation via other
signaling cascades.
SUBSTRATE CONCENTRATIONS AS
DETERMINANTS OF PUMP ACTIVITY
The simplest and most straightforward determinants of pump activity are the
concentrations of substrates. The sodium pump is activated by Na+ and ATP at
cytoplasmic sites and by K+ at extracellular sites. The most dramatic effects involve
variations in cytoplasmic Na+ concentration. Half-maximal activation of the enzyme
by intracellular Na+occurs at concentrations of ∼10–40 mM, which, depending on the
tissue, are often at or above the steady-state Na+concentration (for example, see Ref.
309). Accordingly, small changes in the cytoplasmic Na+ concentration secondary to
activation of either various Na+-dependent transporters or Na+ channels can have
dramatic effects on sodium pump activity. As described below, some hormones

3. appear to alter sodium pump activity by changing its apparent affinity for Na+ (KNa′).
Aside from its direct effects on the Na+-K+-ATPase, Na+ has been shown to induce
other mechanisms of upregulation of the sodium pump. For example, Na+ influx is
thought to be the first signal leading to an increase in surface sodium pumps in one
kind of aldosterone-mediated short-term regulation (302).
Whereas the high affinity of the enzyme for K+ at activating sites generally precludes
an effect of variations in extracellular K+ concentrations on sodium pump activity
except, perhaps, in some neuronal tissues (318), K+ has been shown to act as a
competitive inhibitor of Na+ binding at cytoplasmic sites (134). Therefore, variation
in cytoplasmic K+ concentration, or, more likely, in the affinity of the enzyme for K+
as an antagonist at cytoplasmic Na+-activating binding sites, is a plausible mechanism
for determining the set point for the physiological concentration at half-maximal
activation (K0.5) for cytoplasmic Na+activation (327).
Because the K0.5 of the Na+-K+-ATPase for ATP is between 300 and 800 mM (310),
the ATP concentration in most cells is saturating for the enzyme. However, in some
tissues and under certain conditions, ATP levels may fall to subsaturating levels. For
example, cells of the kidney medulla are known to function under near anoxic
conditions (56), and such conditions can lead to dramatic drops in ATP levels (310).
Thus variations in ATP concentration or in the affinity of the sodium pump for ATP
may be physiologically relevant mechanisms of pump regulation in this tissue.
MEMBRANE-ASSOCIATED COMPONENTS
Because the Na+-K+-ATPase is a membrane-embedded protein, the nature of
constituents comprising the membrane components should be an important
determinant of enzyme function. Unfortunately, this is an unclear aspect of pump
research due mainly to the difficulty in separating such components from the enzyme
complex. As a first step toward gaining some insight into the question of whether and
to what extent tissue- rather than isoform-specific differences in kinetic pump
behavior reflect pump modulation by components of the membrane, Munzer and coworkers (240,241) examined the kinetic behavior of kidney pumps delivered by
polyethylene glycol-mediated fusion into another (red blood cell) environment. In the
case of pumps incorporated into genetically low-K+ (LK) red blood cells, they
obtained unequivocal evidence of kinetic changes effected by the Lpantigen of these
red cells (see below; Ref. 353). Using the same membrane fusion system, Therien and
Blostein (324) recently showed that the membrane environment has highly specific
effects on the interaction of kidney pumps with Na+ and K+ on the cytoplasmic side;
specifically, fusion of kidney pumps into dog red blood cells abrogates, at least partly,
the relatively high susceptibility of kidney α1 pumps to K+/Na+ antagonism at
cytoplasmic cation activation sites.
In general, there is little information on the nature and mechanistic basis of sodium
pump modulation by specific membrane components. Many reports have focused on
the role of membrane lipids. The main effects of lipids on the sodium pump are
related to membrane fluidity and thickness. In general, lipids that promote bilayer
formation of physiological thickness and increased fluidity tend to promote optimal
Na+-K+-ATPase activity (172,186, 221), as do negatively charged lipids such as
phosphatidylserine and phosphatidylglycerol (187). The effects of cholesterol on

4. enzyme activity are often also related to membrane fluidity (140), although specific
effects of cholesterol on the sodium pump have been reported (356). Free fatty acids
present in the membrane or as the products of phospholipase A2 (PLA2)-dependent
regulatory pathway tend to inhibit the Na+-K+-ATPase (254).
The Lp Blood Group Antigen
A striking and mechanistically well-characterized tissue-specific modulator of the
Na+-K+-ATPase is the Lp antigen of LK ruminant red cells, in particular those of
sheep. The Lp antigen is so called because of its association with the L blood group
antigens and its highly specific effects on the sodium pump (reviewed in Ref. 103).
Evidence for the existence of this inhibitor was derived from studies on the effects of
an antiserum specific for the Lp antigen; treatment with anti-Lp stimulates Na+-K+ATPase of LK, but not of high-K+ (HK), erythrocytes (104). In addition,
trypsinization of intact cells reverses the effects of anti-Lp (199), providing evidence
that the inhibitor is a peptide distinct from the sodium pump itself and that the anti-Lp
epitope is removed upon trypsin treatment. Experiments using anti-Lp and trypsin
have led to a model of Lp-mediated inhibition of Na+-K+-ATPase whereby the antigen
inhibits sodium pump activity in two distinct ways. One is secondary to an Lp antigeninduced increase in the susceptibility of pumps to noncompetitive inhibition by K+
(102) and the other to an increase in pump protein turnover during red cell maturation
(352). In the pump/red cell fusion experiments mentioned above, it was observed that
rat kidney pumps fused into LK red blood cells were stimulated by anti-Lp, providing
unequivocal proof that the Lp antigen is a molecular entity distinct from the sodium
pump. However, the exact molecular nature of the protein remains unknown.
Components of the Cytoskeleton
Interactions of the Na+-K+-ATPase with components of the cytoskeleton of cells are
well documented. Specific cytoskeletal proteins thought to interact with the sodium
pump, either directly or indirectly, include spectrin (182), actin (190), adducin (330),
pasin (193), and ankyrin (245). Generally, ankyrin appears to mediate associations
between the sodium pump and other cytoskeletal proteins, although direct
associations of the enzyme with pasin and actin have also been observed. The two
specific domains of the sodium pump that interact with ankyrin have been recently
identified (96, 361). Of these, residues in the first cytoplasmic domain (142–166 of
the rat α1-isoform) are especially intriguing because this region is highly conserved in
all sodium pump isoforms and in H,K- and Ca2+-ATPases, suggesting interactions of
these P-type ion pumps with ankyrin. Ankyrin binding to the second cytoplasmic loop
is likely mediated by a four-residue motif (ALLK) that has homology to a sequence of
the anion exchanger, another ankyrin-binding transporter (174).
The main consequence of interactions between the Na+-K+-ATPase and the
cytoskeleton is believed to be the correct processing and targeting of sodium pumps to
the appropriate membrane compartment. For example, disruptions in the cellular
distribution of Na+-K+-ATPase, induced either by ATP depletion or hypoxia, are
linked to alterations in cytoskeletal proteins (233, 262), and a spectrin-ankyrin
complex is required for transport of pumps from the endoplasmic reticulum to the
Golgi apparatus (97). Recently, a role for cytoskeletal proteins in regulating sodium
pump activity has been suggested. For example, monomeric, but not polymerized,

