ABSTRACT

The main adhesion mechanism binding the platelet to the subendothelial matrix is via collagen. There are two main collagen receptors on the platelet membrane, GPIa/IIa and GPVI. GPIa/IIa serves as an anchor for platelets to connect to exposed collagen, 2 while GPVI activates adhesive receptors, including GPIa/IIa, which strengthen collagenplatelet adherence. 3 Collagen, while serving as the scaffolding for platelet adherence, also activates platelets by intracellular second messengers. 4 Other molecules that activate platelets include epinephrine (adrenaline), serotonin, and adenosine diphosphate (ADP), as well as vWF. 5

One of the most potent activators of the platelet is thrombin. The primary thrombin receptor on the platelet is protease-activated receptor 1 (PAR-1). Thrombin, thromboxane A 2 (TXA 2 ), and ADP directly activate the platelet through G-protein-coupled receptors, leading to platelet aggregation and granule release. 6 The ADP receptors on the platelet are P2Y 1 and P2Y 12 .