Plasma membrane Ca²⁺ channels in roots of higher plants and their role in aluminium 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 m M 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 μM extracellular verapamil (a Ca²⁺ channel antagonist). Extracellular AlCl₃ (70 μM, pH 4.9) almost completely blocked the channel.