G-protein-gated inwardly rectifying potassium channels regulate ADP-induced cPLA2 activity in platelets through Src family kinases

ADP-induced TXA(2) generation requires the costimulation of P2Y(1), P2Y(12), and the GPIIb/IIIa receptors. Signaling events downstream of the P2Y receptors that contribute to ADIP-induced TXA(2) generation have not been clearly delineated. in this study, we have investigated the role of G-protein-gated inwardly rectifying potassium channels (GIRKs), a recently identified functional effector for the P2Y(12) receptor, in the regulation of ADP-induced TXA(2) generation. At 10-mu M concentrations, the 2 structurally distinct GIRK channel blockers, SCH23390 and U50488H, caused complete inhibition of ADP-Induced cPLA(2) phosphorylation and TXA(2) generation, without affecting the conversion of AA to TXA(2) or ADIP-induced primary platelet aggregation in aspirin-treated platelets. In addition, Src family kinase selective inhibitors abolished 2Me-SADP-mediated cPLA(2) phosphorylation and TXA(2) generation. Furthermore, these GIRK channel blockers completely blocked G(i)-mediated Src kinase activation, suggesting that GIRK channels are upstream of Src family tyrosine kinase activation. In weaver mouse platelets, which have dysfunctional GIRK2 subunits, ADIP-induced TXA(2) generation was impaired. However, we did not observe any defect in 2MeSADP-induced platelet functional responses in GIRK2-null mouse platelets, suggesting that functional channels composed of other GIRK subunits contribute to ADP-induced TXA(2) generation, via the regulation of the Src and cPLA(2) activity.