CalDAG-GEFI synergizes with P2Y12 signaling in Rap1 activation downstream of FcγRIIA. (A) Time course of Rap1 activation on stimulation of hFcR and hFcR/CDGI^−/− platelets with 10 μg/mL anti-CD9 in the absence or presence of 100μM 2-MeSAMP. (Bottom panel) Total Rap1 as loading control. (B) Densitometric analysis of Rap1-GTP shown as percentage of maximal activation (mean ± SEM, n = 3). (C) TxB₂ levels in the supernatant of hFcR and hFcR/CDGI^−/− platelets 4 minutes after stimulation with 5 μg/mL anti-CD9 in the absence or presence of 100μM 2-MeSAMP. Data are mean ± SEM (n = 6). *P < .05. ***P < .001. ns indicates not significant. (D) Aggregation response of hFcR/CDGI^−/− platelets activated with 1 μg/mL anti-CD9, 5μM U46619 (TxA₂ analog), or the combination of both agonists. Traces are representative of 4 independent experiments.