Effect of vWF on shear-induced aggregation of washed platelets. Different shear rates were applied for 5 minutes at 20°C to washed platelet suspensions (1.5 × 108/mL) either in the absence of vWF (•) or in the presence of 10 μg/mL purified vWF (▪). After exposure to shear, samples were fixed with 1% paraformaldehyde. Forward and side light scatter dotplots were obtained by counting a constant volume in a flow cytometer. The single platelets region was determined in the buffer-containing unsheared sample and used as the reference value for calculation of disappearance of single platelets (DSP). Means ± SEM from three experiments performed in duplicate were expressed as a function of shear rate. In the absence of vWF, DSP of sheared platelets was hardly modified compared with the unsheared sample. In the vWF-containing samples, percent of DSP increased significantly with shear.
