Platelet adhesion, cohesion, and [Ca²⁺]i elevation on a vWF-coated surface under varying shear rates. Reconstituted blood containing platelets loaded with the Ca²⁺ indicators Fura Red and Calcium Green-1 was perfused over a vWF-coated surface with various shear rates. (Upper panels) Images obtained at 8 minutes of perfusion at a shear rate of 50 s⁻¹, 750 s⁻¹, or 1,500 s⁻¹, representative of 5 independent perfusions using blood from 5 donors. Note greenish cohered platelets (high [Ca²⁺]i) at 1,500 s⁻¹, but red, sparsely adhered platelets (low [Ca²⁺]i) at 50 s⁻¹. Images represent an area of 2,380 μm² in a single frame with an original magnification of 1,000×. (Lower panels) Extent of platelet [Ca²⁺]i elevation and platelet adhesion/cohesion at various shear rates (50, 250, 500, 750, 1,500, and 3,000 s⁻¹) evaluated as the signal ratio of green/red channels (G/R ratio) and the percentage of surface area covered by adhering and cohering platelets. Images obtained at 8 minutes of perfusion at the various shear rates were analyzed. Data represent the mean and standard deviation (SD) of results from 5 areas (4,760 μm² each) randomly selected from images derived from 5 independent perfusions. Note that the G/R ratio (preperfusion value, 0.82 ± 0.06) and surface coverage of platelets increased as a function of shear rate, reaching a plateau at 1,500 s⁻¹ (P < .01; evaluated by one-way repeated measures ANOVA with assist of Stat View computer software; Abacus Concepts Co, Berkeley, CA).