Activation of ephrinB1 or EphA4 causes platelet adhesion to fibrinogen. Adhesion was measured using a colorimetric assay as described in “Materials and methods.” (A) Platelets were incubated with ADP (20 μM) or without an agonist for the times indicated. The figure is representative of 3 experiments. (B-C) Platelets were stimulated with ADP (20 μM), GST-EphB1 (5 μg/mL; panel B), or GST-ephrinA4 (5 μg/mL; panel C) for the times indicated. The results are the mean ± SEM for 4 experiments expressed as the “adhesion index,” which is defined in “Materials and methods.”