Membrane Permeability and Voltage

Abstract

The previous chapters have discussed the various methods by which substances cross cell membranes: (1) diffusion through the lipid membrane itself, (2) diffusion through aqueous pores in the membrane, (3) facilitated transport with the aid of carriers, and (4) active transport with the use of metabolic energy. If the substances involved are charged, the ionic currents involved in any of these methods can generate voltages across the membrane, and these voltages were considered qualitatively at the end of the last chapter. The magnitude of the voltage expected when substances are distributed at equilibrium was also given in Chapter 2. However, many ionic substances are not at equilibrium, and in this chapter more realistic assumptions will be used in deriving the steady voltages normally found across cell membranes.