The platelet membrane: some aspects of the pathophysiology of haemostasis.

Platelet membranes play a key role in all stages of the haemostatic mechanism. Four of these in particular are considered here: adhesion to subendothelium, which involves an interaction between the glycoprotein I complex in the platelet membrane (deficient in the Bernard-Soulier syndrome) and plasma factor VIII; aggregation, involving the membrane glycoprotein IIb/IIIa complex (deficient in thrombasthenia), plasma fibrinogen and divalent cations; platelet factor 3 availability, a function of surface membrane phospholipids; and thromboxane synthesis, a function of the phospholipids of the membrane of the dense tubular system. The glycoprotein I complex also carries binding sites for thrombin and for drug-dependent antibodies, and glycoprotein IIb/IIIa is the site of the P1A1 antigen and of alpha-actinin.