Effect of Cytoplasmic Ca_ on the Membrane Potential and Membrane Resistance of Chara Plasmalemma

元データ 日本植物生理学会

概要

Effects of cytoplasmic Ca^<2+> on the electrical properties of the plasma membrane were investigated in tonoplast-free cells of Chara australis that had been internally perfused with media, containing either I mM ATP to fuel the electrogenic pump or hexokinase and glucose to deplete the ATP and stop the pump. In the presence of ATP, cytoplasmic Ca^<2+> up to 2.5・10^<-5>M did not affect the membrane potential (about - 190mV), but membrane resistance decreased uniformly with increasing [Ca^<2+>]_i. In the absence of ATP, the membrane potential, which was only about - I 10mV, was depolarized further by raising [Ca^<2+>]_i from 1.4・10^<-6> to 2.5・10^<-5>M. Membrane resistance, which was nearly the twofold that of ATP-provided cells, decreased markedly with an increase in [Ca^<2+>]_i from zero to 1.38・10^<-6>M, but showed no change for further increases. Internodal cells of Nitellopsis obtusa were more sensitive to intracellular Ca^<2+> with respect to membrane potential than were those of Chara australis, reconfirming the results obtained by Mimura and Tazawa (1983). The effect of cytoplasmic Ca^<2+> on the ATP-dependent H^+ efflux was measured. No marked difference in H^+ effluxes was detected between zero and 2.5×10^<-5>M [Ca^<2+>]_i ; but, at 10^<-4> M the ATP_dependent H^+ efflux was almost zero. Ca^<2+> efflux experiments were done to investigate dependencies on [Ca^<2+>]_i and [ATP]_i. The efflux was about 1 pmol cm^<-2> s^<-1> at all [Ca^<2+>]_i concentrations tested (1.38・10^<-6>, 2.5×10^<-5>, 10^<-4>M). This value is much higher than the influx reported by Hayama et al. (1979), and this efflux was independent of [ATP]_i. The possibility of a Ca^<2+>-extruding pump is discussed.

著者

Tazawa Masashi Departlnent Of Biology Faculty Of Science Osaka University
Luhring Hinrich Department of Botany, Faculty of Science, University of Tokyo
Luehring H Department Of Botany Faculty Of Science University Of Tokyo:(present)botanisches Institute Der Unive
Luhring Hinrich Department Of Botany Faculty Of Science University Of Tokyo:(present)botanisches Institute Der Unive

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