Time course of platelet adhesion on type I collagens with distinct structural specificities at a wall shear rate of 1,500 s⁻¹. (A) Control blood (containing no antibody) or blood treated with a function blocking anti-₂β₁monoclonal antibody was perfused through a parallel plate chamber as described in the legend to Fig 2, and the flow rate was adjusted to produce a wall shear rate of 1,500 s⁻¹ at the inlet of the chamber. Single frame images corresponding to an area of 65,536 μm² were captured from videotapes at various times after the onset of blood flow and analyzed for the area occupied by surface covered platelets (indicated as surface coverage). Note the differential effects of inhibiting platelet ₂β₁ function with type I collagens having distinct structural features, particularly the differences seen between reconstituted collagen and pepsin-solubilized collagen (nonbanded) from which it was derived. Surface coverage measurements represent the mean ± standard error of the mean of 4 separate experiments with different blood donors. (B) Blood containing an anti-₂β₁ monoclonal antibody, either alone or concurrently with an anti-_IIbβ₃monoclonal antibody, was perfused over reconstituted type I collagen at a wall shear rate of 1,500 s⁻¹. After 3 minutes of perfusion (corresponding to time 0), consecutive images were captured from videotapes and analyzed for platelet movement (for definition, see Materials and Methods). The percentage of platelets displaced from their initial position was calculated as a function of time relative to the total number of platelets attached to the surface in the first image analyzed. Note that approximately 80% of all platelets (indicated as platelets displaced) moved on the surface within 3 seconds of observation when ₂β₁ and _IIbβ₃ were inhibited concurrently, compared with greater than 60% of the platelets remaining stationary after selective inhibition of _IIbβ₃. The 2 single frame images on the right, each representing an area of 65,536 μm², depict surface coverage after 3 minutes of perfusion with selective _IIbβ₃ inhibition (lower) or combined _IIbβ₃ and ₂β₁ inhibition (upper). Note the differences in surface coverage by platelets, reflecting differences in the stability of platelet attachment.