Peak temperature influences on heating rate effect in hyperthermic cytotoxicity

Exponentially growing Chinese hamster V79 cells were heated from 37 degrees C up to 42 degrees C or 43 degrees C at four different heating rates: immediate exposure, 1/2 hour, 1 hour, and 2 hours. The D0's of the heat survival curves for both 42 degrees C and 43 degrees C were determined for the different heating rates. The results show that the decrease in toxicity to cells at 43 degrees C resulting from a slower heating rate appears to be less pronounced than that at 42 degrees C. However, the thermotolerance ratio is found to depend on the specific heating time (the reciprocal of the heating rate), in a linear fashion and it does not seem to depend on the peak temperature. We propose that the difference in the heat exchange on cell membranes at different rates of heating may contribute to the causes for the difference in cell sensitivity to hyperthermia.