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Plant and Cell Physiology, 1985, Vol. 26, No. 4 635-646
© 1985

Article

Effect of Cytoplasmic Ca2+ on the Membrane Potential and Membrane Resistance of Chara Plasmalemma

Hinrich Lühring1 and Masashi Tazawa

Department of Botany, Faculty of Science, University of Tokyo Hongo, Tokyo 113, Japan

Effects of cytoplasmic Ca2+ 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 1 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 Ca2+ up to 2.5·10–5 M did not affect the membrane potential (about -190 mV), but membrane resistance decreased uniformly with increasing [Ca2+]i. In the absence of ATP, the membrane potential, which was only about -110 mV, was depolarized further by raising [Ca2+]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 [Ca2+]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 Ca2+ with respect to membrane potential than were those of Chara australis, reconfirming the results obtained by Mimura and Tazawa (1983).

The effect of cytoplasmic Ca2+ on the ATP-dependent H+ efflux was measured. No marked difference in H+ effluxes was detected between zero and 2.5·10–5 M [Ca2+]i; but, at 10–4 M the ATP-dependent H+ efflux was almost zero. Ca2+ efflux experiments were done to investigate dependencies on [Ca2+]i and [ATP]i. The efflux was about 1 pmol cm–2 s–1 at all [Ca2+]i concentrations tested (1.38·10–6, 2.5·10–5, 10–4M). 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 Ca2+-extruding pump is discussed.

1 Present address: Botanisches Institut der Universität Bonn, Venusbergweg 22, 5300 Bonn, F.R.G.

(Received September 22, 1984; Accepted February 19, 1985)
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