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The effect of hyperthermia on pH of cells cultivated at varying pH of the medium and under different conditions of oxygenation has been studied. Chinese hamster fibroblasts and pig embryo kidney cells were used. The intracellular pH (pHi) was determined by the microfluorimetric method using fluorescein diacetate. The required temperature (37 degrees C and 41 degrees C) was maintained by a warm stage in combination with a thermochamber. Different conditions of oxygenation were achieved by placing the cells into an open (euoxic) or closed (hypoxic) chamber. Both hyperthermia and hypoxia are shown to result in the acidification of cells. The effect increases with the duration of exposure to the agents used. The decrease of pHi is more pronounced when hyperthermia is combined with hypoxia or when the pH of the medium is low. The results obtained correlate with the magnitude of directly damaging and radiosensitizing effects of hyperthermia being dependent on the environmental conditions.

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