Effect of CO2 and lactic acid on intracellular pH of ascites tumor cells

The effect of CO2 and of lactic acid (L.A.) on the extracellular (pHe) and intracellular pH (pHi) of ascites tumor cells (DS-carcinosarcoma) in rats was studied by in vitro equilibration of ascites with CO2 and alteration of lactic acid concentration. pHi was determined by the distribution of DMO. The effects of lactic acid and CO2 on pH were additive and could be expressed as pHe = 8.872 - 0.745 logPCO2 - 0.0355 (L.A.) (R = 0.867, n = 201) pHi = 8.218 - 0.436 logPCO2 - 0.0275 (L.A.) (R = 0.812, n = 143) delta pHi/delta pHe was dependent on the way pHe was changed: If the change in pHe was due to lactic acid, delta pHi/delta pHe was 0.91; if it was due to CO2 delta pHi/delta pHe was 0.625. pHi exceeded pHe if either PCO2 and/or the concentration of lactic acid was raised above a critical level. The results render it questionable to predict intracellular pH values within solid tumor from pH measurements within the extracellular fluid.