Inhibition of a Background Potassium Channel by Gq Protein α-Subunits

Two-pore-domain K⁺ channels provide neuronal background currents that establish resting membrane potential and input resistance; their modulation provides a prevalent mechanism for regulating cellular excitability. The so-called TASK channel subunits (TASK-1 and TASK-3) are widely expressed, and they are robustly inhibited by receptors that signal through Gαq family proteins. Here, we manipulated G protein expression and membrane phosphatidylinositol 4,5-bisphosphate (PIP₂) levels in intact and cellfree systems to provide electrophysiological and biochemical evidence that inhibition of TASK channels by Gαq-linked receptors proceeds unabated in the absence of phospholipase C (PLC) activity, and instead involves association of activated Gαq subunits with the channels. Receptor-mediated inhibition of TASK channels was faster and less sensitive to a PLCβ1-ct minigene construct than inhibition of PIP₂-sensitive Kir3.4(S143T) homomeric channels that is known to be dependent on PLC. TASK channels were strongly inhibited by constitutively active Gαq, even by a mutated version that is deficient in PLC activation. Receptor-mediated TASK channel inhibition required exogenous Gαq expression in fibroblasts derived from Gαq/11 knockout mice, but proceeded unabated in a cell line in which PIP₂ levels were reduced by regulated overexpression of a lipid phosphatase. Direct application of activated Gαq, but not other G protein subunits, inhibited TASK channels in excised patches, and constitutively active Gαq subunits were selectively coimmunoprecipitated with TASK channels. These data indicate that receptor-mediated TASK channel inhibition is independent of PIP₂ depletion, and they suggest a mechanism whereby channel modulation by Gαq occurs through direct interaction with the ion channel or a closely associated intermediary.