The P2Y1 receptor is necessary for adenosine 5′-diphosphate-induced platelet aggregation

The human P2Y(1) receptor heterologously expressed in Jurkat cells behaves as a specific adenosine 5'-diphosphate (ADP) receptor at which purified adenosine triphosphate (ATP) is an ineffective agonist, but competitively antagonizes the action of ADP. This receptor is thus a good candidate to be the elusive platelet P2T receptor for ADP. In the present work, we examined the effects on ADP-induced platelet responses of two selective and competitive P2Y(1) antagonists, adenosine-2'-phosphate-5'-phosphate (A2P5P) and adenosine-3'-phosphate-5'-phosphate (A3P5P). Results were compared with those for the native P2Y(1) receptor expressed on the B10 clone of rat brain capillary endothelial cells (BCEC) and for the cloned human P2Y(1) receptor expressed on Jurkat cells. A2P5P and A3P5P inhibited ADPinduced platelet shape change and aggregation (pA(2) = 5) and competitively antagonized calcium movements in response to ADP in fura-2-loaded platelets, B10 cells, and P2Y(1)-Jurkat cells, In contrast, these compounds had no effect an ADP induced inhibition 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 properties suggest that platelets and BCEC share a common P2Y(1) receptor involved in ADP induced aggregation and vasodilation, respectively. This P2Y(1) receptor coupled to the mobilization of intracellular calcium stores was found to be necessary to trigger ADP induced platelet aggregation. The present results, together with data from the literature, also point to the existence of another as yet unidentified ADP receptor, coupled to adenylyl cyclase and responsible for completion of the aggregation response. Thus, the term, P2T, should no longer be used to designate a specific molecular entity. (C) 1998 by The American Society of Hematology.