Hyperthermic Effect on Exponential and Plateau Ascites Tumor Cells in Vitro Dependent on Environmental pH

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Abstract
Colony formation of tumor cells obtained from asynchronous exponential and plateau growth PNJ ascites [mouse mammary] tumors were studied after hyperthermic treatment (42.degree. C) at pH 6.4 and 7.2 under normal O2 tension. At pH 7.2 plateau cells were more sensitive to heat than exponential cells. A pronounced increase in hyperthermic cell killing of exponential cells was found when the pH was changed from 7.2 to 6.4. Plateau cells were more sensitive to heat at pH 6.4 then at 7.2, but the relative decrease in cell survival was considerably less than in exponential cells. At pH 6.4 the plateau cells were still slightly more sensitive to heat than similarly treated exponential PNJ cells. An essential cause of the different effect of moderate hyperthermia on cells from exponential and plateau growth PNJ ascites tumors seems to be the different environment acidity but the possibility of a slightly increased heat sensitivity of plateau phase cells per se cannot be excluded.