EARLY EVENTS IN PLASMA-MEMBRANE OF CHARA-CORALLINA AFTER ELECTRICAL-STIMULATION .1. STUDIES UNDER CURRENT CLAMP CONDITIONS

Events in the early periods of the stimulus-response (current-voltage) relation of Chara corallina internodal cell were studied under curren t clamp conditions. Whenever the internodal cell elicited an action po tential by a current stimulus, the voltage exhibited an additional pea k soon after application of the stimulus; that is, the peak voltage pr eceded the threshold for the action potential. The strength-peak volta ge relation was almost a straight line when the voltage was less negat ive than about -50 mV. The electromotive force at the peak voltage var ied by 48.4 mV between 0.1 and 1.0 mM of external K+ concentration, an d it was within expected range of equilibrium potential for K+ ions. E ven when the action potential was not elicited at a low external Ca2concentration, the peak voltage still appeared, keeping the electromot ive force within the range of equilibrium potential for K+ ions. We co ncluded that the K+ channel opens very early after electrical stimulat ion and when the action potential is elicited under a sufficient exter nal Ca2+ concentration, the entry of external Ca2+ ions necessary for the opening of the Ca2+ activated Cl- channel occurs after the peak vo ltage.