FIG. 3.

MRP4-mediated efflux of tenofovir (A) and GS-9148 (B). Control cells and cells transiently expressing human MRP4 were preloaded with 1 μM [³H]tenofovir disoproxil (A) or 5 μM [¹⁴C]GS-9131 (B) for 2 h. After preloading, cells were washed and incubated in fresh medium in the presence or absence of 30 μM efflux inhibitor MK-571 for an additional 90 min. The amount of retained intracellular and effluxed extracellular compound was determined from the radioactivity content in cell lysates and culture medium, respectively, and is expressed as the percentage of the initial amount of compound present in preloaded cells. The data are presented as means ± standard deviations from three independent experiments performed in duplicate. The statistical significance of the differences between MRP4-expressing cells and the other tested samples for both intracellular and extracellular compound was assessed using a two-tail paired t test. *, P < 0.05; **, P < 0.01.