5. actin has been shown to activate the sodium pump by a mechanism mediated by
cAMP-dependent protein kinase (PKA) (60, 61). In addition, mutant forms of adducin
have been shown to stimulate Na+-K+-ATPase activity in transfected NRK-52E cells
(330).
The identification of genetic polymorphisms in adducin in Milan hypertensive strain
rats and in humans has led Manunta et al. (219) to suggest that adducin variants may
affect kidney function by modulating the overall cation transport in renal epithelia,
both by affecting assembly of the cytoskeleton and by modulating sodium pump
activity. In a recent report, they showed that both rat and human adducins stimulate
Na+-K+-ATPase activity by increasing the apparent affinity for ATP (114).
Interestingly, the mechanism appears to involve acceleration of the rate of the
conformational change E2(K) → E1(Na) or E2(K).ATP → E1Na.ATP. Stimulation is
specific in that a stimulatory effect noted also with ankyrin, which also binds Na+-K+ATPase, is not additive. In general, these findings suggest a specific interaction
between adducin and the Na+-K+-ATPase of the kidney. It is intriguing that the effect
is similar to that effected by the γ-subunit of the pump (see below). Whether
interaction of adducin with the pump involves the γ-subunit is relevant to the
modulatory effect of adducin remains to be determined.
The γ-Subunit
The γ-subunit is a small transmembrane protein that specifically associates with the
Na+-K+-ATPase in a tissue-specific manner. Though its existence had been previously
suggested (282), it was Forbush and co-workers (124) who first demonstrated that this
small hydrophobic peptide is specific to the sodium pump by showing that it is
specifically labeled, along with the α-subunit, by a photoactive derivative of ouabain.
Although the peptide was at first thought to represent a third component of the Na+K+-ATPase, recent evidence suggests that it is not an integral part of the enzyme
complex.
Following the report of Forbush et al. (124), who studied the pig enzyme, experiments
using various ouabain derivatives resulted in the identification of a small sodium
pump-associated proteolipid in various tissues (151, 214, 284,286). This peptide,
initially referred to as “γ component” or “γ-subunit” (281), appeared to be present in
approximately equimolar amounts compared with the α- and β-subunits (85, 155). The
initial molecular cloning experiments indicated that the γ-subunit consisted of 58
amino acids and had a molecular mass of ∼6,500 Da (228). Since then, cDNAs for the
human (185) and Xenopuslaevis (25) γ-subunits have also been cloned and sequenced.
Sequence comparisons show strong homology (75%) among different species, which
is further increased to 93% when only mammalian sequences are compared. Structural
analysis has revealed that the γ-subunit contains a single transmembrane domain, with
an NH2 terminus-out, COOH terminus-in topology (25, 325). The NH2terminus, at
least that of the rat sequence, has since been shown to be somewhat longer and
different than originally reported. (For details, see Ref. 326 and GenBank accession
no.AF129400.1).
An intriguing feature of the γ-subunit structure is that it is detected as two species
with similar amino acid composition irrespective of the protein separation methods
used (for examples, see Refs. 85, 228, 304). Early evidence suggested that the two

6. bands detected on Western blots, henceforth referred to as γaandγb, are the products of
a single mRNA species (228). Béguin and co-workers (25) later showed that in
Xenopus, the two bands of γ are due to alternate usage of two distinct start codons in
the γ-subunit message; only one appears relevant in vivo in this species. However,
recent mass spectrometry analysis of the rat protein indicated that γa and γb are
variants, most likely splice variants (194). γa has a mass of 7,184 Da, whereas the
faster migrating γb species has a mass of 7,354 Da and contains only a different NH2
terminus (6- replacing 7-residues). In fact, their amino acid sequences indicate that
they correspond exactly to two splice variants contained in the expressed sequence tag
database as noted by Sweadner et al. (315). Recent expression studies show clearly
that the γa and γb protein products of transcription/translation have the same mobilities
as the upper and lower bands, respectively, of the kidney medulla (195). Depending
on the cell line used, additional bands, presumably the products of posttranslational
modification, are seen, namely, γ′a with higher apparent mobility than γa in HEK and
γ′b with lower mobility than γb in HeLa, whereas only γaandγb are detected in HeLa
and HEK, respectively.
The expression of γ-subunit mRNA has been investigated by Northern blot analysis in
the rat, human, and X. laevis, and it was shown that the peptide is expressed in a
tissue-specific manner in these species. Thus, in humans, γ-subunit mRNA was
detected in kidney, pancreas, and fetal liver (185), and inXenopus, it was detected
mainly in kidney and stomach, with trace amounts in heart, skin, and oocytes (25). In
rats, the situation is more complex, because two distinct mRNA species were detected
by using the rat γ-subunit cDNA as a probe (228). The larger of the two, at 1.5 kb,
corresponds in size to the Xenopus mRNA and was detected mainly in kidney and
spleen, with lower amounts in lung, heart, and brain. The smaller transcript migrated
at 0.8 kb, a size similar to that of human γ-subunit message, and was detected at high
levels in the kidney and at very low levels in the spleen, lung, and heart. Also in the
rat, Therien and co-workers (325, 326) have recently shown that at the protein level,
the γ-subunit is expressed only in kidney tubules, with very low levels found in the
spleen.
Most available data indicate that the γ-subunit is not expressed at the plasma
membrane without the Na+-K+-ATPase, except perhaps in very early development, as
described below. For example, γ-subunit is expressed at the surface of
Xenopusoocytes only on coinjection of cRNA for the α- and β-subunits (25);
immunocytochemical analysis has shown that the expression patterns of α- and γsubunits are identical in renal proximal tubules and collecting ducts (228), although γsubunit appears to be absent in other parts of the kidney (13, 325). In addition,
coimmunoprecipitation of the γ-subunit with both the α- and β-subunits has been
demonstrated (228). On the other hand, in their study on the role of the γ-subunit in
mouse blastocyst development, Jones and co-workers (173) have shown that the γsubunit is expressed at high levels at the apical membrane, whereas the α- and βsubunits are present only at the basolateral membrane.
The first attempts at defining a functional role for the γ-subunit indicated that this
peptide is not essential for normal enzyme function. For example, Hardwicke and
Freytag (155) were able to show that separation of the γ-peptide from the αβ complex
by nonionic detergent solubilization of shark rectal gland and avian salt gland
membranes had no effect on Na+-K+-ATPase activity. More recently, it has been

7. shown that the presence of the γ-subunit is not necessary for functional expression of
the sodium pump in insect cells (95), Xenopus oocytes (25), and yeast (296). In the
latter system, the γ-subunit was shown to have no effect on either ouabain-sensitive
Na+-K+-ATPase activity or86Rb+ influx. The failure to detect γ-subunit mRNA (25,
185, 228) or protein (325) in many tissues also supports the notion that the γ-subunit
is not an essential component of the Na+-K+-ATPase.
Recent experiments have shown that the γ-subunit has a potentially important
functional role in some systems. Treatment of mouse blastocysts with γ-subunit
antisense oligodeoxynucleotide reduced the amount of expressed γ-subunit and
caused a reduction in ouabain-sensitive 86Rb+ transport as well as delayed blastocoele
formation (173). In experiments on cRNA-injected Xenopus oocytes, the γ-subunit
has been shown to influence the apparent affinity of the Na+-K+-ATPase for K+ in a
complex Na+- and voltage-dependent fashion (25), although the interpretation of these
results remains unclear. A role of the γ-subunit in interactions of the Na+-K+-ATPase
with K+ had previously been suggested by Or et al. (259), who showed that the γsubunit is a component of the protein complex found in so-called “19-kDa
membranes.” Such membranes are formed by tryptic digestion following occlusion of
K+ (or Rb+) by the enzyme to form E2(K) (181). More recently, Arystarkhova et al.
(13) reported that the γ-subunit decreases both Na+ and K+ affinities of the sodium
pump when transfected into NRK-52E cells transfected with γacDNA (13). However,
the decrease in Na+ affinity is difficult to reconcile with the following:1) the increase
in K′Na(∼10-fold) is much larger than that (2-fold) observed for kidney compared with
γ-subunit-free tissues (324,327) if one takes into account the level of expression, and
2) a change in K′Na could only be detected with cells expressing both γ′aandγa, and not
γa alone, despite the finding (195) that γ′a appears to be a cell-specific modification of
γa. In another recent report, the human γ-subunit has been shown to induce ouabainindependent ion currents in injected Xenopus oocytes and 86Rb+ and 22Na+influx in
baculovirus-infected Sf-9 cells (231). As described below, it is unclear whether this
channel-like function is physiologically relevant, an artifact of high-level expression,
or peculiar to human γ-subunit, for which the primary sequence at the extracellular
amino terminus is notably different from that for several other species (231).
In addition to the aforementioned studies on baculovirus-infected Sf-9 cells, cRNAinjected Xenopus oocytes, and transfected NRK-52E cells, the possible functional role
of the γ-subunit has recently been investigated in human HeLa and HEK cells. The
initial approach was to test what effects, if any, an anti-γ antiserum had on the
function of the sodium pump of rat kidney. A specific effect was evidenced in the
finding that anti-γ inhibits Na+-K+-ATPase turnover in kidney, but not in tissues that
do not express γ-subunit (325), and that a peptide corresponding to the epitope of the
antiserum can abrogate the effect (326). Further analysis of the functional effects of
anti-γ showed that it stabilizes the E2 form(s) of the enzyme. Thus the pH-dependence
of the anti-γ-mediated inhibition of activity, together with the observation that Rb+
protects against tryptic digestion of the γ-peptide (325), are consistent with a role of
anti-γ in shifting the equilibrium of the K+-deocclusion reaction [E2(K) ↔ E1] toward
E2(K). On the basis of the well-documented effects of anti-Lp antigen on the kinetics
of the LK sheep red blood cell Na+-K+-ATPase (see above), it was hypothesized that
anti-γ mediates its effects by disrupting interactions between the Na+-K+-ATPase
complex and the γ-subunit such that the role of the γ-subunit is to shift the
aforementioned equilibrium toward E1. By transfecting the γ-subunit into HEK cells,

