Temporal association between alterations in proton extrusion and low pH adaptation

Cells which have been adapted to growth at low extracellular pH (pHe) typically develop both an upregulation of steady state intracellular pH (pHi) and an ability to develop thermotolerance to 42 degrees C hyperthermia. These properties were acquired at different times, however. Days were required at pHe = 6.70 for two cell lines to adapt to low pHe by the thermotolerance criterion, but both had elevated steady state pHi values after only 4 hours at pHe = 6.70. A better correlation with adaptation to low pHe (as defined by hyperthermia) was found with changes in proton extrusion and the rate of pHi recovery after cytosolic acidification.