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Membranes and Bioenergetics

Characterization of Vacuolar Malate and K⁺ Channels under Physiological Conditions ¹

Centre for Plant Biotechnology, Toronto, Ontario M5S 3B2, Canada, Department of Botany, University of Toronto, Toronto, Ontario M5S 3B2, Canada

Patch-clamp techniques were employed to study the electrical properties of vacuoles from sugar beet (Beta vulgaris) cell suspensions at physiological concentrations of cytoplasmic Ca²⁺. Vacuoles exposed to K⁺ malate revealed the activation of instantaneous and time-dependent outward currents by positive membrane potentials. Negative potentials induced only instantaneous inward currents. The time-dependent outward currents were 10 times more selective for malate than for K⁺ and were completely blocked by zinc. Vacuoles exposed to KCl developed instantaneous currents when polarized to positive or negative membrane potentials. The time-dependent outward channels could serve as the route for the movement of malate into the vacuole, whereas K⁺ could move through the time-independent inward and outward channels.

¹ This research was supported by an operating grant of the Natural Sciences and Engineering Council of Canada to E.B.

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