The influence of hyperthermia on the survival of irradiated yeast cells of different species has been studied. The experiments reported in the paper have shown: (1) simultaneous action of ionizing radiation and high temperatures appeared to increase the radiation response by a factor of approximately 2.7 for diploid and only by a factor of 1.5 for haploid cells of wild-type; (2) the combined action of high temperature and ionizing radiation had no synergistic effect for rad51 mutant diploid yeast cells; (3) heating before or after irradiation did not alter the radiation response of yeast cells; (4) enhancement of yeast cell sensitivity by simultaneous action of hyperthermia and 239Pu-alpha-particles was negligible; (5) the magnitude and the rate of liquid holding recovery is lowered with increasing of irradiation temperature. On this basis, it was concluded that possible mechanism for thermal sensitization of yeast cells may involve the reduced capacity of cells to recover damages resulted from the combined action of both modalities.
Experiments were carried out to determine the effects of hyperthermia alone or combined with gamma-rays on the survival of yeast cells of different species. Arrhenius plots for the heat inactivation of yeast cells show inflection points. This suggests that hyperthermic killing above or below these temperatures is mediated by different mechanisms. The synergism between hyperthermia and ionizing radiation was almost linearly dependent on temperature as shown by Arrhenius plots for the combined action of both modalities. The data obtained may imply that different processes are involved in heat inactivation and thermal enhancement of yeast cell radiosensitivity.
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