Problem Set 2, Problem 3

A neuron's internal and external concentrations of potassium, sodium and chloride have been measured. The internal concentration of potassium ions is $168\ \text{mM}$, of sodium ions is $50\ \text{mM}$, and of chloride ions is $41\ \text{mM}$. The external concentration of potassium ions is $6\ \text{mM}$, of sodium ions is $337\ \text{mM}$, and of chloride ions is $340\ \text{mM}$. At rest, $p_{\text{K}^+}:p_{\text{Na}^+}:p_{\text{Cl}^-}$ is $1: 0.019:0.381$.

a.

Predict the resting potential $V_m$ from the Goldman-Hodgkin-Katz equation.

b.

What would be the effect of a tenfold increase in external potassium concentration on the resting membrane potential? What would be the effect of a tenfold decrease in external potassium concentration on the resting membrane potential? Predict the effects using the GHK equation, and confirm your predictions by running the simulation and taking screenshots for your lab notebook (when running the simulation, round the external potassium concentration to the nearest integer). Explain.