Regulation of KATP channels by P2Y purinoceptors coupled to PIP2 metabolism in guinea pig ventricular cells

1 First Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Kagoshima 890-8520; and 2 Division of Geriatric Medicine, Akita University School of Medicine, Akita 010-8543, Japan 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 µM 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 µM staurosporine or 10 mM 1,2-bis(2-aminophenoxy)ethane- N,N,N',N' -tetraacetic acid in the pipette. In the presence of 10 µM 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 µM 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. phosphatidylinositol 4,5-bisphosphate, extracellular adenosine 5'-triphosphate; phosphatidylinositol turnover; phospholipase C