Abstract
Physiological activity of G protein gated inward rectifier K(+) (GIRK, Kir3) channel, dynamically regulated by three key ligands, phosphoinositol-4,5-bisphosphate (PIP(2)), Gβγ, and Na(+), underlies cellular electrical response to multiple hormones and neurotransmitters in myocytes and neurons. In a reducing environment, matching that inside cells, purified GIRK2 (Kir3.2) channels demonstrate low basal activity, and expected sensitivity to the above ligands. However, under oxidizing conditions, anomalous behavior emerges, including rapid loss of PIP(2) and Na(+)-dependent activation and a high basal activity in the absence of any agonists, that is now paradoxically inhibited by PIP(2). Mutagenesis identifies two cysteine residues (C65 and C190) as being responsible for the loss of PIP(2) and Na(+)-dependent activity and the elevated basal activity, respectively. The results explain anomalous findings from earlier studies and illustrate the potential pathophysiologic consequences of oxidation on GIRK channel function, as well as providing insight to reversed ligand-dependence of Kir and KirBac channels.