Effect of valinomycin on collagen-plus-thrombin–induced procoagulant activity of platelets from a patient with Scott syndrome. Prothrombinase activities, expressed as nanomolar thrombin formed per minute, were determined after activation with collagen (10 μg/mL) plus thrombin (4 nM) in the absence (▪) and presence (▦) of valinomycin (3 μM). Data are mean values ± 1SD(n = 6).