Figure 2.

Functional characterization of natural variants of OCT1. (A) Uptake of MPP⁺ in oocytes expressing the reference OCT1 and each of the 15 protein-altering OCT1 variants. (B) Recovery of function for six OCT1 variants with reduced or increased function. Dark-shaded columns represent uptake by variants; lighter-shaded columns represent uptake by variants changed to the OCT1 reference sequence at a single nucleotide position by site-directed mutagenesis. (C) Effect of double mutations on transporter function. X. laevis oocytes were injected with ≈50 ng of RNA. Uptake of MPP⁺ (0.9 μM unlabeled MPP⁺, 0.1 μM ³H-MPP⁺) was measured at room temperature after incubation for 1 h. Data are representative of experiments carried out with three different batches of oocytes. Each value represents mean ± SD from seven to nine oocytes.