Goldman Equation - Equation For Monovalent Ions

Equation For Monovalent Ions

The GHK voltage equation for monovalent positive ionic species and negative:

This results in the following if we consider a membrane separating two -solutions:

It is "Nernst-like" but has a term for each permeant ion. The Nernst equation can be considered a special case of the Goldman equation for only one ion:

• = The membrane potential (in volts, equivalent to joules per coulomb)
• = the permeability for that ion (in meters per second)
• = the extracellular concentration of that ion (in moles per cubic meter, to match the other SI units)
• = the intracellular concentration of that ion (in moles per cubic meter)
• = The ideal gas constant (joules per kelvin per mole)
• = The temperature in kelvins
• = Faraday's constant (coulombs per mole)

The first term, before the parenthesis, can be reduced to 61.5 mV for calculations at human body temperature (37 °C)

Note that the ionic charge determines the sign of the membrane potential contribution.

The usefulness of the GHK equation to electrophysiologists is that it allows one to calculate the predicted membrane potential for any set of specified permeabilities. For example, if one wanted to calculate the resting potential of a cell, they would use the values of ion permeability that are present at rest (e.g. ). If one wanted to calculate the peak voltage of an action potential, one would simply substitute the permeabilities that are present at that time (e.g. ).