Time courses for the uptake of different amino acids. The data are from uninfected human erythrocytes (▴), arsenite-treated uninfected human erythrocytes (○), and P falciparum–infected human erythrocytes (●). The influx of L-[³H]-glutamate (A), D-[³H]-aspartate (B), D-[³H]-glutamate (C), and L-[³H]-alanine (D) was measured for a period of 20 minutes at 37°C. The cells were suspended in (glucose-free) PBS and in each case the radiolabeled compounds were the only extracellular amino acids present. The extracellular concentrations were 20nM for L-glutamate, 78nM for D-aspartate, 21nM for D-glutamate, and 13nM for L-alanine. The uptake data are expressed in terms of a distribution ratio (ie, the estimated concentration of radiolabel inside the cell relative to that in the extracellular solution). The data were averaged from 5 separate experiments performed on different days, on erythrocytes from different donors, and are shown ± SEM.