Dependence of the acid-sensitive ion channel, ASIC1a, on extracellular Ca2+ ions

Abstract The early H + -induced current in the embryonic spinal cord neurone depends on extracellular Ca 2+ for its function. We have studied the Ca 2+ -dependence of homo- and heteromultimeric acid-sensing ion channels (ASICs) expressed in Cos cells. It was found that single-channel conductance of both the ASIC2a and the ASIC1a channel is reduced at membrane potentials more negative than −40 mV by elevated extracellular Ca 2+ . Due to this effect on unitary currents, the macroscopic ASIC2a peak current at −60 mV decreases gradually with rising extracellular Ca 2+ concentration. In addition, the macroscopic ASIC1a current is very small at low extracellular Ca 2+ and increases with rising Ca 2+ up to 5 mM before decreasing again at still higher concentrations of extracellular Ca 2+ .