Resting membrane potential

1. Resting Membrane Potential
Dr. Sara Sadiq
(MBBS, M.Phil)

2. Channels in Cell Membrane
1. K-Na leak channels  leak towards conc: gradients
2. Voltage gated Na+ Channels  remain closed at normal RMP
3. Voltage gated K+ Channels  remain closed at normal RMP
4. Slow Ca- Na Channels  only in Cardiac & Smooth muscles

3. Pumps in Cell Membrane
1. Na- K Electrogenic pump
2. Ca+ pump

4. Resting Membrane Potential
• Membrane Potential of nerve fiber when it is not
transmitting signals or in resting condition
• Normal RMP: -90mv

5. The membrane potential is due to the
sodium ions found in the extracellular
matrix and the potassium ions found in the
intracellular matrix
A cell is
“polarized”
because the
interior (ICF)
side of the
membrane
is relatively
more negative
than the
exterior (ECF).

6. Major Players in Resting Potential
• Na+ and K+ Leaky channels

7. Basics of Membrane Potentials
• Diffusion potential (By passive diffusion of Na and K)
• Equilibrium potential (By active diffusion i.e Na-K ATPase pump)

9. Maintenance of RMP
1. Diffusion potential
• K+ conc inside = 140mEq/L
• K+ conc outside = 4mEq/L
• Diffuses out until membrane potential becomes -94mv
• -94mv prevents further outflux of potential  Nernst potential for K+

10. Maintenance of RMP
1. Diffusion potential
• Na+ conc inside = 14 mEq/L
• Na+ conc outside = 142 mEq/L
• Diffuses inside until membrane potential becomes +61mv
• +61mv prevents further influx of potential  Nernst potential for Na+
• Na-K leak channel is 100 times less permeable to Na+ than K+
• So diffusion potential for Na+ is +8mv

12. Maintenance of RMP
2. Na-K Electrogenic pump
• 3 Na+ ions move out
• 2 K+ ions move in
• Creating negativity inside cell membrane  -4mv

13. Na-K ATPas Pump

14. Net Resting Membrane Potential
• K+ diffusion potential = -94 mv
• Na+ diffusion potential = +8mv
• Na-K electrogenic pump = -4mv
• Net RMP = -90mv

15. Why negativity inside cell
• Proteins and organic compounds can’t diffuse out of cell

16. Nernst Potential
• Potential difference across cell membrane that can block further
diffusion of ions towards concentration gradients
• -94 mv completely block K+ diffusion towards conc: gradient i.e
inside to outside

17. Nernst Equation
• For any univalent ion at body temperature of 37° C
• EMF (mV)= +/-61log (Conc: inside)
(Conc: outside)

18. For Sodium
• If Nao = 142 mM and Nai = 14 mM
EK = -61 log(14/142)
EK = -61 log(0.1)
EK = +61 mV

19. For potassium
• If Ko = 5 mM and Ki = 140 mM
EK = -61 log(140/4)
EK = -61 log(35)
EK = -94 mV

20. Goldman- Hodgkin Equation
EMF (mv) = -61 x log C(Na)i + P(Na) + C(K)i + P(K) + C(Cl)o - P(Cl)
C(Na)o + P(Na) + C(K)o + P(K) + C(Cl)i - P(Cl)
• Na diffusion potential  -86mv
• K diffusion potential  -94mv
• Permeability of Cl does not change greatly

21. Factors Affecting Nernst Potential
• 3 factors
• Polarity of each ion
• Membrane permeability of the ions
• Concentrations of respective ions on both sides: (i= inside), (o= outside)