Actomyosin contraction compresses the coiled MB. (A) Platelets were diluted in PBS, 2.5 × 10⁶/ml, and pretreated with or without 25 or 50 µM blebbistatin (blebbi) or 1 µg/ml cytochalasin D for 30 min at RT. Platelets were then either activated with ADP (2.5-µM final) for 10 min at RT (bottom) or not activated (top), fixed, and stained for α-tubulin. Bars, 2 µm. (B) Putative sequence of events leading to platelet activation (to simplify, only two microtubules are shown in disc-shaped platelets).