Hyperthermic Inactivation of Diploid Yeast and the Interaction of Damage Caused by Hyperthermia and Ionizing Radiation

Summary

Inactivation of diploid yeast by hyperthermia has been studied. D₀ and D_q decrease with temperature for euoxic and anoxic conditions. The Arrhenius plot shows a break at 52°C; the inactivation energies above and below this temperature are 153 and 94 kcal/mol respectively.

Hyperthermia (20 min at 51°C) also potentiates the lethal action of gamma rays in diploid yeast cells under both euoxic and anoxic conditions. The interaction between hyperthermic and radiation damage appears to be largely at the sublethal level. In euoxic cells, the hyperthermic potentiation decreases with increasing time between the application of hyperthermia and radiation, being completely lost after 24 hours. However, in the anoxic cells there was no decrease in the hyperthermic potentiation with increasing time interval. These results suggest that yeast cells are capable of repairing hyperthermic sublethal damage, but require oxygen to do so. Thus there is a similarity in the process of repair of sublethal damage caused by ionizing radiation on the one hand and hyperthermia on the other.