Flow-dependent characteristics of ₂β₁-mediated platelet attachment to pepsin-solubilized (nonbanded) type I collagen. Blood containing function blocking anti-_IIbβ₃ and anti-vWF A3 domain monoclonal antibodies (the latter to inhibit plasma vWF binding to collagen) was perfused over immobilized pepsin-solubilized (nonbanded) type I collagen in the parallel plate flow chamber as described in the legend to Fig 2. Note that, for stable platelet attachment under these conditions, there was an absolute requirement for ₂β₁-collagen interactions, because additional functional inhibition of ₂β₁completely inhibited platelet interaction with this substrate (as shown in Fig 6). The number of single platelets attached to the surface after 3 minutes of perfusion was measured as a function of the wall shear rate.