The activities of the major ion pathways in the plasma membranes of plants are sensitive to the membrane voltage, V. Therefore, these 'electroenzymes' interact with each other via the free running voltage under physiological conditions. A physical background is given here, of how to calculate these interactions on the basis of experimental data on these electroenzymes. Simplifying model calculations with five major electroenzymes from plant cells (H(+) pump, inward and outward rectifying channels for K(+), a Cl(-) channel, and a 2H(+)/Cl(-) symporter) show that osmotic relations are balanced in the long-term not by an appropriate steady-state, but by alternation between a state of salt uptake at V < < E(K) (the Nernst equilibrium voltage for K(+) diffusion) and a state of salt loss at V > E(K). Several specific properties of the model are discussed numerically, e.g. minimum configuration for oscillations (with two electroenzymes), temperature-compensation, the physiological impact of fast gating in plant membranes, and solution of possible paradoxes, such as flux stimulation by conductance inhibition.