P2Y receptors are members of a large family of G protein-coupled receptors that is classified into five functionally characterized human gene products (P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11). P2RY1 or P2Y1 is a GPCR that binds to ADP and ATP to activate Gq. P2Y1 express on vascular endothelium and smooth muscle, and mediate vascular tone both in the resting state and in thrombosis, when platelet-derived ATP and ADP are present at high concentrations. In addition, activation of P2Y1 expressed on platelets leads to ADP-induced shape changes and aggregation.