Molecular physiology of platelet ADP receptors

Extracellular nucleotides have been implicated in a number of physiologic functions. Nucleotides act on cell surface receptors known as P2 receptors of which several subtypes have been cloned. Both ATP and ADP are stored in platelets and are released upon platelet activation. During vascular injury, nucleotides play an important role in hemostasis by activating platelets. Classic pharmacologic studies have identified ADP receptors on platelets, designated P2T receptor. The P2T receptor is now resolved into three P2 receptor subtypes, the P2Y1, the P2X1, and the P2TACreceptor, which remains to be cloned. Although the P2Y1 receptor solely mediates ADP-induced platelet shape change, both the P2Y1 and P2TAC receptors are essential for ADP-induced fibrinogen receptor activation on platelets. The function of the P2X1 receptor remains to be elucidated. Thus the complexities in the functional characterization of platelet ADP receptors now appear to be resolved. Drug Dev. Res. 45:135–139, 1998.