Opposing effects of aluminum on inward-rectifier potassium currents in bean root-tip protoplasts.
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.
Etherton
B
B
Department of Pharmacology, University of Vermont, College of Medicine, Given Building, Burlington, VT 05405-0068, USA. bud.etherton@uvm.edu
Heppner
T J
TJ
Cumming
J R
JR
Nelson
M T
MT
D000535:Aluminum / Q000494:pharmacology*; D002478:Cells, Cultured; D004306:Dose-Response Relationship, Immunologic; D004351:Drug Resistance / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D027805:Phaseolus / Q000187:drug effects / Q000502:physiology*; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000502:physiology*; D011523:Protoplasts / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000378:metabolism
D024661:Potassium Channels, Inwardly Rectifying; D012964:Sodium; D000535:Aluminum; D011188:Potassium