Potassium and Chloride Effluxes during Excitation of Characeae Cells

Action potentials of intact and tonoplast-free Characeae cellswere studied in relation to the effluxes of K^$ and Cl^-. K^$ effluxwas monitored by atomic absorption spectroscopy or direct measurementof ⁴²K efflux. Cl^- efflux was monitored by the Ag-AgCl electrodemethod. A large K^$ efflux was always observed during excitations irrespectiveof whether the cell was intact or tonoplast-free. In tonoplast-freecells, the permeability of the plasma membrane for K^$ at theplateau of the prolonged action potential was almost the sameas that in the resting state. In many cases, Cl^- efflux wasalso observed during excitations of intact cells although somecells showed action potentials without a detectable increasein Cl^- efflux. Almost all tonoplast-free cells generated actionpotentials with no associated increase in Cl^- efflux. Theseresults indicate that some ion other than Cl^- carries inwardcurrent which balances the outward current carried by K^$. Calciumion is discussed as the most probable candidate. (Received November 18, 1983; Accepted June 12, 1984)