Inhibition of Src kinases or phospholipase C blocks VWF-mediated platelet aggregation. Platelets were treated with the Src kinase inhibitor PP2 (10 μM), its inactive analog PP3 (10 μM), or the PLC inhibitor U73122 (10 μM) before stimulation with ristocetin (300 μg/mL) and VWF (8 μg/mL). Platelet aggregation was measured as described in “Materials and methods.”