Mechanisms-regulated platelet spreading after initial platelet contact with collagen.

In static condition, 6F1, an anti-glycoprotein Ia/IIa monoclonal antibody, almost completely prevented initial platelet adhesion to fibrillar collagen, but markedly lost its action with prolonged incubation. The platelet adhesion and spreading at the later stage were prevented by adding the peptide GRGDS, aspirin, and apyrase, suggesting that after initial recognition of platelet glycoprotein Ia/IIa with collagen the activation of glycoprotein IIb/IIIa and the release of thromboxane A2/ADP would promote platelet spreading, thus strengthening the stability of adhesion. Both initial platelet adhesion and platelet spreading were prevented by cytochalasin B, an inhibitor of actin polymerization. In contrast, BAPTA (an intracellular Ca2+ chelator) only inhibited platelet spreading. Inhibition of protein kinase C or protein tyrosine kinase by staurosporine or genistein, respectively, had only little effect on platelet adhesion. These data suggest that actin polymerization and intracellular Ca2+ mobilization are involved in the regulation of platelet spreading after initial platelet contact with collagen.