The Influence of Hypoxia and Acidity on the Hyperthermic Response of Malignant CellsIn Vitro

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Abstract
Colony formation of JB-1-E ]mouse-plasmacytoma] cells was studied after hyperthermic treatment (42.5.degree. C) at a pH of 6.4 or 7.2 under hypoxic and euoxic conditions. At a pH of 7.2 and normal O2 tension, there was a moderate decrease in colony formation with increasing duration of hyperthermic treatment (To = 65 min). This effect was slightly enhanced under hypoxic conditions (To = 36 min). The hyperthermic effect was enhanced to a greater degree when treatment was performed at a pH of 6.4 (To = 19 min), with no observable difference between hypoxia and euoxia. These findings indicate that environmental acidity is a determining factor in the hyperthermic effect. The hypoxic effect at a pH of 7.2 is probably due to a slight decrease in the intracellular pH caused by increased production of lactic acid.