Effect of heparin and ristocetin on vWF-dependent CHO-GPIbβ/IX cell aggregation. After incubation of CHO-GPIbβ/IX cells with increasing concentrations of heparin or ristocetin, cell aggregation was performed at 6 cycles per second in the presence of 10 nmol/L vWF and was induced by 1.4 mg/mL ristocetin (A) or 50 μg/mL heparin (B). The mean ± SEM was performed on 4 separate experiments. Heparin inhibited the ristocetin-induced CHO-GPIbβ/IX cell aggregation and ristocetin inhibited the heparin-induced CHO-GPIbβ/IX cell aggregation.