The origin of bioelectrical potentials in plant and animal cells.

Abstract

Synopsis. The electrical potential difference across a plant or animal cell membrane can be caused by at least three different mechanisms, acting alone or in concert. First, a Donnan equilibrium can account for a sizable membrane potential without the par? ticipation of any active transport process. In a Donnan equilibrium the membrane po? tential is generated by the diffusion of permeating ions down their concentration gradi? ents. The asymmetric distribution of permeating ions is caused by the presence of charged, nondiffusible ions, e.g., proteins inside the cell. The second mechanism is an electrically neutral ion pump, e.g., the coupled sodium-potassium pump found in many types of cells. An electrically neutral pump can generate a large membrane potential if the membrane has a high passive permeability to one of the actively transported ions, usually potassium. The third mechanism is an electrogenic ion pump, which makes a substantial contribution to the membrane potential in several types of plant and ani? mal cells. An electrogenic pump directly causes a net movement of charge across the cell membrane. The membrane voltage generated by the pump then causes a passive flow of diffusible ions which partially short circuits the potential difference generated by the pump.