Figure 3
Uridine transport in Plasmodium falciparum -infected and uninfected human erythrocytes in the presence or absence of NPPB. A, B Uptake of 25 μM [3H]-uridine into P. falciparum-infected erythrocytes (closed symbols and dotted lines) and uninfected erythrocytes (open symbols, solid lines), expressed as pmol(107 cells)-1, was determined for the indicated times, at 22°C (A), or 8°C (B), respectively. Squares, no inhibitor; circles, 300 μM NPPB; triangles, 1 mM unlabelled uridine. Lines were calculated by linear regression and the results are the average of duplicate determinations. At 8 pmol(107 cells)-1, the intracellular concentration of uridine is estimated at 10.8 μM, using a published volume of 75 fL per infected erythrocyte [22]; thus, uridine has not reached equilibrium and linear rates of uptake are being measured over the interval of 9 s. C, Transport of 25 μM [3H]-uridine, expressed as pmol(107 cells)-1s-1, in uninfected human erythrocytes in the presence of various concentrations of NPPB (open circles) or unlabelled uridine (solid squares). Incubation time was 3 s and the experiment shown is representative of four independent experiments, each conducted in triplicate.