vWF-dependent heparin-induced CHO-GPIbβ/IX cell aggregation. CHO-GPIbβ/IX cell aggregation was performed in the presence (▪) or in the absence (□) of 10 nmol/L vWF by adding varying concentrations of heparin (0 to 250 μg/mL) at a rotary shaking of 6 cycles per second. The mean ± SEM of 4 separate experiments is shown. Heparin-induced dose-dependent CHO-GPIbβ/IX cell aggregation in the presence of vWF.