Immunogold staining of microtubules in resting and activated platelets.

A circumferential microtubule is known to support the discoid form of resting platelets, but its fate following exposure of the cells to aggregating agents is uncertain. The present study has employed an immunocytochemical approach to follow the fate of the circumferential microtubule in activated platelets. Monoclonal antibodies to tubulin and to vinculin and a polyclonal antibody to actin were incubated with isolated microtubule coils and stained with staphylococcal protein A coupled to immunogold in order to test their specificity. Thin sections of glycolmethacrylate embedded platelets before and after exposure to thrombin for 15, 30 and 60 s were stained with antibodies to tubulin and actin. Immunogold particles showed a high specificity for isolated MT coils stained for tubulin, modest intensity for actin, and none for vinculin. Gold particles were randomly distributed in thin sections of resting and activated platelets stained for actin. Immunogold was limited to the circumferential microtubule in resting platelets and constricted coils in thrombin-activated cells. The number of gold particles in areas of cytoplasm away from microtubules in platelets stained with antitubulin antibody increased slightly following thrombin activation, but the change was not significant. Results support the concept that microtubule coils supporting the discoid form of resting platelets do not dissolve following exposure of the cells to potent agonists.