Hyperthermia and thermal tolerance in normal and ataxia telangiectasia human cell strains

Three normal human fibroblast strains, two human ataxia telangiectasia heterozygote cell strains, and two human ataxia telangiectasia homozygote cell strains were studied for their thermal responses between 41.0 and 46.0 degrees. The heat sensitivities of all cell strains were comparable, and all cell strains were relatively heat resistant compared to Chinese hamster cells. Both normal and ataxia telangiectasia human cells developed thermal tolerance during heating at temperatures less than or equal to 43 degrees and during incubation at 37 degrees after acute heating at 45.0 degrees. For survival measured down to the 5 to 10% level, heat survival curves for all seven human cell strains lacked shoulders, indicating the inability of such cells to accumulate sublethal heat damage. Analysis of the cell survival curve data by the method of Arrhenius showed that the thermal inactivation energies for human cells were 127 and 230 kcal/mol above and below the break at 43.5 degrees, respectively, and are about the same as for Chinese hamster cells and other animal cells, implying similar mechanisms of heat inactivation.