Transient Thermal Tolerance: Cell Killing and Polymerase Activities

Chinese hamster ovary cells heated continuously at 42.2°C became transiently thermal tolerant between 4 and 15 hr of heating. During this interval, thermal tolerance was evident by a plateau in the response for both cell killing and cellular DNA polymerase-alpha and -beta activities. As heating continued beyond 15 hr, both cell killing and reduction in polymerase-beta activity began to occur again. About 5 hr later, after 20 hr of heating, the activity of polymerase-alpha also began to decrease, but at a rate about one-third that observed for polymerase-beta. As reported previously, there is a positive correlation between hyperthermic-induced cell killing and hyperthermic reduction in cellular polymerase-beta activity. However, the correlation is only temporal, and additional studies are needed to determine if cell death is indeed related to a certain reduction in polymerase-beta activity.