8. it was recently shown that this is indeed the case (326). These experiments with
transfected cells showed that the γ-subunit stabilizes the E1 conformation of the Na+K+-ATPase by increasing the affinity of the enzyme for ATP at its low-affinity site
and that anti-γ reverses this increase in affinity in transfected cells (326). These
findings, taken together with the observation that inhibition of Na+-K+-ATPase
activity by anti-γ in the renal enzyme was increased at subsaturating concentrations of
ATP, provide strong support for the conclusion that anti-γ reverses γ-subunitmediated effects. It should be noted that a γ-subunit-mediated increase in the affinity
of the enzyme for ATP may lead to a secondary decrease in its apparent affinity for
K+ (328), which would agree with the results of Arystarkhova et al. (13) regarding γsubunit-mediated decrease in K+ affinity. However, it is likely to be the change in
ATP affinity that is physiologically important, as described below.
What is the physiological importance of a regulator of the affinity of the sodium pump
for ATP? In most cells, ATP levels are sufficient to saturate the Na+-K+-ATPase, and
therefore a modest shift in ATP affinity should not have dramatic effects. However,
there are cases where ATP levels in intact cells are dramatically lowered, such as
during anoxic shock. The relationship between anoxia, or hypoxia, and cellular ATP
concentration has been studied in many tissues (15, 171, 191,210, 230, 260,310). As
might be expected, dramatic decreases in ATP levels (30–90%) have been reported
following brief periods of oxygen and/or glucose deprivation. In many cases, ATP
concentration under anoxic conditions falls to a value that will affect Na+-K+-ATPase
activity, assuming aK′ATP of 400–800 mM (310). For example, Koop and Cobbold
(191) estimated that chemical hypoxia lowers the concentration of ATP in intact
hepatocytes to 50–100 μM. In addition, Milusheva et al. (230) reported that
incubation of rat striatal brain slices under glucose-free, hypoxic conditions for a
relatively short period of time (30 min) can decrease cytoplasmic ATP levels to 10%
of control, which, even assuming a relatively high starting concentration of 5 mM,
translates to <500 μM. Finally, a direct correlation between hypoxia and sodium
pump activity was provided by Aw and Jones (15), who observed a near total
inhibition of sodium pump-mediated Rb+ uptake in hepatocytes under conditions
where ATP levels dropped a mere 40%. It might be argued that in the aforementioned
studies, anoxia was induced artificially, and that such conditions may not be relevant
to situations in vivo. However, recent studies have shown that even in normal,
disease-free organisms, at least one tissue, the kidney medulla, must function under
near-anoxic conditions (reviewed in Refs. 56, 81). As is the case in most segments of
the nephron, water and solute reabsorption and secretion in the medulla are under the
control of the sodium pump. As such, continued pumping is crucial for proper kidney
function. Therefore, the existence of a reversible regulator of Na+-K+-ATPase ATP
affinity would allow for fine tuning of sodium pump activity under ATP-depleted
conditions. This regulator should alter the affinity of the pump for the nucleotide only
moderately, because an excessive increase would effect even greater decreases in
ATP concentration (310), leading to compromised cell viability.
The γ-Subunit as a Member of a Family of Proteins
In recent years, several small single-transmembrane-domain peptides with high
sequence homology to the γ-subunit have been identified. As such, studies on these
peptides may reveal interesting information on the structure and function of the γsubunit. To date, in addition to the γ-subunit itself, three members of this family have

9. been cloned: phospholemman (PLM) (263), channel-inducing factor (CHIF) (14), and
mammary tumor-associated 8-kDa protein (Mat-8) (237). Cloned sequences of these
peptides include PLM of the mouse (48), dog (263), rat, and human (72), CHIF of the
rat (14), and Mat-8 of the human (238) and mouse (237). Two additional sequences
with homology to the γ-subunit family of proteins are known, namely, a
“phospholemman-like protein” in humans (HPLP; Ref. 17), and a “regulated ion
channel homologue” (RIC; Ref. 128) in the mouse. The amino acid sequences of the
rat γ-subunit, CHIF, PLM, and mouse Mat-8 are compared in Fig. 1. For the rat γsubunit, the revised sequence of γa is shown (231, 326), whereas for PLM, CHIF, and
Mat-8, the sequences for the mature proteins, after cleavage of their putative signal
peptide (see below), are shown. As illustrated in Fig.1, the latter three proteins have
38–43% homology with the γ-subunit, and this value increases to 74–80% in the
transmembrane domain and immediate flanking sequences (P18to C52 of the rat γsubunit). There are several highly conserved motifs present in most of the known
sequences of this family of proteins. With the use of numbering for the rat γ-subunit,
these motifs include 1) P18FXYD in the extracellular domain, 2) G29G in the
transmembrane domain, and3) S47X(R/K)C(R/K)C flanking the transmembrane
domain on the cytoplasmic side. It should be noted, however, that in the γ-subunit, the
third motif described above contains a Phe residue instead of the first Cys.
Interestingly, Gly-30, Gly-41, and Ser-47 are 100% conserved among all known
sequences. Of these, Ser-47 is especially intriguing because the nearby presence of
positive charges (either K or R) make it a possible target for phosphorylation by
protein kinase C (PKC).
Researchers have established the structure of a crucial enzyme -- the so-called sodium-potassium pump
-- which forms part of every cell in the human body. The result may pave the way for a better
understanding of neurological diseases.
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10. The figure shows the tunnel-like entry point to the binding sites of the sodiumpotassium pump in the sodium-bound state. The three small sodium ions are bound
inside the pump (violet spheres to the left), whereas there is not sufficient room for
the larger potassium ions (green spheres to the right). The blue web shows the inner
surface of the protein blocking the potassium ions. The letter code indicates the amino
acids shown in the pump, which are essential to the binding process.
Credit: BenteVilsen and Flemming Cornelius
[Click to enlarge image]
It's not visible to the naked eye and you can't feel it, but up to 40 per cent of your body's
energy goes into supplying the microscopic sodium-potassium pump with the energy it
needs. The pump is constantly doing its job in every cell of all animals and humans. It
works much like a small battery which, among other things, maintains the sodium balance
which is crucial to keep muscles and nerves working.
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The sodium-potassium pump transports sodium out and potassium into the cell in a fixed cycle. During
this process the structure of the pump changes. It is well-established that the pump has a sodium and a
potassium form. But the structural differences between the two forms have remained a mystery, and
researchers have been unable to explain how the pump distinguishes sodium from potassium.
Structure solves the mystery
Thanks to the international collaboration between Professor Chikashi Toyoshima's group at the
University of Tokyo and researchers from Aarhus University, the structure of the sodium-bound form
of the protein has now been described. For the first time ever, the sodium ions can be studied at a
resolution so high - 0.28 nanometres - that researchers can actually see the sodium ions and observe
where they bind in the structure of the pump. In 2000, Professor Chikashi Toyoshima's group described
the structure of a calcium-pump for the first time, and in 2007 and 2009 research groups from Aarhus
University and Toyoshima's group described the potassium-bound form of the sodium-potassium
pump.
"The new protein structure shows how the smaller sodium ions are bound and subsequently transported
out of the cell, whereas the access of the slightly larger potassium ions is blocked. We now understand
how the pump distinguishes between sodium and potassium at the molecular level. This is a great leap

