CHINESE HAMSTER CELL MONOLAYER CULTURES .I. CHANGES IN CELL DYNAMICS AND MODIFICATIONS OF CELL CYCLE WITH PERIOD OF GROWTH

An investigation was carried out to contrast cellular kinetics of Chinese hamster cells in exponential and in plateau periods of growth, because of the possibility that cells in the plateau period may constitute a better model of tumor cell populations than do logarithmically growing cultures. The rates of synthesis (per cell) of RNA and protein were independent of cell number. On the other hand, the rate of DNA synthesis was closely coupled to the growth period of the culture. DNA synthesis (per cell) was constant during exponential growth but dropped to 10 per cent of its former value just before the cell number reached its maximum, indicating that a large proportion of the plateau period cells were in a G1-like part of the cell cycle. Those cells in the plateau period which continued to synthesize DNA went on to divide. The newly born cells replaced dead cells that had lysed. Thus the cell number remained stationary. The cell cycle of the reproducing cells in the plateau period was found to be characterized by an extended G2 and an extended and highly variable S phase. M did not appear to be changed greatly and G1 could not be measured. The similarities between the plateau period cell renewal system and populations of tumor cells are pointed out. © 1968.