Potassium and Chloride Effluxes during Excitation of Characeae Cells

Abstract

Action potentials of intact and tonoplast-free Characeae cells were studied in relation to the effluxes of K$ and Cl-. K$ efflux was monitored by atomic absorption spectroscopy or direct measurement of 42K efflux. Cl- efflux was monitored by the Ag-AgCl electrode method. A large K$ efflux was always observed during excitations irrespective of whether the cell was intact or tonoplast-free. In tonoplast-free cells, the permeability of the plasma membrane for K$ at the plateau of the prolonged action potential was almost the same as that in the resting state. In many cases, Cl- efflux was also observed during excitations of intact cells although some cells showed action potentials without a detectable increase in Cl- efflux. Almost all tonoplast-free cells generated action potentials with no associated increase in Cl- efflux. These results indicate that some ion other than Cl- carries inward current which balances the outward current carried by K$. Calcium ion is discussed as the most probable candidate.