Redox-dependent Gating of G Protein-coupled Inwardly Rectifying K ⁺ Channels

G protein-coupled inwardly rectifying K⁺ channels (GIRK) play a major role in inhibitory signaling in excitable and endocrine tissues. The gating mechanism of these channels is mediated by a direct interaction of the Gβγ subunits of G protein, which are released upon inhibitory neurotransmitter receptor activation. This gating mechanism is further manifested by intracellular factors such as anionic phospholipids and Na ⁺ and Mg²⁺ ions. In addition to the essential role of these components for channel function, phosphorylation events can also modulate channel activity. In this study we explored the involvement of redox modulation on GIRK channel function. Extracellular application of the reducing agent dithiothreitol (DTT), but not reduced glutathione, activated GIRK channels without affecting their permeation or rectification properties. The DTT-dependent activation was found to mimic receptor activation and to act directly on the channel in a membrane delimited fashion. A critical cysteine residue located in the N-terminal cytoplasmic domain was found to be essential for DTT-dependent activation in hetero- and homotetrameric contexts. Interestingly, when mutating this cysteine residue, DTT-dependent activation was abolished, but receptor-mediated channel activation was not affected. These results suggest that intracellular redox potential can play a major role in tuning GIRK channel activity in a receptor-independent manner. This sort of redox modulation can be part of an important cellular protective mechanism against ischemic or hypoxic insults.