Normal adhesion of β1-tubulin^—/—platelets under physiologic shear conditions. (A) Arterial thrombosis model. Wild-type or β1-tubulin^—/— mice were injected with fluorescently labeled platelets of matching genotype, and their mesenteries were exposed. When indicated, β1-tubulin–null mice were transfused with 0.5 × 10⁹ wild-type or β1-tubulin–null platelets 18 hours prior to the start of the experiment. Arterioles (60-100 μm in diameter) were selected, vascular injury was provoked by superfusion with ferric chloride, and the time before blood flow ceased for more than 10 seconds was determined. Each bar represents an individual animal. (B-C) Parallel-plate flow chamber studies. Platelets from mice of the indicated genotype were prepared as described in “Materials and methods” and then perfused for 2 minutes over a collagen surface at a wall shear rate of 1000 seconds^—1. (B) Surface-area coverage (%) of calcein fluorescence at different time points (20 seconds to 2 minutes) over the perfusion period; n = 5 independent animals of each genotype, and the statistical significance of observed differences between the 2 groups is indicated over each pair of bars. (C) Representative fluorescence images of a portion of the flow chamber for platelets derived from single mice.