Question

What is the membrane potential in millivolts due to Na+ ions if the extracellular concentration of Na+ ions is 142 mM and the intracellular concentration of Na+ ions is 21 mM at 20 degrees Celsius?

I got -48 mV but I wanted to double check my answer (the number and sign) because I wasn't sure if I did it right

Answer 1

Using the Nerst Equation:

E_Na+ = RT/nF ln [Na+]_out/[Na+]_in

Here R = universal gas constant = 2 cal/mol/K

        T = temperature in kelvin = 20 + 273 = 293K

        F = Faradays constant = 2.3 x 104 calV^-1mol^-1

        n =1 (valence of ionic species)

Putting all the value RT/nF = 25mV

First we will convert Ln to log by multiplying with 2.303

2.303x RT/nF = 58mV

[Na+]_out = 142 mM and [Na+]_in = 21mM

E_Na+ = 58 log 142 / 21 = 58 x log6.76 = 58 x 0.83 = 48.1 mV