Kinetics of SIPA and effect of increasing shear rates on platelet aggregation. (A) Washed platelets (2.8 × 10⁸/mL) were submitted to 0 s^–1 (open symbols) or 4000 s^–1 (closed symbols) for various times as indicated, in the presence of buffer (▵, ▴) or 2B-rVWF (□, ▪). (B) Platelets were submitted to a shear rate of 200 s^–1 or 4000 s^–1 for 4.5 minutes at 37°C in the absence (▴) or presence (▪) of 0.7 μg/mL 2B-rVWF. Following exposure to shear rates, an aliquot was fixed with 1.25% paraformaldehyde for 15 minutes. The results were expressed as the percentage of disappearance of single platelets (% DSP). Results are means ± SEM of 3 experiments.