Microtubule coils in spread blood platelets.

The fate of the circumferential bundle of microtubules in activated platelets has been a subject of disagreement. Thin sections of stimulated platelets fixed at multiple intervals following exposure to aggregating agents have revealed that the circumferential band is constricted into a tight ring around centrally concentrated organelles. However, studies of detergent-resistant platelet cytoskeletons fixed and either negatively stained or critical point dried after activation on polylysine-coated grids have revealed that microtubule rings disappear, leaving only fragments in the peripheral cytoplasm of spread cells. The present study has employed immunofluorescence on glass slides and the whole mount technique with detergent extraction and either negative staining or critical point drying to evaluate the fate of microtubules in surface-activated platelets treated with or without the microtubule stabilizing agent, taxol. Significant numbers of microtubule coils were visible in control and taxol-treated platelets stained indirectly with a fluorescein-coupled antibody to tubulin 30 to 60 minutes after surface activation on glass. Coils of microtubules were also visible in dendritic forms and in significant numbers of spread platelets on negatively stained or critical point dried whole mounts in the electron microscope. The findings support the concept that microtubule disassembly is not an integral step in early phases of platelet activation.