Basic fibroblast growth factor increases junctional communication and connexin 43 expression in microvascular endothelial cells

We have analyzed the effect of basic fibroblast growth factor (bFGF) on junctional communication (coupling) and connexin 43 (Cx43) expression in bovine microvascular endothelial (BME) cells. In control confluent cultures, the incidence of coupling, as assessed by the intercellular transfer of microinjected Lucifer Yellow, was limited to 13% of injected cells, and decreased to 0% with time in culture. After exposure to bFGF (3ng/ml), the incidence of coupling was increased in a time-dependent manner, reaching a maximum of 38% of microinjected cells after 10-12 hours. The extent of coupling, as assessed by scrape loading, was maximally increased 2.1-fold 8-9 hours after addition of bFGF. bFGF also induced a 2-fold increase in Cx43 as assessed by Western blotting, and increased Cx43 immunolabelling at contacting interfaces of adjacent BME cells. Cx43 mRNA was likewise increased after exposure to bFGF in a time- and dose-dependent manner, with a maximal 6-7-fold increase after a 4 hour exposure to 3-10ng/ml. Finally, the increase in coupling and Cx43 mRNA expression observed after mechanically wounding a confluent monolayer of BME cells was markedly reduced by antibodies to bFGF, which have previously been shown to inhibit migration. Taken together, these results indicate that exogenous and endogenous bFGF increase intercellular communication and Cx43 expression in microvascular endothelial cells. We propose that the bFGF-mediated increase in coupling is necessary for the coordination of endothelial cells during angiogenesis and other vessel wall functions.