Abstract
The current/voltage (I/V) relations of the plasma membrane of Chara corallina cells are characteristic when the bathing medium has elevated (5.0 mM) concentrations of potassium. Addition of either 0.5 mM ferricyanide or 0.5mM ferrocyanide usually induced a qualitatively similar increase in the 'leak' current, with a concomitant increase in membrane conductance. Both redox reactants failed for unknown reasons to affect the I/V profile of some of the cells tested. In the sensitive cells, ferricyanide was unable to generate extra current over that found upon addition of ferrocyanide. Because the ferrocyanide oxidation rate of the cells is only 10% of the ferricyanide reduction rate, we conclude that both forms, ferri- and ferrocyanide, 'affect the leak' conductance independent of the redox state of the reactants, i.e. ferrocyanide does not act indirectly via an oxidation to ferricyanide. Hence, under the experimental conditions, we were unable to detect a current that could be assigned to the operation of a transmembrane redox system. Furthermore, the ferri- and ferrocyanide induced shift in the I/V profile only reversed slowly after withdrawal of the redox reactants. This suggests that the elicited current is independent of the presence of an extracellular electron acceptor, i.e. on the continuos operation of a proposed transmembrane redox system.