Effect of VWF self-association on GPIbα binding. (A) Time course of GPIbα647 binding to Alexa Fluor 488–labeled tethered VWF in the presence of 20 nM GPIbα647 and 0, 10, or 50 μg mL⁻¹ of free unlabeled VWF at 960 dyn cm⁻² wall shear stress. Tension bins are keyed according to color. (B-C) Number of bound GPIbα647 molecules averaged over time periods between (B) 1.5 and 2.5 seconds and (C) 27 and 35 seconds after the start of flow at 960 dyn cm⁻². Data for 0, 10, and 50 μg mL⁻¹ of free VWF are averages over 48, 170, and 166 tethered VWF concatemers, respectively.