HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY P2Y1 and P2Y12 receptors for ADP desensitize by distinct kinase-dependent mechanisms

Adenosine 5 -diphosphate (ADP) plays a central role in regulating platelet function by the activation of the G protein–coupled receptors P2Y1 and P2Y12. Although it is well established that aggregation responses of platelets to ADP desensitize, the underlying mechanisms involved remain unclear. In this study we demonstrate that P2Y1and P2Y12-mediated platelet responses desensitize rapidly. Furthermore, we have established that these receptors desensitize by different kinase-dependent mechanisms. G protein–coupled receptor kinase (GRK) 2 and GRK6 are both endogenously expressed in platelets. Transient overexpression of dominant-negative mutants of these kinases or reductions in endogenous GRK expression by the use of specific siRNAs in 1321N1 cells showed that P2Y12, but not P2Y1, desensitization is mediated by GRKs. In contrast, desensitization of P2Y1, but not P2Y12, is largely dependent on protein kinase C activity. This study is the first to show that both P2Y1 and P2Y12 desensitize in human platelets, and it reveals ways in which their sensitivity to ADP may be differentially and independently altered. (Blood. 2005;105:3552-3560)