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Opposing effects of aluminum on inward-rectifier potassium currents in bean root-tip protoplasts.
Etherton B, Heppner T, Cumming J, Nelson MT
Journal of Membrane Biology. 2004;198( 1):15-22.
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Abstract
Inward currents in root cap protoplasts of the aluminum-tolerant cultivar, Dade, of Phaseolus vulgaris L. were investigated using the whole-cell patch-clamp technique. The properties of these currents were similar to those seen in inward rectifying K+ channels in other plant tissues. Replacing bath K+ with Na+ nearly abolished the observed currents. Higher bath K+ concentrations increased inward currents. AlCl3 in pH 4.7 bath solutions caused inward K+ currents to activate more rapidly and at more positive voltages when compared with AlCl3 free solutions. In 10 microM AlCl3 the activated inward K+ currents were significantly larger than in the AlCl3-free solution at all voltages except at the most negative voltage of -174 mV and the least negative of -74 mV. In contrast, in 80 microM Al3+, when hyperpolarizing voltages were most negative, the inward K+ currents were inhibited relative to the currents in 10 microM AlCl3. Enhancement of inward K+ currents by AlCl3 is consistent with Al3+ binding to the external surface of the root cap protoplast, decreasing the surface charge, thus causing the channels to sense a more negative membrane potential. Inhibition of inward K+ currents with higher AlCl3 concentrations and more negative voltages is consistent with Al3+ block of K+ channels.
Keyword(s)
Cells, Cultured; Dose-Response Relationship, Immunologic; drug effects: Ion Channel Gating; drug effects: Membrane Potentials; drug effects: Phaseolus; drug effects: Plant Roots; drug effects: Potassium Channels, Inwardly Rectifying; drug effects: Protoplasts; metabolism: Potassium; metabolism: Sodium; pharmacology: Aluminum; physiology: Drug Resistance