To understand better, consider a cell with only two permeant ions, potassium and sodium.

It is "Nernst-like" but has a term for each permeant ion.

In the example diagram here, the model cell was given only one permeant ion (potassium).

The more ions are permeant, the more complicated it becomes to predict the membrane potential.

These molecules are known as permeant molecules.

First medical application of electroporation was used for introducing poorly permeant anticancer drugs into tumor nodules.

Permeability depends on the temperature of the interaction as well as the characteristics of both the polymer and the permeant component.

The Gibbs-Donnan equation at equilibrium states (assuming permeant ions are Na and Cl):

The presence of a charged impermeant ion (for example, a protein) on one side of a membrane will result in an asymmetric distribution of permeant charged ions.

What the GHK equations says, basically, is that at any time, the value of the membrane potential will be a weighted average of the equilibrium potentials of all permeant ions.

Each of these variables can attain a value between 1 (fully permeant to ions) and 0 (fully non-permeant), the product of these variables yielding the percentage of conducting channels.

The amount of sodium and potassium the channels allow through their pores (their conductance) varies from 50-110 pS, with the conductance depending on the specific subunit composition as well as the permeant ion.

Lymphocytes can be activated using a combination of a phorbol ester or a permeant DAG analogue to activate PKC and an ionophore to mimic the calcium-mobilizing action of InsP 3.

This potential is predicted, in theory, either by the Nernst equation (for systems of one permeant ion species) or by the Goldman-Hodgkin-Katz equation (for more than one permeant ion species).

If the membrane were to become permeable to a type of ion that is more concentrated on one side of the membrane, then that ion would contribute to membrane voltage because the permeant ions would move across the membrane with net movement of that ion type down the concentration gradient.