The association of pp125FAK, pp60Src, CDC42Hs and Rap1B with the cytoskeleton of aggregated platelets is a reversible process regulated by calcium.

The integrin alpha IIb beta 3-mediated redistribution of the tyrosine kinases pp125FAK and pp60Src 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 pp125FAK, pp60Src, 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.