Question

Given a cell membrane with the following parameters-

Ion	Extracellular concentration (mmol/L)	Intracellular concentration (mmol/L)	Permeability
K+	10	150	1
Na+	140	15	0.04
Cl-	100	7	0.45

calculate the membrane potential of the cell in mV. (Round your answer to the nearest hundredth.) Assume standard temperature and pressure.

Answer 1

Membrane potential can be caluculated by using nernst equation, so resting potential can be caluculated by summation of each individual ions equlibrium potential, depending upon each ions permeablity

Nernst equation = RT/ZF*log concentration outside/concentration inside

RT/F = 61

Z= correct charge of the ion, in case of K = +1, Na = +1 and Cl = -1

Membrane potential for potassium = 61* log 10/150 = 61* log 0.666 = 61*-1.180 = -72mV.

Membrane potential for sodium = 61*log 140/15 = 61*log 9.333 = 61*0.97 = +59mV

Membrane potential for chloride = 61*log100/7 = 61*log 14.28 = 61*1.15 = -70mV (for Cl, Z= -1)

Now to caluculate the membrane potential of the cell, we have to multiply membrane potential of each cell and permeablity,

for potassium = -72mV*1 = -72mV

for sodium = +59 mV*0.04 = +2.36mV

for chloride + -70 * 0.45 = -31.5mV, by adding up we get the membrane potential

membrane potential of cell = -101mV