The association of pp125^FAK, pp60^Src, CDC42Hs and Rap1B with the cytoskeleton of aggregated platelets is a reversible process regulated by calcium

Abstract

The integrin α_IIbβ₃-mediated redistribution of the tyrosine kinases pp125^FAK and pp60^Src and the small GTP-binding proteins CDC42Hs and Rap1B from the membrane skeleton to the cytoskeleton was found to be reversible: upon prolonged platelet aggregation (up to 15 min) induced by the thrombin-receptor activating peptide (TRAP) these signalling proteins dissociated from the cytoskeleton and reappeared in the membrane skeleton. Addition of the extracellular Ca²⁺ chelator EGTA and the intracellular Ca²⁺ chelator BAPTA/AM 30 s after TRAP allowed platelet aggregation and the association of pp125^FAK, pp60^Src, CDC42Hs and Rap1B with the cytoskeleton, but prevented their dissociation from the cytoskeleton. The results indicate that the prolonged elevation of cytosolic Ca²⁺ in stimulated platelets leads to the dissociation of signalling proteins from the cytoskeleton.