Video microscopy of platlet attachment to human type I collagen at high shear (1,500/s). Real-time epifluorescence video microscopy showing the time courses of platelet adhesion in whole blood to surface-bound solubilized human type I collagen at 1,500/s. Single-frame images obtained during a typical comparison are depicted. These data, derived from one donor pairwise analysis, are representative of results obtained from six donors. Upper row: normal donor, homozygous allele 1 (807T) genotype, High platelet α₂β₁ density; bottom row: normal donor, homozygous allele 2 (807C) genotype, Low platelet α₂β₁ density. Time after initiation of whole blood flow is shown above each column. Platelet α₂β₁ density was determined by flow cytometry and is expressed as a normalized mean fluorescence intensity (nMFI).9 The range of nMFI for 32 normal subjects is 1.0 to 9.4. In the experiment depicted here, the nMFI values for each donor are: High, 9.2; Low, 2.2.