11. forward for research into ion pumps and may help us understand and treat serious neurological
conditions associated with mutations of the sodium-potassium pump, including a form of Parkinsonism
and alternating hemiplegia of childhood in which sodium binding is defective," explains BenteVilsen, a
professor at Aarhus University who spearheaded the project's activities in Aarhus with Associate
Professor Flemming Cornelius.
Impressed Nobel Prize winner
The vital pump was discovered in 1957 by Professor Jens Christian Skou of Aarhus University, who
received the Nobel Prize for his discovery in 1997. The new result is the culmination of five or six
decades of research aimed at the mechanism behind this vital motor of the cells.
"Years ago, when the first electron microscopic images were taken in which the enzyme was but a
millimetre-sized dot at 250,000 magnifications, I thought, how on earth will we ever be able to
establish the structure of the enzyme. The pump transports potassium into and sodium out of the cells,
so it must be capable of distinguishing between the two ions. But until now, it has been a mystery how
this was possible," says retired Professor Jens Christian Skou, who - even at 94 years of age - keeps up
to date with new developments in the field of research which he initiated more than 50 years ago.
"Now, the researchers have described the structure that allows the enzyme to identify sodium and this
may pave the way for a more detailed understanding of how the pump works. It is an impressive
achievement and something I haven't even dared dream of," concludes Jens Christian Skou.
Story Source:
The above story is based on materials provided by Aarhus University. Note:
Materials may be edited for content and length.

13. From Wikipedia, the free encyclopedia
Flow of ions.
Alpha and beta units.

14. Sodium-potassium pump, E2-Pi state. Calculated hydrocarbon boundaries of the lipid
bilayer are shown as blue (intracellular) and red (extracellular) planes
Na+
/K+
-ATPase (Sodium-potassium adenosine triphosphatase, also known as Na+
/K+
pump, sodium-potassium pump, or sodium pump) is an antiporterenzyme (EC3.6.3.9)
(an electrogenictransmembraneATPase) located in the plasma membrane of all animal
cells. The Na+
/K+
-ATPase enzyme pumps sodium out of cells, while pumping potassium into cells.
Contents
1 Sodium-potassium pumps
2 Function
o 2.1 Resting potential
o 2.2 Transport
o 2.3 Controlling cell volume
o 2.4 Functioning as signal transducer
o 2.5 Controlling neuron activity states
3 Mechanism
4 Regulation
o 4.1 Endogenous
o 4.2 Exogenous
5 Discovery
6 Genes
7 See also
8 References
9 Additional images
10 External links
Sodium-potassium pumps

15. Active transport is responsible for cells' containing relatively high concentrations of
potassium ions but low concentrations of sodium ions. The mechanism responsible for
this is the sodium-potassium pump, which moves these two ions in opposite directions
across the plasma membrane. This was investigated by following the passage of
radioactively labeled ions across the plasma membrane of certain cells. It was found
that the concentrations of sodium and potassium ions on the two sides of the
membrane are interdependent, suggesting that the same carrier transports both ions. It
is now known that the carrier is an ATP-ase and that it pumps three sodium ions out
of the cell for every two potassium ions pumped in.
The sodium-potassium pump was discovered in the 1950s by a Danish scientist, Jens
Christian Skou, who was awarded a Nobel Prize in 1997. It marked an important step
forward in our understanding of how ions get into and out of cells, and it has a
particular significance for excitable cells such as nervous cells, which depend on this
pump for responding to stimuli and transmitting impulses.
Function
The Na+
/K+
-ATPase helps maintain resting potential, avail transport, and regulate cellular
volume.[1] It also functions as signal transducer/integrator to regulate MAPK pathway,
ROS, as well as intracellular calcium. In most animal cells, the Na+
/K+
-ATPase is responsible for about 1/5 of the cell's energy expenditure.[citation needed] For
neurons, the Na+
/K+
-ATPase can be responsible for up to 2/3 of the cell's energy expenditure.[2]
Resting potential
See also: Resting potential
In order to maintain the cell membrane potential, cells keep a low concentration of
sodium ions and high levels of potassium ions within the cell (intracellular). The
sodium-potassium pump moves 3 sodium ions out and moves 2 potassium ions in,
thus in total removing one positive charge carrier from the intracellular space. Please
see Mechanism for details.
The action of the sodium-potassium pump is not the only mechanism responsible for
the generation of the resting membrane potential. Also, the selective permeability of
the cell's plasma membrane for the different ions plays an important role. All
mechanisms involved are explained in the main article on generation of the resting
membrane potential.
Transport

16. Export of sodium from the cell provides the driving force for several secondary active
transporters membrane transport proteins, which import glucose, amino acids, and
other nutrients into the cell by use of the sodium gradient.
Another important task of the Na+
-K+
pump is to provide a Na+
gradient that is used by certain carrier processes. In the gut, for example, sodium is
transported out of the reabsorbing cell on the blood (interstitial fluid) side via the Na+
-K+
pump, whereas, on the reabsorbing (luminal) side, the Na+
-Glucose symporter uses the created Na+
gradient as a source of energy to import both Na+
and glucose, which is far more efficient than simple diffusion. Similar processes are
located in the renal tubular system.
Controlling cell volume
Failure of the Na+
-K+
pumps can result in swelling of the cell. A cell's osmolarity is the sum of the
concentrations of the various ion species and many proteins and other organic
compounds inside the cell. When this is higher than the osmolarity outside of the cell,
water flows into the cell through osmosis. This can cause the cell to swell up and lyse.
The Na+
-K+
pump helps to maintain the right concentrations of ions. Furthermore, when the cell
begins to swell, this automatically activates the Na+
-K+
pump.[citation needed]
Functioning as signal transducer
Within the last decade [when?], many independent labs have demonstrated that, in
addition to the classical ion transporting, this membrane protein can also relay
extracellular ouabain-binding signalling into the cell through regulation of protein
tyrosine phosphorylation. The downstream signals through ouabain-triggered protein
phosphorylation events include activation of the mitogen-activated protein kinase
(MAPK) signal cascades, mitochondrial reactive oxygen species (ROS) production, as
well as activation of phospholipase C (PLC) and inositol triphosphate (IP3) receptor
(IP3R) in different intracellular compartments.[3]
Protein-protein interactions play a very important role in Na+
-K+
pump-mediated signal transduction. For example, Na+
-K+
pump interacts directly with Src, a non-receptor tyrosine kinase, to form a signaling
receptor complex.[4]Src kinase is inhibited by Na+
-K+
pump, while, upon ouabain binding, the Src kinase domain will be released and then

17. activated. Based on this scenario, NaKtide, a peptide Src inhibitor derived from Na+
-K+
pump, was developed as a functional ouabain-Na+
-K+
pump-mediated signal transduction.[5] Na+
-K+
pump also interacts with ankyrin, IP3R, PI3K, PLC-gamma and cofilin.[6]
Controlling neuron activity states
The Na+
-K+
pump has been shown to control and set the intrinsic activity mode of
cerebellarPurkinje neurons.[7] This suggests that the pump might not simply be a
homeostatic, "housekeeping" molecule for ionic gradients; but could be a computation
element in the cerebellum and the brain. Indeed, a mutation in the Na+
-K+
pump causes rapid onset dystonia parkinsonism, which has symptoms to indicate that
it is a pathology of cerebellar computation.[8] Furthermore, an ouabain block of Na+
-K+
pumps in the cerebellum of a live mouse results in it displaying ataxia and dystonia.[9]
The distribution of the Na+
-K+
pump on myelinated axons, in human brain, was demonstrated to be along the
internodalaxolemma, and not within the nodal axolemma as previously thought.[10]
Mechanism
The pump, while binding ATP, binds 3 intracellular Na+
ions.[1]
ATP is hydrolyzed, leading to phosphorylation of the pump at a highly
conserved aspartate residue and subsequent release of ADP.
A conformational change in the pump exposes the Na+
ions to the outside. The phosphorylated form of the pump has a low affinity
for Na+
ions, so they are released.
The pump binds 2 extracellular K+
ions. This causes the dephosphorylation of the pump, reverting it to its
previous conformational state, transporting the K+
ions into the cell.

