Non-bicarbonate buffering of ascites tumor cells in the rat as titrated by strong acids

Buffer equations originally derived for blood were applied to the in vitro system "ascites tumor cells and ascitic fluid'. Non-bicarbonate buffer values beta(mmol x pH(-1) x 1(-1)) were determined experimentally by titration of ascites, cell free ascitic fluid and cell homogenates with NaOH in the absence of CO2. beta in ascitic fluid, in native ascites and in cell homogenate were beta (F) = 5.9, beta (A) = 16.4 and beta (H) = 24.9, respectively. Intracellular beta value beta (C) calculated from buffer equations depended on the ratio delta pHi/delta pHe. With delta pHi/delta pHe = 1, beta (C) was 38.8. The difference between beta (C) and beta (H) could be partly accounted for by differences in the cellular protein content. With delta pHi/delta pHe = 0.62 as in the presence of CO2, beta (C) becomes 62.6. In the presence of CO2 (see Albers et al., 1981), the extracellular buffering was higher and the intracellular buffering lower than the values titrated in the absence of CO2. It is concluded that in the presence of CO2 and/or HCO3- the apparent intracellular buffering of intact tumor cells results from non-bicarbonate buffering by cell proteins as well as from active or passive ionic exchanges with the extracellular fluid.