Inhibition of MEK decreases Erk phosphorylation and VWF-mediated thromboxane production. Platelets were treated with the MEK inhibitor U0126 (10 μM) or its vehicle (control) before stimulation with VWF/ristocetin (8 and 300 μg/mL, respectively). Platelets were then processed for measurement of thromboxane production (A) or detection of phospho-Erk (B), as described in “Materials and methods.”