Cdc42^−/− platelets form larger aggregates on collagen under flow. Whole blood from wild-type or Cdc42^−/− mice was perfused over a collagen-coated surface (0.2 mg/mL) at a shear rate of 1000 seconds⁻¹. (A) Top row: representative phase contrast and fluorescence images of aggregate formation on collagen after 4 minutes of perfusion time. Scale bar equals 100 μm. Bottom row: mean surface coverage (left) and relative thrombus volume expressed as integrated fluorescence intensity (IFI) per square millimeter (right) ± SD of 6 mice per group. Left: wt, 57.58 ± 6.40; Cdc42^−/−, 47.72 ± 1.13 [%]; P = .112. Right: wt, 3.80 ± 0.54; Cdc42^−/−, 4.95 ± 0.20 [IFI/mm²]; *P = .037. (B) Decreased life span of Cdc42^−/− platelets. Determination of the percentage of fluorescently labeled platelets of wild-type (■) and Cdc42^−/− platelets (▩) for 5 days upon injection with 0.5 μg/g bodyweight GPIX-Dylight 488 derivate on day 0. ***P < .001. (C) Increased tail bleeding times in Cdc42^−/− mice () compared with wild-type (●) mice. Each symbol represents 1 animal.