Regulation of K(ATP) channels by P(2Y) purinoceptors coupled to PIP(2) metabolism in guinea pig ventricular cells.

We used patch-clamp techniques to elucidate the regulatory mechanisms of ATP-sensitive K(+) (K(ATP)) channels by stimulation of P(2) purinoceptors in guinea pig ventricular myocytes. Extracellular ATP at 0.1 mM transiently inhibited by 90.5 +/- 5.0% the whole cell K(ATP) channel current evoked by a reduction in intracellular ATP concentration to 0.5 mM and exposure to 30 microM pinacidil. ADP and AMP (both 1 mM) also decreased the current by 42.8 +/- 9.3% and 9.4 +/- 4.8%, respectively, but adenosine did not, even at 10 mM. ATP-induced channel inhibition was hardly observed in the presence of 0.2 mM suramin, 0.2 mM guanosine 5'-O-(2-thiodiphosphate), or 0.1 mM compound 48/80, whereas it was not influenced by the presence of 0.1 microM staurosporine or 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid in the pipette. In the presence of 10 microM wortmannin or the absence of ATP in the cytosol, the ATP-induced channel inhibition was irreversible. Phosphatidylinositol 4,5-bisphosphate (PIP(2)) at 0.1 mM in the outside-out patch pipette prevented ATP-induced channel inhibition. The half-maximal internal ATP concentrations for inhibition of channel activity determined in inside-out membrane patches were 13.8 microM in the presence and 1.12 mM in the absence of 0.1 mM ATP at the external side. It is concluded that activity of K(ATP) channels is modulated by extracellular ATP by a mechanism involving P(2Y) purinoceptors coupled to GTP-binding proteins associated with reduction of the sarcolemmal PIP(2) concentration via stimulation of phospholipase C.