Increased platelet accumulation at the site of vascular injury in GRK2^−/− mice. (Ai) Representative images of hemostatic plugs formed in WT and GRK2^−/− mice 1.5 minutes after injury. (Aii) Confocal intravital fluorescence microscopy was performed to follow platelet accumulation (CD41) and P-selectin expression over 3 minutes. (Aiii) Platelet accumulation at the site of injury as measured by CD41 (area under the curve [AUC]) for 61 injuries in 7 WT mice and 41 injuries in 7 GRK2^−/− mice. (Aiv) P-selectin positivity expressed as AUC. Forty-three injuries in 7 WT mice and 35 injuries in 7 GRK2^−/− mice. (Bi) Fibrin deposition was examined after making small penetrating injuries in the cremaster muscle arterioles with a laser in GRK2^−/− mice and littermate control mice. Thirty injuries in 7 WT mice and 29 injuries in 7 GRK2^−/− mice. (Bii) Fibrin accumulation as measured by the mean fibrin area at the end of the 3-minute interval. Data sets were compared by using a two-by-two unbalanced analysis of variance. Data are presented as mean ± standard error of the mean.