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Intrinsic Differences in Heat and/or X-Ray Sensitivity of Seven Mammalian Cell Lines Cultured and Treated under Identical Conditions¹

Department of Radiology and Radiation Biology, Colorado State University, Fort Collins, Colorado 80523

The variation in heat and/or X-ray response of 7 mammalian cell lines treated under identical culture conditions and experimental procedures was examined. Large differences in thermal response at 42.5 and 45.5° (dose-modifying factors of greater than 10) were observed among the cell lines, and the order of heat sensitivity for the 7 cell lines was similar but not identical at 42.5 and 45.5°. However, classification of thermal sensitivity at 42.5° depended on the time of heating, since thermal tolerance developed at different survival levels after 3 to 4 hr of heating for pig kidney, muntjac, Chinese hamster (V79 and CHO), and HeLa cells, whereas no thermal tolerance and only a transitory thermal tolerance were observed for mouse LP59 and rat kangaroo cells, respectively. Also, Chinese hamster ovary cells were more heat sensitive when cultured in McCoy's Medium 5a containing 10% calf serum plus 5% fetal calf serum than when cultured in F12 medium containing 10% fetal calf serum.

Small variations in the X-ray dose response of the seven mammalian cell lines (dose-modifying factors of less than 1.5) were observed. The X-ray response was enhanced by thermal treatment at 42.5° for 1 hr preceding irradiation, and there was a positive correlation between the degree of thermal enhancement and cellular thermal sensitivity at 42.5°. However, there was no correlation between differences in heat sensitivity and differences in radiosensitivity. Also, no apparent correlation between heat and/or X-ray response and cell chromosome number, DNA content, cell volume, and cell population doubling time could be found. However, heat sensitivity could, in general, be related to the body temperature of the species from which the cell line was derived.

¹ This work was supported by Grants CA08618 and CA18023 awarded by the National Cancer Institute, Department of Health, Education and Welfare, and a grant awarded to G. P. R. by the Medical Research Council of Canada.

² To whom requests for reprints should be addressed.

Received 7/10/78. Accepted 10/25/78.