Fig. 2.

Time course of net MTX uptake. R1-11-PCFT-h cells were washed twice with HBS (pH 7.4) or RPMI and preincubated in the respective buffers for 20 minutes in a 37°C water bath or in a CO₂ incubator, respectively. Cells were then exposed to HBS or RPMI containing [³H]MTX (100 μM) over 10–50 minutes in the presence or absence of 10 μM FCCP. Net uptake is expressed as units of picomoles per milligram protein (left Y-axis) or units of micromoles per liter of intracellular water (right Y-axis). The data are the mean ± S.D. from three independent experiments.