Effect of VCL on vWF-dependent ristocetin- or heparin-induced CHO-GPIbβ/IX cell aggregation. After preincubation of CHO-GPIbβ/IX cells with increasing concentrations of VCL, cell aggregation was performed at 6 cycles per second in the presence of 1.4 mg/mL ristocetin (□, ▪) or in the presence of 50 μg/mL heparin (•, ○). Solid symbols are samples incubated in the presence of 10 nmol/L vWF; open symbols are samples incubated without vWF. The mean ± SEM was obtained from 3 experiments. The VCL fragment competed with vWF for binding to GPIb.