Department of Molecular and Human Genetics, Baylor College of Medicine and Veterans Affairs Medical Center, Houston, TX 77030, USA

Tel: 713-794-7088, Fax: 713-794-7578

In the most reductionist view, platelet function can be considered as having three components: stickiness, excitability, and the ability to secrete bioactive substances. Platelets have several adhesive functions: they adhere to the blood vessel wall, to other platelets, and under certain conditions, to other blood cells. Platelets are also among the most excitable of cells, responding not only to chemical agonists but also to physical forces such as shear. Finally, platelets are packed with a potent arsenal of agonists and growth factors, which they may secrete at the slightest provocation. All of these functions impinge on what is the primary physiological role of platelets: the arrest of blood loss. In some way, each function also involves proteins on the platelet plasma membrane; some of these proteins are involved in carrying out several of these functions. The subject of this chapter, the glycoprotein (GP) Ib-IX-V complex, is one such protein. Although its primary function is in adhesion of the platelets to the vessel wall through its binding of subendothelial von Willebrand factor (vWf), this protein complex also plays a role in the response of the platelet to the most potent of its agonists, thrombin. Finally, through mechanisms of signal transduction that are far from clear, the complex is involved in signaling events that lead to platelet aggregation and secretion.