GTP-binding protein Gq mediates muscarinic-receptor-induced inhibition of the inwardly rectifying potassium channel IRK1 (Kir 2.1)

The inwardly rectifying potassium channel IRK1, a member of the Kir 2.0 fam ily, is inhibited by mi muscarinic receptor stimulation. In this study the mechanism of action underlying the muscarinic response was investigated by identification of the subtype of heterotrimeric G-protein involved in trans duction of the signal. tsA201 cells were simultaneously transfected with cD NAs encoding IRK1, mi and the G alpha subunit of either G(q), G(12) or G(13 ). The whole-cell patch-clamp technique was used to study the effects of G- protein transfection. Antibodies generated against the C-terminal regions o f G alpha (q/11) and G alpha (12) were used to confirm G-protein expression by Western blot. When challenged with carbachol, IRK1 currents recorded fr om cells co-transfected with G alpha (q) were potently inhibited compared w ith controls. Conversely, co-transfection with G alpha (12) or G alpha (13) subunits had no effect on muscarinic-receptor-induced inhibition of IRK1. Concentration response curves revealed that carbachol was 16 times more pot ent at inhibiting IRK1 currents in cells co-transfected with G alpha (q) as compared with G alpha (12) co-transfected cells. Immunoblotting illustrate d low levels of endogenous G alpha (q/11) and G alpha (12) in untransfected tsA cells. Transfection with G alpha (q) or G alpha (12) cDNAs greatly inc reased the levels of G-protein expression in both cell populations. G-prote in expression did not interfere with mi muscarinic receptor expression leve ls. These findings suggest that the mi muscarinic-receptor-induced inhibiti on of IRK1 is mediated by the heterotrimeric G-protein, G alpha (q) in tsA cells. (C) 2001 Elsevier Science Ltd. All rights reserved.