Electrogenic Pump Current and ATP-Dependent H+ Efflux Across the Plasma Membrane of Nitellopsis obtusa |
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Authors: | Takeshige Kazuhiko; Shimmen Teruo; Tazawa Masashi |
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Institution: | Department of Botany, Faculty of Science, University of Tokyo Hongo, Tokyo 113, Japan |
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Abstract: | The correlation between the pump current and the ATP-dependentH+ efflux was examined in internodal cells of Nitellopsis obtusa.To control the cytoplasmic pH and ATP concentration, the tonoplastwas removed by intracellular perfusion with an EGTA-containingmedium. Two groups of perfused cells were prepared, one with1 mM ATP (+ATP cells) and the other without ATP but with hexokinaseand glucose (ATP cells). The ATP-dependent H+ effluxwas calculated as the difference in H+ efflux between the +ATPand ATP cells. Based on an electrically equivalent circuitmodel of the plasma membrane, the pump current was calculatedfrom the membrane potentials and the membrane resistances ofboth +ATP and ATP cells. When the membrane potentialwas not too high (220 mV), the ATP-dependent H+ current(19 mA m2) was almost equal to the pump current (20 mAm2) calculated from the electrical data. This indicatesthat the electrogenic pump current across the plasma membraneof Nitellopsis obtuse was mostly carried by H+. But when themembrane potential was high (280 mV), the H+ currentwas lower than the pump current. The possible cause of thisdiscrepancy is discussed. (Received November 5, 1984; Accepted February 28, 1985) |
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