Spreading on collagen is impaired in VAMP-7^−/− platelets. (A) Fluorescence microscopy of wild-type and VAMP-7^−/− platelets spread for the indicated amounts of time on collagen and stained with Alexa 546 Phalloidin. Scale bars represent 5 μm. (B) Quantification of surface area (left) and perimeter of spread platelets (right) from wild-type (●) and VAMP-7^−/− mice (○) spread on collagen (**P < .01). Error bars represent the standard deviation of measurements from 79 to 384 platelets per time point. (C) Statistical analysis of platelet spreading was performed by quantification of the number of platelets at various stages of spreading as described by Pleines et al.⁵⁰  According to this method, a value of 1 (black) indicates rounded platelets that lack pseudopodia or lamellipodia; 2 (gray) indicates platelets with pseudopodia only; 3 (dark gray) indicates platelets with pseudopodia and lamellipodia; and 4 (light gray) indicates fully spread platelets with lamellipodia only. This analysis was performed at the indicated time points after seeding on collagen. V7 Null, VAMP-7^−/−; wt, wild-type.