Ca2+]i independent mitogenesis in cultured human fibroblasts revealed by single cell microfluorimetry

A transient rise in intracellular free Ca2+ concentration (Ca2+]i) has been implicated in mitogenic induction of cell division. Individual human foreskin fibroblasts in confluent cultures examined with the Ca2+ indicator Fura-2 and a fluorescence microscope-imaging system had a basal Ca2+]i which varied markedly from cell-to-cell. A transient serum-induced rise in Ca2+]i was demonstrated the magnitude of which was directly correlated with the basal Ca2+]i level. In contrast to serum-induced increase in Ca2+]i, exposure to an elevated level of extracellular Ca2+, which is at least equally mitogenic for fibroblasts, did not alter the basal Ca2+]i of single subconfluent cells or confluent cells. Elevated extracellular Ca2+ does not exert its mitogenicity via a transient rise in Ca2+]i.