Strict relationship between dialyzed serum concentration and cellular life span in vitro.

To determine the extent of the contribution of growth factor level on the life span of human diploid fibroblasts in vitro, the growth rate changes of IMR-90 cells under altered dialyzed serum (d-FBS) concentrations were investigated at different population doubling levels (PDL). As the PDL increased, the cells showed an accelerated requirement for d-FBS in order to maintain a constant growth rate, thus indicating a rapid loss of responsiveness of the cells to serum growth factors. A similar relationship was observed when the growth rate was extrapolated to zero and the cellular life span was predicted from this relationship. The cells cultured with 0.3% and 10% d-FBS ceased their growth at 54 and 76 PDL, respectively, while their predicted life span was 58 and 80--85 PDL, respectively. The cells cultured with 0.3% d-FBS responded poorly to an increase in the d-FBS concentration after entering phase III. These results suggest that the serum growth factor level is one of the determinants of cellular life span in vitro.