Cell density-dependent regulation of ATP levels during the growth cycle of cultured Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells show a cell density-dependent modification of ATP levels during the growth cycle. Cells were seeded at a density of 500,000 cells/75 cm2 flask in 10 ml of growth medium and at various time intervals, samples were taken and assayed for cell number, for adenine (ATP, ADP, AMP) and pyridine (NAD+, NADP+) nucleotide levels and for the activity of some glycolytic enzymes. Glucose consumption was also evaluated. Experimental results indicated that the rate of cell growth was exponential for up to the 4th day of culture after which the cell number remained pratically unchanged up to the 9th day. Under these experimental conditions we found that, whereas the intracellular levels of NAD+ and some glycolytic enzymes were not significantly affected, a drop in ATP content was apparent after 48 hr of culture. The decline in ATP levels progressively increased, reaching a maximum after 4 days of culture, and then remained unchanged. In order to evaluate whether this effect on ATP was determined by a reduced availability of nutritional factors or was really a function of cell density, we also performed experiments similar to those reported above, with the exception that the cells were grown in 40 ml of culture medium. Under these experimental conditions, the exponential growth was longer (in comparison with the cell growth in 10 ml of medium) and a plateau was reached after 6 days of culture.(ABSTRACT TRUNCATED AT 250 WORDS)