Role of ADP Receptor P2Y12 in Platelet Adhesion and Thrombus Formation in Flowing Blood

ADP plays a central role in regulating platelet function. It induces platelet aggregation via the activation of 2 major ADP receptors, P2Y1 and P2Y12. We have investigated the role of P2Y12 in platelet adhesion and thrombus formation under physiological flow by using blood from a patient with a defect in the gene encoding P2Y12. Anticoagulated blood from the patient and from healthy volunteers was perfused over collagen-coated coverslips. The patient’s thrombi were smaller and consisted of spread platelets overlying platelets that were not spread, whereas control thrombi were large and densely packed. Identical platelet surface coverage, aggregate size, and morphology were found when a P2Y12 antagonist, N6-(2-methylthioethyl)-2-(3,3,3-trifluoropropylthio)-&bgr;,&ggr;-dichloromethylene ATP (also known as AR-C69931 MX), was added to control blood. The addition of a P2Y1 antagonist (adenosine-3′,5′-diphospate) to control blood resulted in small, but normally structured, thrombi. Thus, the ADP-P2Y12 interaction is essential for normal thrombus buildup on collagen. The patient’s blood also showed reduced platelet adhesion on fibrinogen, which was not due to changes in morphology. Comparable results were found by using control blood with AR-C69931 MX and also with adenosine-3′,5′-diphospate. This suggested that P2Y12 and P2Y1 were both involved in platelet adhesion on immobilized fibrinogen, thereby revealing it as ADP dependent. This was confirmed by complete inhibition on the addition of creatine phosphate/creatine phosphokinase.