F-actin increase and association of cofilin with F-actin during thrombin-induced secretion: effect of Y-27632. Platelets treated with H₂O (□) or Y-27632 (▪) were stimulated with thrombin (0.5 U/mL) in the presence of the integrin α_IIbβ₃ blocker RGDS (0.5 mM) and lysed with 1% Triton X-100 for isolation of F-actin. F-actin and cofilin associated with F-actin (percentage of total) were measured. (A) F-actin content, bar diagram. (B) Cofilin association with F-actin. (Top) Representative immunoblots. (Bottom) bar diagram (C) Bar diagram showing the ratio of F-actin–associated cofilin to F-actin. Values are the mean + SD for 4 independent experiments. *Statistically significant; P < .05 with respect to nonstimulated samples at 0 seconds. †Significance between control (□) and Y-27632 (▪)–treated platelets.