For the past year we continued to focus on the cell physiology of basic and acidic fibroblast growth factors, using both in vitro and in vivo models. Because these peptides have no signal sequences, the mechanism of their exit from the cell has been a mystery. We found in cultured endothelial cells that bFGF is localized to intracellular vesicles suggesting regulated (as supposed to continuous) secretion. Thus, cell death and other nonspecific forms of cell rupture are unlikely to be the only mechanism of exit from the cell. We also found that cultured adult rat cardiac myocytes, endothelial and smooth muscle cells have more acidic and basic FGF and FGF receptors than do the same cells in vivo. The cultured myocytes, endothelial and smooth muscle cells also revealed specific cytoplasmic and nuclear staining. Nuclear staining was confirmed by heparin affinity chromatography, mitogen assays, and Westerns. In cultured endothelial cells we found that migration in either low or high serum is associated with an increased expression of bFGF. Neutralizing antisera to bFGF caused some inhibition of migration of cells in low or high serum in the absence of added FGFs, suggesting that the FGFs are released by the migrating cells and that this facilitates their migration.
