TUMORIGENIC-3T3 CELLS MAINTAIN AN ALKALINE INTRACELLULAR PH UNDER PHYSIOLOGICAL CONDITIONS

One of the earliest events in the response of mammalian cells to mitogens is activation of Na+/H+ exchange, which increases intracellular pH (pH(in)) in the absence of HCO-/3 or at external pH values below 7.2. The proliferative response can be blocked by preventing the pH(in) increase; yet, the proliferative response cannot be stimulated by artificially raising pH(in) with weak bases or high medium pH. These observations support the hypothesis that optimal pH(in) is a necessary, but not sufficient, component of the proliferative-response sequence. This hypothesis has recently been challenged by the observation that transfection of NIH 3T3 cells with yeast H+-ATPase renders them tumorigenic. Although previous measurements indicated that these transfected cells maintain a higher pH(in) in the absence of HCO-/3, whether H+-ATPase transfection raised the pH(in) under physiologically relevant conditions was not known. The current report shows that these transfected cells do maintain a higher pH(in) than control cells in the presence of HCO-/3, supporting the possibility that elevated pH(in) is a proliferative trigger in situ. We also show that these cells are serum-independent for growth and that they glycolyze much more rapidly than phenotypically normal cells.