The pH of the cytoplasm as an important factor in the survival of in vitro cultured malignant cells after hyperthermia. Effects of carbonylcyanide 3-chlorophenylhydrazone

Abstract

The effects of heat treatments at 43°C (hyperthermia), were studied on in vitro cultured cells, derived from a murine mammary carcinoma, at different pH values of the medium in the absence and presence of the proton conducting drug carbonylcyanide- 3-chlorophenylhydrazone (CCCP). The survival of these cells after hyperthermia was always optimal at a pH of the medium between 7.75 and 8.0. At this optimal pH the presence of CCCP hardly influenced the survival for treatment times up to 90 min, whereas there was a large effect of CCCP at lower pH values, pH 6.5–7.5. At higher pH values, 8.0–9.0 CCCP only had effect after at least 1 hr heating. For exposure times up to 3 hr CCCP only had a small effect at normal temperature, 37°C, except at very low pH values, below 6.5, where cell survival was impaired, even without CCCP. The large effect of CCCP in the pH range 6.5–7.5 strongly suggests that the survival after hyperthermia is mainly determined by the cytoplasm pH. Changes in the pH of the cell medium may affect survival only after modifying the cytoplasm pH. In the pH range 6.5–8.0 the cells are apparently able to maintain the optimal pH value inside, close to 8.0. The capacity to control pH is impaired by the addition of CCCP. Outside the range 6.5–8.0 the capacity to control pH appears to be insufficient or absent. Moreover it is presumed that there is a progressive deregulation of the pH control mechanism during a 43°C heat treatment. After 2 hr treatment at 43°C the cells apparently are no longer capable of maintaining their optimal cytoplasm pH.