Cysteine 149 in the extracellular finger domain of acid-sensing ion channel 1b subunit is critical for zinc-mediated inhibition.

ABSTRACT

Acid-sensing ion channel 1b (ASIC1b) is a proton-gated Na(+) channel mostly expressed in peripheral sensory neurons. To date, the functional significance of ASIC1b in these cells is unclear due to the lack of a specific inhibitor/blocker. A better understanding of the regulation of ASIC1b may provide a clue for future investigation of its functional importance. One important regulator of acid-sensing ion channels (ASICs) is zinc. In this study, we examined the detailed zinc inhibition of ASIC1b currents and specific amino acid(s) involved in the inhibition. In Chinese hamster ovary (CHO) cells expressing rat ASIC1b subunit, pretreatment with zinc concentration-dependently inhibited the ASIC1b currents triggered by pH dropping from 7.4 to 6.0 with a half-maximum inhibitory concentration of 26 µM. The inhibition of ASIC1b currents by pre-applied zinc was independent of pH, voltage, or extracellular Ca(2+). Further, we showed that the effect of zinc is dependent on the extracellular cysteine, but not histidine residue. Mutating cysteine 149, but not cysteine 58 or cysteine 162, located in the extracellular domain of the ASIC1b subunit abolished the zinc inhibition. These findings suggest that cysteine 149 in the extracellular finger domain of ASIC1b subunit is critical for zinc-mediated inhibition and provide the basis for future mechanistic studies addressing the functional significance of zinc inhibition of ASIC1b.