18. The unphosphorylated form of the pump has a higher affinity for Na+
ions than K+
ions, so the two bound K+
ions are released. ATP binds, and the process starts again.
Regulation
Endogenous
The Na+
/K+
-ATPase is upregulated by cAMP.[11] Thus, substances causing an increase in
cAMPupregulate the Na+
/K+
-ATPase. These include the ligands of the Gs-coupled GPCRs. In contrast, substances
causing a decrease in cAMPdownregulate the Na+
/K+
-ATPase. These include the ligands of the Gi-coupled GPCRs.
Note: Early studies indicated the opposite effect, but these were later found to be
inaccurate due to additional complicating factors.[citation needed]
Exogenous
The Na+
-K+
-ATPase can be pharmacologically modified by administrating drugs exogenously.
For instance, Na+
-K+
-ATPase found in the membrane of heart cells is an important target of cardiac
glycosides (for example digoxin and ouabain), inotropic drugs used to improve heart
performance by increasing its force of contraction.
Contraction of any muscle is dependent on a 100- to 10,000-times-higher-than-resting
intracellular Ca2+
concentration, which, as soon as it is put back again on its normal level by a carrier
enzyme in the plasma membrane, and a calcium pump in sarcoplasmic reticulum,
muscle relaxes.
Since this carrier enzyme (Na+
-Ca2+
translocator) uses the Na gradient generated by the Na+
-K+
pump to remove Ca2+
from the intracellular space, slowing down the Na+
-K+
pump results in a permanently elevated Ca2+

19. level in the muscle, which may be the mechanism of the long-term inotropic effect of
cardiac glycosides such as digoxin.
Discovery
Na+
/K+
-ATPase was discovered by Jens Christian Skou in 1957 while working as assistant
professor at the Department of Physiology, University of Aarhus, Denmark. He
published his work that year.[12]
In 1997, he received one-half of the Nobel Prize in Chemistry "for the first discovery
of an ion-transporting enzyme, Na+
, K+
-ATPase."[13]
Vasopressin or anti diuretic hormone (ADH) is released from the posterior pituitary
gland in response to low blood volume. ADH synthesis occurs at the supraoptic
nucleus of the hypothalamos and is storage at the posterior pituitary. This hormone
has three main functions: increase water reabsorption, vasoconstriction, and promotes
release of coagulation factor VIII. The first function is achieved via activation of the
V2 receptors at the level of the renal tubules. Via a G-protein couple pathway ADH
increases the expression and function of the aquaporins, special proteins at the
luminal side of the renal tubules that work in water reabsorption. The second function
of ADH is achieved by activation of V1 receptors in the blood vessels. The activation
of these receptors cause an increase in the intracellular calcium levels and as a result
constriction of the smooth muscle cells of the blood vessels, causing vasoconstriction
or increase in the peripheral vascular resistance. Through these mechanisms ADH
helps in the maintenance of a „normal‟ blood volume and osmolarity and in the
regulation of blood pressure. Diabetes insipidus (DI) is a pathological condition where
there is diminished response to ADH. It can be secondary to a decreased release of the
hormone (central or neurogenic DI) or to an inadequate response at the kidneys
(nephrogenic DI). Patients with DI will have an increased urinary volume, and the
urine will be hypotonic in comparison with the serum osmolarity.
ADH is synthetised in the hypothalamus & is transported to the posterior pituitary.
ADH is a nonapeptide produced in the supraoptic and paraventricular nuclei and other
areas of the hypothalamus. Its major role is in the regulation of water balance by its
effect on the kidneys. ADH is also known as vasopressin because of the vasopressor
response to pharmacological doses. Humans and most animals have argininevasopressin but pigs have the arginine replaced by a lysine.

20. ADH is produced from a much larger precursor protein (prepropressophysin). The
gene for this precursor is located on human chromosome 20 and is very closely
related to the oxytocin gene. These genes probably arose from an ancestral gene as a
result of gene duplication about 350 million years ago. The ADH precursor protein
contains sequences for three separate peptides into which it is split during transport
down the nerve axon to the posterior pituitary. These are ADH, neurophysin& a
glycopeptide. The physiological role of these later two peptides is unclear but
neurophysin may have a role as a carrier or binding protein within the granules.
The secretory granules containing the ADH and neurophysin move down the axons
(axonal transport) to the nerve terminals in the posterior pituitary from where they are
secreted into the systemic circulation by a process of exocytosis (involving calcium).
Intravascular ADH has a half-life of only about 15 minutes being rapidly metabolised
in the liver and kidney to inactive products.
5.6.2 Renal Actions of ADH
ADH acts on receptors in the basolateral membrane of cells in the cortical and
medullary collecting tubules and not on the apical (or luminal) membrane. These
membranes have different properties. The apical membrane of these cells is
impermeable to water in the absence of ADH but the basolateral membrane is always
permeable to water.
ADH initiates its physiological actions by combining with a specific receptor. These
are two major types of vasopressin receptors: V1 & V2. The V1 receptors are located
on blood vessels and are responsible for the vasopressor action.
The V2 receptors are in the basolateral membrane of the collecting tubule cells in the
kidney. Various agonists and antagonists at these receptors have been developed.
Desamino-d-arginine vasopressin (dDAVP) is a synthetic V2-agonist which is used
clinically in treatment of diabetes insipidus.
The action at the V2 receptor activates adenylcyclase and cyclic AMP (second
messenger) is formed. This initiates a series of events which causes specific vesicles
in the cytoplasm to move to and fuse with the apical membrane. The vesicles contain
the water channels (aquaporin 2) which are now inserted in the apical (ie luminal)
membrane rendering it permeable to water. Water moves into the cell through these
channels in response to the osmotic gradient. It passes into the circulation across the
basolateral membrane. The basolateral membrane is always freely permeable to water
but the apical membrane is permeable only when the water channels are inserted.
When intracellular cyclic AMP levels fall, the water channels are removed from the
membrane and reform as vesicles.
The cycle of insertion of water channels into then removal from the luminal
membrane is referred to as vesicular trafficking and is the final mediator of the ADHdependent water permeability of the collecting duct cells.

21. The water channels are membrane proteins called aquaporins. Aquaporin-2 is the
protein which is the vasopressin responsive water channel in the collecting duct. It is
inserted into the apical membrane in reponse to cyclic AMP. The protein forms a
tetrameric complex that spans the membrane and forms a channel which allows rapid
water movement in response to an osmolar gradient.
Aquaporins 3 & 4 are the water channels located in the basolateral membrane. Their
water permeability is not altered by ADH action and their presence means the
basolateral membrane has a continuous water permeability.
Other interesting recent findings in this area are:
Mercurial diuretics bind to a specific site on aquaporin-2 and block water
reabsorption. This is the mechanism of their diuretic action
The autosomal dominant form of nephrogenic diabetes insipidus is due to
mutations in the aquaporin-2 gene
The X-linked form of nephrogenic diabetes is due to mutations in the gene for
the V2 vasopressin receptor. (This receptor gene is on the X chromosome)
Lithium causes marked down-regulation of aquaporin-2 expression and causes
a form of acquired nephrogenic diabetes insipidus
Overall Effects in the Kidney
In the absence of ADH, the apical membranes of the cells in the cortical and
medullary collecting tubules have very low water permeability. Large volumes
of hypotonic urine are produced. Up to 12% of the filtered load of 180l/day is
excreted (urine volume up to 23 liters/day!)
In the presence of ADH, the cells are much more permeable to water. At
maximal ADH levels, less then 1% of the filtered water is excreted (urine
volume 500mls/day)
Feedback loop: Reabsorption of water reduces plasma [Na+] and this is
detected by the osmoreceptors in the hypothalamus. This allows sensitive
feedback control of ADH secretion. (Aquaporin 4 is found in the cells of the
thirst centre in the hypothalamus and is probably involved in the mechanism
which monitors plasma tonicity)
Maintaining Water Volume
Your kidneys have the ability to conserve or waste water. For example, if you drink a large
glass of water, you'll find that you will have the urge to urinate within an hour or so. In
contrast, if you don't drink for a while, such as overnight, you will not produce much urine
and it will usually be very concentrated (i.e. darker). How does your kidney know the
difference? The answer to this question involves two mechanisms
The structure and transport properties of the loop of Henle in the nephron
The anti-diuretic hormone (ADH), also called vasopressin, secreted by the pituitary gland

