A3P5PS, a P2Y1 receptor antagonist, displaced 27% of ADP analogue binding and inhibited platelet aggregation, demonstrating that P2Y1 activation is essential but not sufficient alone for aggregation.
ADP-induced platelet aggregation requires the simultaneous activation of both the P2Y1 receptor and another low-affinity ADP receptor, as neither can trigger aggregation alone.
ADP acts as an agonist of platelet aggregation via specific receptors which are still to be characterised. Amplification by PCR of a human platelet cDNA library confirmed the presence of mRNA of the P2Y1 receptor in platelets. In order to determine if these P2Y1 receptors were involved in ADP-induced platelet activation, we determined the effects of A3P5PS, an antagonist of the P2Y1 receptor, on the binding of 33P2-MeS-ADP, a potent analogue of ADP. We found that A3P5PS displaced about 27% of 33P2-MeS-ADP binding, a receptor population which has been shown to be resistant to treatment with clopidogrel, a selective anti-ADP agent. A3P5PS specifically inhibited 2-MeS-ADP-induced shape change and calcium increase but did not affect adenylyl cyclase down-regulation. 2-MeS-ADP-induced platelet aggregation was also inhibited by A3P5PS but was restored when platelets were further activated by serotonin, a non-aggregating compound, therefore suggesting that P2Y1-mediated stimulation is an absolute prerequisite for ADP to induce platelet aggregation and a key event for platelet activation and aggregation to occur. These results therefore show that ADP-induced aggregation cannot be attributed to activation of P2Y1 alone, but must be attributed to the simultaneous activation of the high affinity receptor (P2Y1) and a low affinity receptor of ADP (still to be discovered), each of them essential, but neither able to trigger aggregation alone.
Savi et al. (Fri,) conducted a other in Platelet activation. A3P5PS (P2Y1 receptor antagonist) was evaluated on Platelet binding, shape change, calcium increase, and aggregation. A3P5PS, a P2Y1 receptor antagonist, displaced 27% of ADP analogue binding and inhibited platelet aggregation, demonstrating that P2Y1 activation is essential but not sufficient alone for aggregation.