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Hinrich Lühring, Masashi Tazawa, Effect of Cytoplasmic Ca2+ on the Membrane Potential and Membrane Resistance of Chara Plasmalemma, Plant and Cell Physiology, Volume 26, Issue 4, June 1985, Pages 635–646, https://doi.org/10.1093/oxfordjournals.pcp.a076952
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Abstract
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 2.5·10−5m. Membrane resistance, which was nearly the twofold that of ATP-provided cells, decreased markedly with an increase in [Ca2+]i from zero to 1.38·10−6m, 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.
