Activation of the Platelet Collagen Receptor Integrin α 2β 1: Its Mechanism and Participation in the Physiological Functions of Platelets

Abstract

When platelets are stimulated by agonists, integrin α 2β 1 (GP Ia/IIa), one of the platelet collagen receptors, is activated to forms with high affinities for its ligand collagen. Here we describe our studies to characterize the binding kinetics of the activated integrin forms and the activation mechanism. Under low agonist concentrations, integrin α 2β 1 is activated through a mechanism involving ADP/ADP receptors; and under high agonist concentrations, multiple signaling pathways are involved in its activation. Such differences in mechanism at low and high agonist concentrations are also suggested in the activation of integrin α IIbβ 3, the platelet fibrinogen receptor. We describe our flow adhesion studies, from which evidence was obtained about the involvement of integrin α 2β 1 activation in the physiological function of platelets, adhesion and thrombus formation.