Regulation of [K.sub.ATP] channels by [P.sub.2Y] purinoceptors coupled to PI[P.sub.2] metabolism in guinea pig ventricular cells

Regulation of [K.sub.ATP] channels by [P.sub.2Y] purinoceptors coupled to PI[P.sub.2] metabolism in guinea pig ventricular cells. Am J Physiol Heart Circ Physiol 282: H757-H765, 2002. First published October 11, 2001; 10.1152/ ajpheart.00246.2001.--We used patch-clamp techniques to elucidate the regulatory mechanisms of ATP-sensitive [K.sup.+] ([K.sub.ATP]) channels by stimulation of [P.sub.2] purinoceptors in guinea pig ventricular myocytes. Extracellular ATP at 0.1 mM transiently inhibited by 90.5 [+ or -] 5.0% the whole cell [K.sub.ATP] channel current evoked by a reduction in intracellular ATP concentration to 0.5 mM and exposure to 30 [micro]M pinacidil. ADP and AMP (both 1 mM) also decreased the current by 42.8 [+ or -] 9.3% and 9.4 [+ or -] 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 [micro]M staurosporine or 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid in the pipette. In the presence of 10 [micro]M wortmannin or the absence of ATP in the cytosol, the ATP-induced channel inhibition was irreversible. Phosphatidylinositol 4,5-bisphosphate (PI[P.sub.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 [micro]M 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.sub.ATP] channels is modulated by extracellular ATP by a mechanism involving [P.sub.2Y] purinoceptors coupled to GTP-binding proteins associated with reduction of the sarcolemmal PI[P.sub.2] concentration via stimulation of phospholipase C. phosphatidylinositol 4,5-bisphosphate, extracellular adenosine 5'-triphosphate; phosphatidylinositol turnover; phospholipase C