Exogenous TxA2 induces firm adhesion of CalDAG-GEFI−/− platelets to collagen. Whole blood from WT or CalDAG-GEFI−/− mice was perfused over a collagen surface at venous shear rates (400 seconds−1). (A) Representative images showing platelets firmly adherent to the collagen surface. U46619 (2 μM) was added to CalDAG-GEFI−/− (knockout [KO]) whole blood immediately before the perfusion. A total of 100 μM 2-MesAMP was added 10 minutes before the perfusion. Scale bar = 10 μm. (B) Quantification of adherent platelets. The data are presented as the mean ± SEM of the absolute number of platelets per 0.02 mm2 surface area. n = 9; 3 different blood preparations. **P < .01.