Effects of colchicine and vinblastine on platelet contractility and release

Pre-incubation of normal platelet-rich plasma for 30 minutes at 37 degrees C with concentrations of colchicine (2.5 x 10(-4)M) or vinblastine (1.1 x 10(-4)M) which disrupt platelet microtubles did not inhibit aggregation induced by ADP or collagen. Even following pre-incubation of platelets with a 10-fold higher concentration of colchicine (2.5 x 10(-3)M), platelets released 14C-serotonin and aggregated in response to collagen. In the presence of a 10-fold higher vinblastine concentration (1.1 x 10(-3)M), platelets lysed and released 51Cr. Dynamic viscoelastic measurements on recalcified platelet-rich plasma in a Weissenberg rheogoniometer demonstrated that neither colchicine (2.5 x 10(-4)M to 5 x 10(-3)M) nor vinblastine (1.1 x 10(-4)M) interferes with the initiation, rate of generation, or extent of contractile force produced in platelet-fibrin clots. These results indicate that polymerized tubulin is not essential for collagen-induced release of platelet dense granule contents. In addition, intact tubulin polymers are not required to support the platelet surface configuration necessary for platelet-fibrin adherence and the platelet contractile events which result in platelet-fibrin clot retraction.