The endothelial barrier is essential for vascular function, and its disruption may play a major role in development of cardiovascular diseases. An increase in cAMP level tightens the endothelial barrier by enhancing junction formation, and this is, in part, mediated by activation of exchange protein directly activated by cAMP (Epac) (Fukuhara et al. 2005). We have investigated the effect of Epac activation on two key junctional proteins, VE-cadherin, which forms adherens junctions, and Cx37, which forms gap junctions. Human coronary artery endothelial cells (HCAECs, Promocell) were cultured to ~90 % confluence, and Epac was activated by application of 5 μM 8-pCPT-2′-O-Me-cAMP AM (8-pCPT AM), a specific Epac agonist. The effect of 8-pCPT AM was studied on: (i) The distribution of VE-cadherin and Cx37 by immunocytochemistry using confocal microscopy, and, (ii) The diffusion of Lucifer yellow using a scrape assay.Staining of VE-cadherin showed short, broken lines around the periphery of control HCAECs while that of Cx37 appeared as patchy plaques. Treatment with 8-pCPT AM for 30 minutes caused VE-cadherin staining to re-locate toward the edge of HCAECs and form continuous lines between adjacent cells. Co-localization of VE-cadherin and Cx37 was examined using image J. Means and SEM of Mander’s overlap coefficients were determined for control (n=6) and 8-pCPT AM- treated HCAECs (n=5) with significant difference (0.233 ± 0.039 and 0.358 ± 0.022, P< 0.05, unpaired t-Test).Scrape assays were carried out for control cells, cells treated with 8-pCPT AM for 30 minutes, and cells treated with 8-pCPT AM in the presence of Epac antagonists HJC0192 (5 nM) or ESI-09 (5 nM). The distance Lucifer yellow diffused from the wound edge after 2 minutes was 158.7 ± 17.50, 269.5 ± 28.53, 167.7 ± 15.23 and 218.0 ± 20.82 μm, respectively (mean ± SEM n=12). Statistical analysis using ANOVA showed significant difference between control and 8-pCPT AM treated HCAECs (p<0.01). Significant difference was also detected between HCAECs treated with 8-pCPT AM alone and cells treated with 8-pCPT AM in the presence of HJC0192 (p<0.01). These results suggest that intercellular communication between HCAECs was enhanced by Epac activation, and this effect was blocked by an Epac antagonist. Our results are consistent with the hypothesis that activation of Epac enhances intercellular communication by modulating adherens junctions and gap junctions in HCAECs. The effect of Epac occurs as re-distribution of VE-cadherin and Cx37. Functionally, activation of Epac leads to the facilitation of intercellular communication between HCAECs. Epac may play an important role in regulation of endothelial barrier function in response to agents that elevate cAMP.