Altered actin dynamics in Arpc2^fl/flPF4-Cre platelets. (A) Quantification of the surface area of unstimulated (resting) or stimulated platelets (500 μM Par4p, 750 ng/mL Cvx, or 10 μM adenosine 5′-diphosphate) spread on fibrinogen for 30 minutes (n = 5). (B) Representative immunofluorescent images of Cvx-stimulated platelets spread on a fibrinogen matrix and stained with phalloidin. (C) Representative scanning electron microscopy images of spread platelets on fibrinogen matrix from indicated mice, stimulated with Cvx (750 ng/mL). (D) Quantification of platelet F-actin (I), G-actin (II), and F-actin:G-actin ratio (III) at resting conditions or after stimulation with Par4p (500 μM) or Cvx (1 μg/mL) for 10 minutes before fixation (n = 5). (E) Representative transmission electron microscopy images of resting platelets from indicated mice; boxes indicate location of intracellular tubulin ring bundles. Scale bar, 200 nm. (B) Representative immunofluorescent images of tubulin rings in resting platelets from indicated mice. Blue bars, control; red bars, Arpc2^fl/flPF4-Cre. Data presented as mean ± SEM. *P < .05, **P < .01, ***P < .001.