Figure 2.

Sulfonylurea-binding activity of AtMRP5 expressed in HEK293 cells. A, [³H]glibenclamide binding (fmol per 10⁶ cells) to whole HEK293 cells that have been mock transfected (n = 3) or transfected with AtMRP5 (n = 3) was measured 48 h after transfection. Mock, As in Figure 1A. B, Dissociation constant (K_d) value of [³H]glibenclamide binding to whole HEK293 cells transfected with AtMRP5. The amount of specific [³H]glibenclamide bound (fmol per 10⁶ cells) was plotted against the free [³H]glibenclamide concentration. Specific binding was determined by subtracting nonspecific binding measured in the presence of 1 μm unlabeled glibenclamide. Each point indicates the mean of three replicates. The line represents the best fit of a single-binding site model to the data. C, Inhibition of [³H]glibenclamide binding by tolbutamide. This was measured in the presence of 10 nm [³H]glibenclamide.