EphrinB1 signaling potentiates Rap1 activation. (A) Gel-filtered platelets were incubated with the agents indicated, then Rap1-GTP was isolated and analyzed as described in “Materials and methods.” (B) Washed platelets (500 × 10⁹/L) were preincubated for 15 minutes with apyrase 1 U/mL, LY294002 100 μM, PP2 30 μM, or vehicle, then stimulated with agonist for 5 minutes. The results are from 1 of 2 experiments with identical results.