Voltage-dependent calcium channels from brain incorporated into planar lipid bilayers.

Many important physiological processes, including neurotransmitter release and muscle contraction, are regulated by the concentration of Ca2+ ions in the cell. Levels of cytoplasmic Ca2+ can be elevated by the entry of Ca2+ ions through voltage-dependent channels which are selective for Ca2+, Ba2+ and Sr2+ ions. We have measured currents through single, voltage-dependent calcium channels from rat brain that have been incorporated into planar lipid bilayers. Channel gating was voltage-dependent: membrane depolarization increased the channel open times and decreased the closed times. The channels were selective for divalent cations over monovalent ions. The well-known calcium channel blockers, lanthanum and cadmium, produced a concentration-dependent reduction of the apparent single-channel conductance. Contrary to expectations, the nature of the divalent cation carrying current through the channel affected not only the single-channel conductance, but also the channel open times, with mean open times being shortest for barium.