Thermal Tolerance and Repair of Thermal Damage by Cultured Cells

Abstract
Exposure of hamster cells to 42.5.degree. C for long periods leads to the development of thermal tolerance. The slope of the survival curve becomes shallower after .apprx. 3.5-4 h. If two 4 h exposures at 42.5.degree. C are separated by various periods of time, thermal tolerance is eliminated by 20 h. Prolonged exposure at 42.5.degree. C offers considerable protection from subsequent treatments to acute hyperthermia at 45.degree. C. Split exposures at 45.degree. C indicate a repair mechanism similar to that of X-rays. Posttreatment maintenance for 5 h at 4.degree. C or in conditioned medium or balanced salt solution failed to reveal any evidence of repair of potentially lethal damage. [This study is a model for cancer treatment.].