Effect of hyperthermia on intracellular pH in human U-87 MG glioblastoma cells

The effect of hyperthermia at 43 degrees C on intracellular pH (pHi) in human U-87 MG glioblastoma cells was studied by using the fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-pentaacetoxymethyl ester. The presence of Na+/H+ antiporter activity in the cells were demonstrated by the Na(+)-dependent increase in intracellular pH (pHi) after cellular acidification in the absence of HCO3-. Hyperthermia at 43 degrees C caused significant decrease in pHi. The acidification was readily reversible by cooling the cells back down to 37 degrees C. The pHi change was inhibited by the addition of 1 mM amiloride in the incubation medium. Amiloride and hyperthermia exhibited a synergistic effect in suppressing thymidine incorporation into the cells.