CHANGES IN CELL PROLIFERATION KINETICS OCCURRING DURING THE LIFE HISTORY OF MONOLAYER CULTURES OF A MOUSE TUMOUR CELL LINE

Following inoculation of monolayer cultures of EMT6 mouse tumour cells at 10⁵ cells, a short lag is followed by 3 days of exponential growth with a population doubling time of 12 hr. A plateau cell number is reached between days 4 and 5 and is maintained for at least 8 days. During exponential growth, the pulse ³H-TdR labelling index is 55–60%, all cells are in cycle, and the median cycle time is 11–12 hr. For the first 3 days of plateau phase, the labelling index is about 25 % and there is considerable cell loss. The cell cycle is 32–40 hr, and S-phase is very long. Later in plateau phase, the labelling index falls to <2 % and there is little cell loss. The changes in kinetics occurring in EMT6 cultures are discussed with reference to reported changes occurring in other cell lines.