3. Physiology
        3.4. General physiology
3.4.2. Resting membrane potential

Resting membrane potential

[Ref: KB2:p232; WG21:p7-8; PK1:p3-4; BL8:p10]

RMP

... is the steady state potential which exists across the cell membrane

Typical values

Production of RMP

  1. Na-K ATPases pump Na+ out of cells and K+ into cells
  2. A concentration gradient across the membrane is produced
  3. Na+ and K+ leak down the gradient
  4. BUT, the membrane is much more permeable to K+, so much more K+ leaves the cell than Na+ enters the cell
  5. This results in net movement of positive charge out of the cell, causing the inside of the cell to be more negative than outside

--> this potential difference is the resting membrane potential

Other contributors

Nernst equation

... calculates the potential difference that any ion (with a concentration gradient across the membrane) would produce if the membrane was permable to it.

E = RT/zF x In{[ion]o/[ion]i}
= 61.5 x log{[ion]o/[ion]i} @37C

Goldman equation

(Full name: Goldman-Hodgkin-Katz form of Nernst equation)

E = 61.5
x log{(PK[K]o+PNa[Na]o+PCl[Cl]o)/(PK[K]i+PNa[Na]i+PCl[Cl]i)}

 

Contribution by ions

An electrolyte have greater influence on RMP when:

Also, as an ion's permeability increases, the membrane potential moves towards its equilibrium potential

Other notes

Nernst equation application

For Cl (i:9-10, o:125)

ECl = -61.5 x log(125/10)
= -61.5 x 1.0969
= -66.91
~ -70mV

For K (i: 135-150, o: 4-5.5)

EK = 61.5 x log(4.5/150)
= 61.5 x -1.523
= -93.66
~ -94mV

For Na (i:10-15, o:145-150)

ENa = 61.5 x log(150/15)
= 61.5 x 1
~ +60mV  

Note

Factors affecting RMP

When extracellular [K+] decreases below 5mM, this small leakage of Na has greater influence on the final RMP. RMP will still become more negative as extracelluar [K+] decreases, but will deviate more from the predicted value (EK)

[BL8:p12]

Keywords:  Goldman equation ; Na-K ATPase pump ; Nernst equation ; Resting membrane potential
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Created20050604
Reviewed20050604


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