Electrogenic properties of the sodium pump in a dynamic model of membrane transport

The general purpose of this theoretical work is to contribute to understand the physiological role of the electrogenic properties of the sodium pump, by studying a dynamic model that integrates diverse processes of ionic and water transport across the plasma membrane. For this purpose, we employ a mathematical model that describes the rate of change of the intracellular concentrations of Na+, K+ and Cl-, of the cell volume, and of the plasma membrane potential (Vm). We consider the case of a nonexcitable, nonpolarized cell expressing the sodium pump; Na+, K+, Cl- and water channels, and cotransporters of KCl and NaCl in its plasma membrane. We particularly analyze here the conditions under which the physiological Vm can be generated in a predominantly electrogenic fashion, as a result of the activity of the sodium pump. A major conclusion of this study is that, for the cell model considered, a low potassium permeability is not a sufficient condition for a predominantly electrogenic generation of the Vm by the sodium pump. The presence of an electroneutral exchange of Na+ and K+ represents a necessary additional requirement.