Membrane Potential Discussion Notes

a cell is at equilibirum potential when:

delta G = 0

Nernst Equation

van’t Hoff’s equation with membrane potential taken into account

                                                    i.     deltaG = RTln(S outside/S inside) + zFE

in the Nerst equation, z is equal to:

an ion’s valence

in the Nerst equation, F is equal to:

the faraday constant

in the Nernst equation, E is equal to:

membrane potential

the Nerst equation can be rearranged to solve for E, which looks like:

1.     E ion = (61mV/z) x log([s]outside/[s]inside)

The equilibrium potential for potassium is -94mV. This means that:

when the inside of the cell is -94mV, it will arrest movement of potassium. deltaG=0

what else must we take into account when evaluating diffusion of a substance through a membrane?

resting membrane potential/permeability differences between ions

Goldman H K equation normalized the Nernst equation based on the permeabilities of both ions:

a.     The 0.04 accounts for potassium being 25x more permeable than sodium (1/25)

b.     Vm = 61log (PNa[Na]o) + (PK[K]o) / (PNa[Na]i) + (PK[K]i)

c.      Vm = 61log (0.04)(145mM) + (1)(4mM) / (0.04)(15mM) + (1)(140mM)

d.     Vm = -70.6mV

                                                    i.     It will favor potassium because potassium is more permeable