The Goldman–Hodgkin–Katz voltage equation, used in cell membrane physiology, can be written

The GHK equation is used to determine the resting membrane potential in real cells. It is a generalization of the Nernst equation. This Demonstration shows the Goldman–Hodgkin–Katz voltage function, plotted in gray, in terms of the argument :

, where

is the membrane potential in volts;

is the ideal gas constant in joules per kelvin-mol;

is the temperature (Kelvin);

is Faraday's constant in coulombs/mol;

, , are the permeabilities of the potassium, sodium, and chloride ions;

, , are the extracellular concentrations of potassium, sodium, and chloride;

, , are their intracellular concentrations.

Also shown are the derivatives of the GHK function (red) and the Nernst function (green), . The region between the GHK and Nernst functions is shown filled.