22. The loop of Henle has a descending limb and an ascending limb. As filtrate moves down the
loop of Henle, water is reabsorbed, but ions (Na,Cl) aren't. The removal of water serves to
concentrate the Na and Cl in the lumen. Now, as the filtrate moves up the other side
(ascending limb), Na and Cl are reabsorbed, but water isn't. What these two transport
properties do is set up a concentration difference in NaCl along the length of the loop, with
the highest concentration at the bottom and lowest concentration at the top. The loop of
Henle can then concentrate NaCl in the medulla. The longer the loop, the bigger the
concentration gradient. This also means that the medulla tissue tends to be saltier than the
cortex tissue
Now, as the filtrate flows through the collecting ducts, which go back down through the
medulla, water can be reabsorbed from the filtrate by osmosis. Water moves from an area
of low Na concentration (high water concentration) in the collecting ducts to an area of high
Na concentration (low water concentration) in the medullary tissue. If you remove water
from the filtrate at this final stage, you can concentrate the urine
ADH, which is secreted by the pituitary gland, controls the ability of water to pass through
the cells in the walls of the collecting ducts. If no ADH is present, then no water can pass
through the walls of the ducts. The more ADH present, the more water can pass through
Specialized nerve cells, called osmoreceptors, in the hypothalamus of the brain sense the Na
concentration of the blood. The nerve endings of these osmoreceptors are located in the
posterior pituitary gland and secrete ADH. If the Na concentration of the blood is high, the
osmoreceptors secrete ADH. If the Na concentration of the blood is low, they don't secrete
ADH. In reality, there is always some very low level of ADH secreted from the
osmoreceptors
Now let's look at how your kidneys maintain water volume
Vasopressin, also known as arginine vasopressin (AVP), antidiuretic hormone
(ADH), or argipressin, is a neurohypophysial hormone found in most mammals. Its
two primary functions are to retain water in the body and to constrict blood vessels.
Vasopressin regulates the body's retention of water by acting to increase water
absorption in the collecting ducts of the kidney nephron.[1][2] Vasopressin is a peptide
hormone that increases water permeability of the kidney's collecting duct and distal
convoluted tubule by inducing translocation of aquaporin-CD water channels in the
kidney nephron collecting duct plasma membrane.[3] It also increases peripheral
vascular resistance, which in turn increases arterial blood pressure. It plays a key role

23. in homeostasis, by the regulation of water, glucose, and salts in the blood. It is derived
from a preprohormone precursor that is synthesized in the hypothalamus and stored in
vesicles at the posterior pituitary. Most of it is stored in the posterior pituitary to be
released into the bloodstream. However, some AVP may also be released directly into
the brain, and accumulating evidence suggests it plays an important role in social
behavior, sexual motivation and bonding, and maternal responses to stress. It has a
very short half-life between 16-24 minutes.[2]
Contents
1Physiology
o 1.1Function
 1.1.1Kidney
 1.1.2Cardiovascular system
 1.1.3Central nervous system
o 1.2Control
o 1.3Secretion
o 1.4Receptors
2Structure and relation to oxytocin
3Role in disease
o 3.1Lack of AVP
o 3.2Excess AVP
4Pharmacology
o 4.1Vasopressin analogues
o 4.2The role of vasopressin analogues in cardiac arrest
 4.2.1Vasopressin vs. epinephrine
 4.2.2Vasopressin and epinephrine vs. epinephrine alone
 4.2.32010 American Heart Association Guidelines
o 4.3Vasopressin receptor inhibition
5See also
6References
7Further reading
8External links
Physiology
Function
One of the most important roles of AVP is to regulate the body's retention of water; it
is released when the body is dehydrated and causes the kidneys to conserve water,
thus concentrating the urine and reducing urine volume. At high concentrations, it
also raises blood pressure by inducing moderate vasoconstriction. In addition, it has a
variety of neurological effects on the brain, having been found, for example, to
influence pair-bonding in voles. The high-density distributions of vasopressin receptor
AVPr1a in prairie vole ventral forebrain regions have been shown to facilitate and
coordinate reward circuits during partner preference formation, critical for pair bond
formation.[4]

24. A very similar substance, lysine vasopressin (LVP) or lypressin, has the same
function in pigs and is often used in human therapy.
Kidney
Vasopressin has two main effects by which it contributes to increased urine
osmolarity (increased concentration) and decreased water excretion:
1. Increasing the water permeability of distal tubule and collecting duct cells in
the kidney, thus allowing water reabsorption and excretion of more
concentrated urine, i.e., antidiuresis. This occurs through insertion of water
channels (Aquaporin-2) into the apical membrane of distal tubule and
collecting duct epithelial cells. Aquaporins allow water to move down their
osmotic gradient and out of the nephron, increasing the amount of water reabsorbed from the filtrate (forming urine) back into the bloodstream.
V2 receptors, which are G protein-coupled receptors on the basolateral plasma
membrane of the epithelial cells, couple to the heterotrimeric G-protein Gs,
which activates adenylyl cyclases III and VI to convert ATP into cAMP, plus
2 inorganic phosphates. The rise in cAMP then triggers the insertion of
aquaporin-2 water channels by exocytosis of intracellular vesicles, recycling
endosomes. Vasopressin also increases the concentration of calcium in the
collecting duct cells, by episodic release from intracellular stores. Vasopressin,
acting through cAMP, also increases transcription of the aquaporin-2 gene,
thus increasing the total number of aquaporin-2 molecules in collecting duct
cells.
Cyclic-AMP activates protein kinase A (PKA) by binding to its regulatory
subunits and allowing them to detach from the catalytic subunits. Detachment
exposes the catalytic site in the enzyme, allowing it to add phosphate groups to
proteins (including the aquaporin-2 protein), which alters their functions.
2. Increasing permeability of the inner medullary portion of the collecting duct to
urea by regulating the cell surface expression of urea transporters,[5] which
facilitates its reabsorption into the medullary interstitium as it travels down the
concentration gradient created by removing water from the connecting tubule,
cortical collecting duct, and outer medullary collecting duct.
Cardiovascular system
Vasopressin increases peripheral vascular resistance (vasoconstriction) and thus
increases arterial blood pressure. This effect appears small in healthy individuals;
however it becomes an important compensatory mechanism for restoring blood
pressure in hypovolemic shock such as that which occurs during hemorrhage.
Central nervous system

