Figure 1.

Time-dependent uptake and efflux of [¹⁴C]urate in multidrug resistance protein (MRP) 4 cells. To compare the urate uptake in human embryonic kidney (HEK)-MRP4 cells with that in control cells, cells were incubated for 15 s, 10 min, 20 min, 30 min and 2 h at 4 °C with HBSS diffusion medium containing 50 μM [¹⁴C]urate (a). After incubation of MRP4 and control cells with 50 μM [¹⁴C]urate for 30 min at 4 °C, efflux was tested by incubating the cells in HBSS efflux medium at 37 °C for 15 s, 2 min, 3 min, 5 min and 10 min (b). MRP4-mediated [¹⁴C]urate efflux was calculated by subtracting control cell levels (c).