Homeostatic Regulation of Membrane Potential by an Electrogenic Ion Pump against Change in the K^+ Concentration of the Extra- and Intra-Organ Perfusion Solutions

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The dependence of membrane potentials on changes in the extra-cellular k^+ concentration [k^+]_e was investigated in potato tuber slices with dripping perfusion, and in growing Vigna hypocotyl segments with pressurized intra-organ perfusion methods. Only under anoxia were the membrane potential of potato tuber slices and the electric potential difference between the parenchyma symplast and xylem (V_<px>) of Vigna hypocotyl segments depolarized markedly (46 mV and 42 mV/log[k^+]_e unit, respectively) with increasing [k^+]_e above the critical values. The electric potential difference between the parenchyma symplast and organ surface (V_<px>) of the hypocotyl segments remained nearly unchanged up to 30 mEq [k^+]_e. Under highly aerobic conditions the membrane potentials were relatively independent of [k^+]_e except at very high k^+ concentrations. V_<px> showed even hyperpolarization with the increasing KCl concentration in the perfusion solution that is not in direct contact with the surface membrane of the parenchyma symplast. The respiration-dependent electrogenic components of the membrane potentials regularly increased with the increasing [k^+]_e. A voltage-dependent homeostatic control of membrane potential is discussed.
日本植物生理学会の論文