Current-voltage relationships of a sodium-sensitive potassium channel in the tonoplast ofChara corallina |
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Authors: | Adam Bertl |
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Institution: | (1) Pflanzenphysiologisches Institut und Botanischer Garten der Universität Göttingen, D-3400 Göttingen, Federal Republic of Germany;(2) Present address: Department of Cellular and Molecular Physiology, Yale University, School of Medicine, 333 Cedar Street, 06510 New Haven, CT |
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Abstract: | Summary The membrane of mechanically prepared vesicles ofChara corallina has been investigated by patch-clamp techniques. This membrane consists of tonoplast as demonstrated by the measurement of ATP-driven currents directed into the vesicles as well as by the ATP-dependent accumulation of neutral red. Addition of 1mm ATP to the bath medium induced a membrane current of about 3.2 mA·m–2 creating a voltage across the tonoplast of about –7 mV (cytoplasmic side negative). On excised tonoplast patches, currents through single K+-selective channels have been investigated under various ionic conditions. The open-channel currents saturate at large voltage displacements from the equilibrium voltage for K+ with limiting currents of about +15 and –30 pA, respectively, as measured in symmetric 250mm KCl solutions. The channel is virtually impermeable to Na+ and Cl–. However, addition of Na+ decreases the K+ currents. TheI–V relationships of the open channel as measured at various K+ concentrations with or without Na+ added are described by a 6-state model, the 12 parameters of which are determined to fit the experimental data. |
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Keywords: | Chara corallina tonoplast K+ channel Na+ effect cyclic model |
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