Resting membrane potential, equilibrium potential GHK equation

1. PETER KEVIN NATHAN

2. Resting potential
 electrical potential difference between the inside of the cell and the
surrounding extracellular fluid  membrane potential
 All cells need the MP to carry out various biological processes (nerves and
muscles), because changes in their membrane potentials are used to
code and transmit information.
 When a nerve or muscle cell is at ‘rest’ it’s membrane potential is called
resting membrane potential.

3. Resting potential values in different types of
cells
Cell types Resting potential
Skeletal muscle cells −95 mV
Smooth muscle cells –60 mV
Astroglia –80 to –90 mV
Neurons –60 to –70 mV
Erythrocytes –9 mV
Photoreceptor cells –40 mV

4. Resting potential
 The electrical pot. of the i.c space is always negative compared to the e.c
space because there is an excess of negative charge inside of the cell.
 Equilibrium potential  the net transmembrane flux of an ion (k+) is
zero.
 Nernst eq:
 Eq. potential for k+ is around -89mV. Na+ is around +60mV

5.  Thermodynamic equilibrium (K+)
One k+ comes into the cell, at the same time one k+ goes out of the
cell. Thus no net flux of K+ and the MP does not change.
 Energy is not expended
K+
 Electrochemical equilibrium
 No net transport of charge and no net
flux of chemical gradient. K+ cell

6. Factors determining the resting potential
 Goldman-Hodgkin-Katz voltage equation/diffusion potential, GHK
equation:
 Represents all ion species, most significant contribution.
 concentrations of ions, permeability, conductance of each ion species.
 Not a thermodynamic equilibrium.
 When the permeability of a given ion increases dramatically, the RMP gets
closer to the Eq. pot. of the given ion.

7. Factors determining the resting potential
 Pump Potential
 3Na+ are being pumped out and 2K+ pumped in against their concentration
gradients.
 Requires energy.
 Donnan Potential
 large impermeable negatively charged intracellular molecules (proteins)
attracting positively charged ions (e. g.: Na+ and K+) and repelling negative
ones (e. g.: Cl−)

8. THANK YOU