Expression of Epac1 in EPCs. (A) Expression of Epac1 in HUVECs and EPCs as assessed by Western blot. (B) Human EPCs were stimulated for 5, 15, and 30 minutes in suspension with 8-pCPT-2′-O-Me-cAMP 100 μM. The level of GTP-bound (active) Rap1 was assessed. A representative blot from 3 independent experiments is shown. (C) Densitometric analysis of Rap1 activation in EPC from 3 independent experiments. Error bars represent SEM.