Platelet aggregation is preserved in MYH9Δ mice despite absence of initial shape change. (A) Platelet aggregation in response to ADP, thrombin, collagen, and U46619 was barely impaired in MYH9Δ mice (numbers correspond to the concentration of agonist). The initial platelet contraction responsible for a transient decrease in light transmission (circled) was absent in MYH9Δ platelets. Tracings are representative of at least 3 experiments. (B) Shape change was evaluated in the aggregometer after stimulation of washed platelets with 5 μM ADP in the absence of fibrinogen and the presence of eptifibatid. Shape change was visualized by scanning electron microscopy and by the decrease in light transmission (inset), representative of 3 independent experiments (bars 2 μm).