SOME CHARACTERISTICS OF HYPEROXIA-ADAPTED HELA-CELLS - A TISSUE-CULTURE MODEL FOR CELLULAR OXYGEN TOLERANCE

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 52  (4) , 420-428
Abstract
By culturing HeLa cells at stepwise increased O2 tensions over a prolonged period of time (.apprx. 21 mo.) a substrain capable of growing under 80% O2/19% N2/1% CO2, an O2 level that is lethal to normal HeLa cells, adapted to 20% O2/79% N2/1% CO2 were selected. The 80% O2-adapted cells exhibited the following characteristics. At the ultrastructural level an abnormal mitochondrial morphology was observed: compared to normal cells, mitochondria of the hyperoxia-adapted cells exhibited a 3-fold larger mean profile area in sections and were slightly decreased in number; the relative mitochondrial volume was increased 2-fold, whereas the size of both cell types was the same. Mitochondrial matrix appeared less dense in the hyperoxia-adapted cells; no structural damage was detected. Compared to the 20% O2-adapted cells O2 consumption per cell was .apprx. 40% decreased in the 80% O2-adapted cells. Under hyperoxic conditions 20% O2-adapted and 80% O2-adapted cells exhibited very similar cyanide-resistant respiration rates (0.16 .+-. 0.04 and 0.15 .+-. 0.02 fmoles/cell per min, respectively), suggesting that the increased O2 tolerance of the 80% O2-adapted cells was not due to a decreased cellular production of activated O2 species at hyperoxia. Cellular levels of the enzymes directly involved in protection against activated O2 species, i.e., superoxide dismutases, catalase and glutathione peroxidase, were normal or slightly below normal in the 80% O2-adapted cells, implying that these enzymes were of no significance for the increased O2 tolerance. In addition, the specific activity of glucose-6-phosphate dehydrogenase, a key enzyme for cellular production of NADPH, was not related to the degree of O2 tolerance. The increased O2 tolerance of the 80% O2-adapted cells apparently is neither based on cellular properties controlling the formation or removal of intracellular activated O2 species nor on the cellular capacity to repair or replace damaged cellular components. The increased O2 tolerance evidently is largely due to a genetically determined increased resistance of O2-sensitive cellular targets.