Effect of pH on hyperthermic cell survival.

Chinese hamster ovary cells incubated with various concentrations of CO2, to obtain extracellular pH values in the range of 6.40-7.85, were heated at 45.5C for 5, 10, or 20 minutes. Thermal sensitivity increased sharply from pH 7.35 to 6.65 (i.e., survival decreased from 1 X 10(-2) to 3 X 10(-5) for 20 minutes of heating), but remained constant from pH 7.35 to 7.85. The enhanced thermal sensitivity at pH values below pth 7.35 suggested that tumors should be preferentially destroyed by heat relative to normal tissue, since reports indicated that tumors were more acidic than the surrounding normal tissue.