The functional coupling of transplanted cells with host myocardial cells is a significant challenge in mesenchymal stem cell (MSC) cardiomyoplasty being related to cell survival and therapeutic outcomes. Priming of MSCs with growth factors has been reported to improve their therapeutic efficacy through gap junction-mediated mechanisms. However, the expression pattern of Connexin43 (Cx43) in growth factor-stimulated MSC was not previously addressed. In this study we investigated how the pretreatment with growth factors modulates MSC ability to integrate into the host tissue after transplantation, with particular focus on the expression of Cx43 and its cellular distribution. Our results showed that stimulation of MSCs with 1GF-1, FGF-2, but not TGF beta, increased the level of Cx43 at both mRNA and protein levels. IGF-1 stimulation resulted in a shift of the fibroblast morphology into an epithelial morphology in several well-defined areas of stimulated cells. Confocal microscopy examination revealed that the increase of Cx43 was restricted to the epithelial-like cells and did not occur in other cells. In variance, FGF-2 induced a rod-shape morphology of every single cell, which achieved an extremely low cell index. FGF-2 stimulation also induced a time-dependent increase in Cx43, with a regular distribution pattern in all cells. Dye transfer assay coupled with confocal microscopy and flow cytometry analysis demonstrated functional in vitro cell coupling between FGF-2-stimulated MSCs as well as between FGF-2-stimulated cells and H9c2 cardiomyoblasts, a scenery that mimick MSC transplantation into the myocardium. We conclude that the stimulation of MSCs with FGF-2 prior to transplantation may facilitate their access among the myocardial cells and increase the functional coupling between transplanted and host cells. (C) 2015 Elsevier Inc. All rights reserved.