Oxidation driven reversal of PIP2-dependent gating in GIRK2 channels.

Abstract

Physiological activity of G protein gated inward rectifier K+ (GIRK, Kir3) channel activity is dynamically regulated by three key ligands, phosphoinositol-4,5-bisphosphate (PIP2), Gβγ, and Na+, which 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 demonstrated low basal activity, and appropriate sensitivity to the above ligands. However, under oxidizing conditions, anomalous behavior emerged, including rapid loss of agonist dependent activation, and high basal activity in the absence of any agonists that was paradoxically inhibited by PIP2. Mutagenesis identified two cysteine residues as being responsible for the loss of agonist dependent activation 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 gating in related Kir and KirBac channels.