25. Avp is expressed in the periventricular region of the hypothalamus in the adult
mouse.[6]Allen Brain Atlases
Vasopressin released within the brain has many actions:
It has been implicated in memory formation, including delayed reflexes,
image, short- and long-term memory, though the mechanism remains
unknown; these findings are controversial. However, the synthetic vasopressin
analoguedesmopressin has come to interest as a likely nootropic.
Vasopressin is released into the brain in a circadian rhythm by neurons of the
supraoptic nucleus.
Vasopressin released from centrally projecting hypothalamic neurons is
involved in aggression, blood pressure regulation, and temperature regulation.
It is likely that vasopressin acts in conjunction with corticotropin-releasing
hormone to modulate the release of corticosteroids from the adrenal gland in
response to stress, particularly during pregnancy and lactation in
mammals.[7][8][9]
Selective AVPr1a blockade in the ventral pallidum has been shown to prevent
partner preference in prairie voles, suggesting that these receptors in this
ventral forebrain region are crucial for pair bonding.[4]
Recent evidence suggests that vasopressin may have analgesic effects. The
analgesia effects of vasopressin were found to be dependent on both stress and
gender.[10]
Evidence for this comes from experimental studies in several species, which indicate
that the precise distribution of vasopressin and vasopressin receptors in the brain is
associated with species-typical patterns of social behavior. In particular, there are
consistent differences between monogamous species and promiscuous species in the
distribution of AVP receptors, and sometimes in the distribution of vasopressincontaining axons, even when closely related species are compared.[11] Moreover,
studies involving either injecting AVP agonists into the brain or blocking the actions
of AVP support the hypothesis that vasopressin is involved in aggression toward other
males. There is also evidence that differences in the AVP receptor gene between
individual members of a species might be predictive of differences in social behavior.
One study has suggested that genetic variation in male humans affects pair-bonding
behavior. The brain of males uses vasopressin as a reward for forming lasting bonds
with a mate, and men with one or two of the genetic alleles are more likely to

26. experience marital discord. The partners of the men with two of the alleles affecting
vasopressin reception state disappointing levels of satisfaction, affection, and
cohesion.[12] Vasopressin receptors distributed along the reward circuit pathway, to be
specific in the ventral pallidum, are activated when AVP is released during social
interactions such as mating, in monogamous prairie voles. The activation of the
reward circuitry reinforces this behavior, leading to conditioned partner preference,
and thereby initiates the formation of a pair bond.[13]
Control
Vasopressin is secreted from the posterior pituitary gland in response to reductions in
plasma volume, in response to increases in the plasma osmolality, and in response to
cholecystokinin (CCK) secreted by the small intestine:
Secretion in response to reduced plasma volume is activated by pressure
receptors in the veins, atria, and carotids.
Secretion in response to increases in plasma osmotic pressure is mediated by
osmoreceptors in the hypothalamus.
Secretion in response to increases in plasma CCK is mediated by an unknown
pathway.
The neurons that make AVP, in the hypothalamic supraoptic nuclei (SON) and
paraventricular nuclei (PVN), are themselves osmoreceptors, but they also receive
synaptic input from other osmoreceptors located in regions adjacent to the anterior
wall of the third ventricle. These regions include the organumvasculosum of the
lamina terminalis and the subfornical organ.
Many factors influence the secretion of vasopressin:
Ethanol (alcohol) reduces the calcium-dependent secretion of AVP by
blocking voltage-gated calcium channels in neurohypophyseal nerve
terminals.[14]
Angiotensin II stimulates AVP secretion, in keeping with its general pressor
and pro-volumic effects on the body.[15]
Atrial natriuretic peptide inhibits AVP secretion, in part by inhibiting
Angiotensin II-induced stimulation of AVP secretion.[15]
Secretion
The main stimulus for secretion of vasopressin is increased osmolality of plasma.
Reduced volume of extracellular fluid also has this effect, but is a less sensitive
mechanism.
The AVP that is measured in peripheral blood is almost all derived from secretion
from the posterior pituitary gland (except in cases of AVP-secreting tumours).
Vasopressin is produced by magnocellularneurosecretory neurons in the
Paraventricular nucleus of hypothalamus (PVN) and Supraoptic nucleus (SON). It
then travels down the axon through the infundibulum within neurosecretory granules
that are found within Herring bodies, localized swellings of the axons and nerve
terminals. These carry the peptide directly to the posterior pituitary gland, where it is

27. stored until released into the blood. However there are two other sources of AVP with
important local effects:
AVP is also synthesized by parvocellularneurosecretory neurons at the PVN,
transported and released at the median eminence, which then travels through
the hypophyseal portal system to the anterior pituitary where it stimulates
corticotropic cells synergistically with CRH to produce ACTH (by itself it is a
weak secretagogue).[16]
Vasopressin is also released into the brain by several different populations of
smaller neurons.
Receptors
Below is a table summarizing some of the actions of AVP at its four receptors,
differently expressed in different tissues and exerting different actions:
Type
Second messenger system
Locations
Liver, kidney,
peripheral
AVPR1A Phosphatidylinositol/calcium
vasculature,
brain
AVPR1B
Pituitary gland,
or
Phosphatidylinositol/calcium
brain
AVPR3
AVPR2
Adenylatecyclase/cAMP
Basolateral
membrane of
the cells lining
the collecting
ducts of the
kidneys
(especially the
cortical and
outer medullary
collecting
ducts)
Vascular
endothelium
VACM-1 Phosphatidylinositol/calcium and renal
collecting
tubules
Structure and relation to oxytocin
Actions
Vasoconstriction,
gluconeogenesis, platelet
aggregation, and release of
factor VIII and von
Willebrand factor; social
recognition,[17] circadian
tau[18]
Adrenocorticotropic
hormone secretion in
response to stress;[19] social
interpretation of olfactory
cues[20]
Insertion of aquaporin-2
(AQP2) channels (water
channels). This allows water
to be reabsorbed down an
osmotic gradient, and so the
urine is more concentrated.
Release of von Willebrand
factor and surface
expression of P-selectin
through exocytosis of
Weibel-Palade bodies from
endothelial cells[21][22]
Increases cytosolic calcium
and acts as an inverse
agonist of cAMP
accumulation[23]

28. Chemical structure of the argipressin (indicating that this compound is of the
vasopressin family with an arginine at the 8th amino acid position.
Chemical structure of oxytocin
The vasopressins are peptides consisting of nine amino acids (nonapeptides). (NB: the
value in the table above of 164 amino acids is that obtained before the hormone is
activated by cleavage). The amino acid sequence of arginine vasopressin is Cys-TyrPhe-Gln-Asn-Cys-Pro-Arg-Gly, with the cysteine residues forming a disulfide bond.
Lysine vasopressin has a lysine in place of the arginine.
The structure of oxytocin is very similar to that of the vasopressins: It is also a
nonapeptide with a disulfide bridge and its amino acid sequence differs at only two
positions (see table below). The two genes are located on the same chromosome
separated by a relatively small distance of less than 15,000 bases in most species. The
magnocellular neurons that make vasopressin are adjacent to magnocellular neurons
that make oxytocin, and are similar in many respects. The similarity of the two
peptides can cause some cross-reactions: oxytocin has a slight antidiuretic function,
and high levels of AVP can cause uterine contractions.[24][25]
Below is a table showing the superfamily of vasopressin and oxytocin neuropeptides:
Vertebrate Vasopressin Family
Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly- Argipressin Most
NH2
(AVP, ADH) mammals
Pigs,
hippos,
Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Lys-Gly- Lypressin
warthogs,
NH2
(LVP)
some
marsupials
Cys-Phe-Phe-Gln-Asn-Cys-Pro-Arg-GlySome
Phenypressin
NH2
marsupials
Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly- Vasotocin† Non-

29. NH2
mammals
Vertebrate Oxytocin Family
Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly- Oxytocin
NH2
(OXT)
Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Pro-GlyNH2
ProlOxytocin
Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Ile-GlyNH2
Mesotocin
Cys-Tyr-Ile-Gln-Ser-Cys-Pro-Ile-GlySeritocin
NH2
Cys-Tyr-Ile-Ser-Asn-Cys-Pro-Ile-GlyIsotocin
NH2
Cys-Tyr-Ile-Ser-Asn-Cys-Pro-Gln-GlyGlumitocin
NH2
Cys-Tyr-Ile-Asn/Gln-Asn-Cys-ProVarious
Leu/Val-Gly-NH2
tocins
Invertebrate VP/OT Superfamily
Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-Gly- Diuretic
NH2
Hormone
Cys-Phe-Val-Arg-Asn-Cys-Pro-Thr-GlyAnnetocin
NH2
Most
mammals,
ratfish
Some New
World
monkeys,
northern
tree shrews
Most
marsupials,
all birds,
reptiles,
amphibians,
lungfishes,
coelacanths
Frogs
Bony fishes
Skates
Sharks
Locust
Earthworm
Geography
& imperial
Cys-Phe-Ile-Arg-Asn-Cys-Pro-Lys-Gly- Lyscone snail,
NH2
Connopressin pond snail,
sea hare,
leech
Cys-Ile-Ile-Arg-Asn-Cys-Pro-Arg-Gly- ArgStriped
NH2
Connopressin cone snail
Cys-Tyr-Phe-Arg-Asn-Cys-Pro-Ile-GlyCephalotocin Octopus
NH2
Cys-Phe-Trp-Thr-Ser-Cys-Pro-Ile-GlyOctopressin Octopus
NH2
†Vasotocin is the evolutionary progenitor of all the vertebrate
neurohypophysial hormones.[26]
Role in disease

