The influence of plasma membrane electrostatic properties on the stabilityof cell ionic composition

An electro-osmotic model is developed to examine the influence of plasma me mbrane superficial charges on the regulation of cell ionic composition. Ass uming membrane osmotic equilibrium, the ion distribution predicted by Gouy- Chapman-Grahame (GCG) theory is introduced into ion transport equations, wh ich include a kinetic model of the Na/K-ATPase based on the stimulation of this ion pump by internal Na+ ions. The algebro-differential equation syste m describing dynamics of the cell model has a unique resting state, stable with respect to finite-sized perturbations of various types. Negative charg es on the membrane are found to greatly enhance relaxation toward steady st ate following these perturbations. We show that this heightened stability s tems from electrostatic interactions at the inner membrane side that shift resting state coordinates along the sigmoidal activation curve of the sodiu m pump, thereby increasing the pump sensitivity to internal Na+ fluctuation s. The accuracy of electrostatic potential description with GCG theory is p roved using an alternate formalism, based on irreversible thermodynamics, w hich shows that pressure contribution to ion potential energy is negligible in electrostatic double layers formed at the surfaces of biological membra nes. We discuss implications of the results regarding a reliable operation of ionic process coupled to the transmembrane electrochemical gradient of N a+ ions.