Fig. 7.
A comparison of steady-state MTX levels in cells in RPMI at pH 6.9 vs. 7.4 and the effects of FCCP, ouabain, EIPA, or monensin. The pH was decreased to 6.9 by lowering the bicarbonate concentration to 7.2 mM with the cells maintained in 5% CO2. Cells were incubated with 100 μM [3H]MTX for 40 minutes in the absence or presence of FCCP, ouabain, EIPA, monensin, or a combination of monensin and FCCP. The intracellular MTX level in RPMI (pH 7.3) is indicated as 100%. Data are the mean ± S.D. from three independent experiments.