beta-Adrenergic modulation of maxi-K channels in vascular smooth muscle via G(i) through a membrane-delimited pathway

Direct modulation of large-conductance Ca2+-activated K+ (maxi-K) channel b y receptor-associated G protein in rabbit mesenteric arterial smooth muscle cells was studied using the outside-out patch clamp technique. Applying a beta-adrenoceptor agonist (isoproterenol) increased maxi-K channel activity by 75%, and the effect was almost completely abolished by pretreating the cells with pertussis toxin but not with cholera toxin. When the antibody ag ainst G(i) protein was present in the pipette solution the stimulatory effe ct of isoproterenol disappeared. These results suggest that beta-adrenocept or stimulation increases maxi-K channel activity via a membrane-delimited p athway, probably through pertussis toxin-sensitive G protein (G(i)).