Slow Onset of Activation and Delay of Inactivation in Transient Current of Nitella axilliformis

概要

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Single membrane samples of Nitella axilliformis, in which major parts of vacuoles were removed, were prepared by centrifugation and ligation with threads. Voltage clamp experiments were made with the samples, proving that the transient current occurs only after a initial delay as was observed in Chara corallina by Beilby and Coster [(1979) Aust. J. Plant Physiol. 6 : 337]. The membrane potential measured at a corner of the sample exhibited practically the same time course as the membrane potential at the center which changed stepwise, indicating that the delay is not related to the propagation of the potential change. The delay did not change sensitively to ionic strength of the external solution, suggesting that it is not caused by low electric conductance around the sample but is related to the gating mechanism of Cl channel. Various models were examined to explain the time course of the transient current. The best agreement was obtained by introducing a delay δ_h in inactivation with the expression of I_<Cl>=<g^^->_<Cl>m^8h(V_M-V_<Cl>), where I_<Cl> stands for the transient current and V_M is the clamp potential, and <g^^->_<Cl>= 15 mS・cm^<-2>, V_<Cl>= -31.5 mV. The delay δ_h decreases similarly to τ_m with increasing V_M, suggesting that inactivation starts after activation proceeds.
日本植物生理学会の論文