Regulation of KATP channels by P2Ypurinoceptors coupled to PIP2 metabolism in guinea pig ventricular cells

Abstract

We used patch-clamp techniques to elucidate the regulatory mechanisms of ATP-sensitive K+(KATP) channels by stimulation of P2purinoceptors in guinea pig ventricular myocytes. Extracellular ATP at 0.1 mM transiently inhibited by 90.5 ± 5.0% the whole cell KATP 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 (PIP2) 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 KATP channels is modulated by extracellular ATP by a mechanism involving P2Y purinoceptors coupled to GTP-binding proteins associated with reduction of the sarcolemmal PIP2 concentration via stimulation of phospholipase C.