30. Lack of AVP
Decreased AVP release or decreased renal sensitivity to AVP leads to diabetes
insipidus, a condition featuring hypernatremia (increased blood sodium
concentration), polyuria (excess urine production), and polydipsia (thirst).
Excess AVP
High levels of AVP secretion may lead to hyponatremia. In many cases, the AVP
secretion is appropriate (due to severe hypovolemia), and the state is labelled
"hypovolemic hyponatremia". In certain disease states (heart failure, nephrotic
syndrome) the body fluid volume is increased but AVP production is not suppressed
for various reasons; this state is labelled "hypervolemichyponatremia". A proportion
of cases of hyponatremia feature neither hyper- nor hypovolemia. In this group
(labelled "euvolemichyponatremia"), AVP secretion is either driven by a lack of
cortisol or thyroxine (hypoadrenalism and hypothyroidism, respectively) or a very
low level of urinary solute excretion (potomania, low-protein diet), or it is entirely
inappropriate. This last category is classified as the syndrome of inappropriate
antidiuretic hormone (SIADH).[27]
SIADH in turn can be caused by a number of problems. Some forms of cancer can
cause SIADH, particularly small cell lung carcinoma but also a number of other
tumors. A variety of diseases affecting the brain or the lung (infections, bleeding) can
be the driver behind SIADH. A number of drugs has been associated with SIADH,
such as certain antidepressants (serotonin reuptake inhibitors and tricyclic
antidepressants), the anticonvulsant carbamazepine, oxytocin (used to induce and
stimulate labor), and the chemotherapy drug vincristine. It has also been associated
with fluoroquinolones (including ciprofloxacin and moxifloxacin).[2] Finally, it can
occur without a clear explanation.[27]
Hyponatremia can be treated pharmaceutically through the use of vasopressin receptor
antagonists.[27]
Pharmacology
Vasopressin analogues
Vasopressin agonists are used therapeutically in various conditions, and its longacting synthetic analogue desmopressin is used in conditions featuring low
vasopressin secretion, as well as for control of bleeding (in some forms of von
Willebrand disease and in mild haemophilia A) and in extreme cases of bedwetting by
children. Terlipressin and related analogues are used as vasoconstrictors in certain
conditions. Use of vasopressin analogues for esophageal varices commenced in
1970.[28]
Vasopressin infusion has also been used as a second line of management in septic
shock patients not responding to high dose of inotropes (e.g., dopamine or
norepinephrine).

31. The role of vasopressin analogues in cardiac arrest
Injection of vasopressors for the treatment of cardiac arrest was first suggested in the
literature in 1896 when Austrian scientist Dr. R. Gottlieb described the vasopressor
epinephrine as an "infusion of a solution of suprarenal extract [that] would restore
circulation when the blood pressure had been lowered to unrecordable levels by
chloral hydrate."[29] Modern interest in vasopressors as a treatment for cardiac arrest
stem mostly from canine studies performed in the 1960s by anesthesiologists Dr. John
W. Pearson and Dr. Joseph Stafford Redding in which they demonstrated improved
outcomes with the use of adjunct intracardiac epinephrine injection during
resuscitation attempts after induced cardiac arrest.[29] Also contributing to the idea that
vasopressors may be useful treatments in cardiac arrest are studies performed in the
early to mid 1990's that found significantly higher levels of endogenous serum
vasopressin in adults after successful resuscitation from out-of-hospital cardiac arrest
compared to those who did not live.[30][31] Results of animal models have supported
the use of either vasopressin or epinephrine in cardiac arrest resuscitation attempts,
showing improved coronary perfusion pressure[32] and overall improvement in shortterm survival as well as neurological outcomes.[33]
Vasopressin vs. epinephrine
Table 1. Meta-analysis of outcomes for patients treated with vasopressin versus
epinephrine[32]
RR (95% CI)
Failure of ROSC
0.81 (0.58-1.12)
Death before hospital admission
0.72 (0.38-1.39)
Death within 24 hours
0.74 (0.38-1.43)
Death before hospital discharge
0.96 (0.87-1.05)
Number of deaths and neurologically impaired survivors
1.00 (0.94-1.07)
Although both vasopressors, vasopressin and epinephrine differ in that vasopressin
does not have direct effects on cardiac contractility as epinephrine does.[33] Thus,
vasopressin is theorized to be of increased benefit over epinephrine in cardiac arrest
due to its properties of not increasing myocardial and cerebral oxygen demands.[33]
This idea has led to the advent of several studies searching for the presence of a
clinical difference in benefit of these two treatment choices. Initial small studies
demonstrated improved outcomes with vasopressin in comparison to epinephrine.[34]
However, subsequent studies have not all been in agreement. Several randomized
controlled trials have been unable to reproduce positive results with vasopressin
treatment in both return of spontaneous circulation (ROSC) and survival to hospital
discharge,[34][35][36][37] including a systematic review and meta-analysis completed in
2005 that found no evidence of a significant difference with vasopressin in five
studied outcomes (see Table 1).[32]
Vasopressin and epinephrine vs. epinephrine alone
Table 2. Significant outcomes for combined vasopressin and epinephrine treatment
RR (95% CI) pvalue

32. ROSC[37]
Survival to hospital admission[38]
In subgroup: PEA[38]
In subgroup: Collapse to ED arrival time of 15–30
minutes[38]
In subgroup: Collapse to ED arrival time of 30–45
minutes[38]
Survival to hospital discharge[37]
1.42 (1.141.77)
1.42 (1.022.04)
1.30 (0.902.06)
1.22 (1.011.49)
1.11 (1.001.24)
3.69 (1.528.95)
0.05
0.02
0.05
0.05
There is no current evidence of significant survival benefit with improved
neurological outcomes in patients given combinations of both epinephrine and
vasopressin during cardiac arrest.[32][35][39][40] A systematic review from 2008 did,
however, find one study that showed a statistically significant improvement in ROSC
and survival to hospital discharge with this combination treatment; unfortunately,
those patients that survived to hospital discharge had overall poor outcomes and many
suffered permanent, severe neurological damage.[37][40] A more recently published
clinical trial out of Singapore has shown similar results, finding combination
treatment to only improve the rate of survival to hospital admission, especially in the
subgroup analysis of patients with longer "collapse to emergency department" arrival
times of 15 to 45 minutes.[38] Table 2 lists all statistically significant findings of a
correlation between combined treatment and positive outcomes found in these two
studies.
2010 American Heart Association Guidelines
The 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation
and Emergency Cardiovascular Care recommend the consideration of vasopressor
treatment in the form of epinephrine in adults with cardiac arrest (Class IIb, LOE A
recommendation).[41] Due to the absence of evidence that vasopressin administered
instead of or in addition to epinephrine has significant positive outcomes, the
guidelines do not currently contain vasopressin as a part of the cardiac arrest
algorithms.[41] It does, however, allow for one dose of vasopressin to replace either the
first or second dose of epinephrine in the treatment of cardiac arrest (Class IIb, LOE
A recommendation).[41]
Vasopressin receptor inhibition
Main article: vasopressin receptor antagonist
A vasopressin receptor antagonist is an agent that interferes with action at the
vasopressin receptors. They can be used in the treatment of hyponatremia.[42]
See also

33. Oxytocin
Sexual motivation and hormones
Vasopressin receptor
Vasopressin receptor antagonists
Copeptin