The effect of 1 microM
antimycin on the proliferative properties, metabolism and basic cell composition of Ehrlich
ascites tumour cells cultured in the second in vitro passage was studied. Continuous
drug exposure of asynchronous cells caused rapid cessation of cell growth, characterized by the cell number and
DNA,
RNA and
protein content of cultures. Cells cease to consume
oxygen and enhance their glycolytic activity. Uptake of labelled
thymidine into
acid-insoluble material was far below that of the controls, whereas incorporation of labelled
uridine exceeded that of controls, as was also observed with other inhibitors of the respiratory chain (
sodium cyanide, 2-
thenoyltrifluoroacetone, or anaerobiosis). The influence of
antimycin on cells at different stages of the cell cycle was tested using cells enriched in either G1, S or G2 phase by centrifugal elutriation.
DNA histograms (flow cytometry) and pulse-labelling index curves gave detailed insight into cell-cycle progression of
antimycin-treated cells: G1 and early S cells remained stationary; G2 cells still passed from G2 into mitosis to remain subsequently in a non-growing state in G1; S cells were either slowed or halted. Supplementation of
antimycin-containing cultures with exogenous
pyrimidine nucleosides stimulated reprogression of G1 cells without changing their
ATP content. The results of the current experiments are interpreted as supporting the concept that growth cessation of G1 cells under
respiratory insufficiency is not predominantly caused by impairment of respiratory phosphorylation but may be the consequence of a lack of precursors for
DNA and
RNA synthesis.