PLASMA-MEMBRANE CA2+ CHANNELS IN ROOTS OF HIGHER-PLANTS AND THEIR ROLE IN ALUMINUM TOXICITY

Single Ca2+ channel records were obtained from plasma membrane-enriched fractions of wheat roots incorporated into artificial planar lipid bilayers. The channel had a unitary conductance of 15 pS for a 10 to 95 mM CaCl2 gradient (cytoplasm: outside of the cell). The voltage dependence displayed by the channel agreed with that expected for Ca2+ channels in the plasma membrane. The channel gating was strongly modified by addition of 20 mu M extracellular verapamil (a Ca2+ channel antagonist). Extracellular AlCl3 (70 mu M, PH 4.9) almost completely blocked the channel.