In vitro thrombus formation on surface-bound collagen. Blood was collected from anesthetized mice via a retro-orbital puncture using 40 U/mL heparin as anticoagulant. Apyrase was added to a final concentration of 1.5 U/mL. Glass coverslips were coated with insoluble fibrillar type I collagen (2.5 mg/mL) and placed in a parallel plate flow chamber. Mouse blood was treated with mepacrine for platelet visualization and perfused through the chamber at 1500/second wall shear rate. (A) Single frames taken from a continuous recording show the collagen-coated surface after 2.5 minutes of blood perfusion. In the left panel, thrombi formed by normal platelets are seen at a relatively low magnification (original magnification, × 10). The center and right panels show the surfaces exposed to GP VI^null and FcR-γ^null platelets, respectively, at a relatively higher magnification (original magnification, × 40); in either case, a complete surface coverage by single platelets is apparent, with formation of small clusters particularly in the case of FcR-γ^null platelets but absence of thrombus formation. See Video 1 for a clearer representation of these results. (B) Postperfusion thrombus volume was determined from serial z-sections. The results presented are the mean from 3 independent experiments.