Effects of Extracellular Calcium on fASIC1 Currents
Abstract: Fish ASIC1 (fASIC1) cloned from Opsanus tau, unlike the rat ASICs, requires Ca2+ in the extracellular preconditioning solution (pH 7.4) to be activated. Here we show that fASIC1 is interacting with Ca2+ in the same way as mammalian ASICs: extracellular Ca2+ is increasing the proportion of channels available for activation by stabilizing the closed state of the channel; in the activation process Ca2+ is released; H+ compete for the binding site of Ca2+ making the gating mechanism both Ca2+ and H+ dependent; H+ stabilizes the desensitized state; Ca2+ blocks the fASIC1 channel; and the affinity of the block is also modulated by H+. The Ca2+ activation requirement of fASIC1 reflects its greater affinity for steady-state desensitization by H+ compared to mammalian ASIC1.
asic opsanus tau desensitization /deg/enac protons channel block