The regulation of intracellular calcium ion and pH in young and old fibroblast cells (WI-38).

The cytosolic free calcium concentration ([Ca2+]i) and the cytoplasmic pH (pHi) in young and old cells of normal human diploid cell line, WI-38, were measured with the fluorescent probes, fura-2 and BCECF, respectively. The basal concentrations of cytosolic calcium in young and old cells were approximately the same (40-50 nM). In order to investigate the difference in the regulation of calcium mobilization between young and old cells, both cell lines were stimulated with bradykinin (BK, 0.5 microM), and [Ca2+]i was monitored by fluorescent imaging. The [Ca2+]i increased within 10 sec following bradykinin exposure. The peak values for young and old cells were about 10 and 8 times higher than the basal level. After the peak, the recovery rate in young cells was slower than in old cells. This difference between young and old cells may be due to the change of the influx of extracellular calcium, as this difference was not observed in the calcium free medium. These data suggest that calcium influx may be reduced during cell aging. Intracellular pH in old cells was found to be more acidic than that of young cells in media with either 0.1% or 10% serum. This finding indicates that cell aging might induce acidification which in turn causes an inhibition of cell growth. The relationship between acidification and the activity of calcium channel in old cells is also discussed.