Platelet adhesion and NO and calcium elevation on immobilized fibrillar type I collagen: role of different integrins and GPIbα. DAF-FM- or FLUO 3-AM–loaded platelets, prepared as described in the legend to Figure 2, were perfused over immobilized fibrillar collagen type I at a shear rate of 3000 s⁻¹ for 3 minutes. When indicated, blood cells were incubated for 10 minutes at 37°C with 100 µg/mL of LJ-CP8, a monoclonal anti-α_IIbβ₃ antibody that completely blocks fibrinogen and von Willebrand factor binding, or 100 µg/mL of LT-1bI, an anti-GPIbα monoclonal antibody, or 100 µg/mL of an anti-α₂β₁ monoclonal antibody specific for the α₂ integrin.³²  Platelets present in each optical field (control: 40-60/field) were enumerated and expressed as percentage of the control (A). The number of FLUO 3-AM–loaded platelets in which at least one [Ca⁺⁺] elevation was observed, was enumerated over a 3-minute period as a fraction of the percentage of adhering platelets, in the absence (control) or presence of different antibodies, as indicated (B). At the same time, the DAF-FM–loaded platelets exhibiting a fluorescence increase over a 3-minute period were enumerated as a fraction of the percentage of adhering platelets in the absence (control) or in the presence of different antibodies, as indicated (C). Data are the mean ± 95% CIs of at least 3 different experiments. Significant difference from the corresponding control: *P < .05, **P < .01, ***P < .001.