Early events in plasma membrane of Chara corallina [Characeae] after electrical stimulation, 1: Studies under current clamp conditions.
1995
Ohkawa T. | Tsutsui I. | Nosaka S.
Events in the early periods of the stimulus-response (current-voltage) relation of Chara corallina internodal cell were studied under current clamp conditions. Whenever the internodal cell elicited an action potential by a current stimulus, the voltage exhibited an additional peak soon after application of the stimulus; that is, the peak voltage preceded the threshold for the action potential. The strength-peak voltage relation was almost a straight line when the voltage was less negative than about -50 mV. The electromotive force at the peak voltage varied by 48.4 mV between 0.1 and 1.0 mM of external K+ concentration, and it was within expected range of equilibrium potential for K+ ions. Even when the action potential was not elicited at a low external Ca(2+) concentration, the peak voltage still appeared, keeping the electromotive force within the range of equilibrium potential for K+ ions. We concluded that the K+ channel opens very early after electrical stimulation and when the action potential is elicited under a sufficient external Ca(2+) concentration, the entry of external Ca(2+) ions necessary for the opening of the Ca(2+) activated Cl(-) channel occurs after the peak voltage.
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