Platelet cytoskeletal components involved in shape change and secretion.

We investigated the role of cytoskeletal components in platelet activation under conditions in which changes in the shape of platelets, their secreting reaction, or both, would occur. When rabbit platelets were stimulated with 0.1 U/ml thrombin, they changed their shape, secreted serotonin, and incorporated actin-binding protein (ABP), myosin, and actin into their cytoskeletons. Platelets treated with 2 microM cytochalasin E and stimulated with 0.1 U/ml thrombin secreted serotonin and assembled myosin and actin into their cytoskeletons, but did not change in shape. Stimulation with a low dose of thrombin (0.001 U/ml) or ADP (10 microM) caused a change in shape and incorporation of ABP, myosin, and actin, but not serotonin secretion. These results suggest that the assembly of myosin and actin into platelet cytoskeletons is related to the secreting reaction, and that ABP, myosin, and actin are all involved in the changes in platelet shape.