THE P2Y(1) RECEPTOR IS NECESSARY FOR ADENOSINE 5'-DIPHOSPHATE-INDUCEDPLATELET-AGGREGATION

The human P2Y(1) receptor heterologously expressed in Jurkat cells beh aves as a specific adenosine 5'-diphosphate (ADP) receptor at which pu rified adenosine triphosphate (ATP) is an ineffective agonist, but com petitively antagonizes the action of ADP. This receptor is thus a good candidate to be the elusive platelet P2T receptor for ADP. In the pre sent work, we examined the effects on ADP-induced platelet responses o f two selective and competitive P2Y(1) antagonists, adenosine-2'-phosp hate-5'-phosphate (A2P5P) and adenosine-3'-phosphate-5'-phosphate (A3P 5P). Results were compared with those for the native P2Y(1) receptor e xpressed on the B10 clone of rat brain capillary endothelial cells (BC EC) and for the cloned human P2Y(1) receptor expressed on Jurkat cells . A2P5P and A3P5P inhibited ADPinduced platelet shape change and aggre gation (pA(2) = 5) and competitively antagonized calcium movements in response to ADP in fura-2-loaded platelets, B10 cells, and P2Y(1)-Jurk at cells, In contrast, these compounds had no effect an ADP induced in hibition of adenylyl cyclase in platelets or B10 cells, whereas known antagonists of platelet activation by ADP such as Sp-ATP alpha S were effective. These identical signaling responses and pharmacologic prope rties suggest that platelets and BCEC share a common P2Y(1) receptor i nvolved in ADP induced aggregation and vasodilation, respectively. Thi s P2Y(1) receptor coupled to the mobilization of intracellular calcium stores was found to be necessary to trigger ADP induced platelet aggr egation. The present results, together with data from the literature, also point to the existence of another as yet unidentified ADP recepto r, coupled to adenylyl cyclase and responsible for completion of the a ggregation response. Thus, the term, P2T, should no longer be used to designate a specific molecular entity. (C) 1998 by The American Societ y of Hematology.