Platelet spreading on immobilized matrices is restrained by Shh antagonists. Phalloidin FITC-labeled platelets were pretreated with vehicle (control) cyclopamine (10 μM) or vismodegib (25 μM) as indicated. (A) Platelets treated with thrombin (0.5 U/mL) were allowed to spread over an immobilized fibrinogen matrix for 15 minutes. Images are representative of 5 different fields, each from 3 independent experiments. (B) Thrombin (0.5 U/mL)-treated platelets were allowed to spread over immobilized collagen matrix for 15 minutes. Images are representative of 10 different fields, each from 3 independent experiments. (C-D) Corresponding quantification of platelet spreading on fibrinogen and collagen matrices, respectively. Figures are representative of ≥3 individual experiments (mean ± standard error of the mean). *P < .05 as compared with vehicle-treated control platelets.