Fig. 8.

Effect of increasing 1-methyl-4-phenylpyridinium (MPP) concentration on the kinetics of organic cation transporter 2 (OCT2)-mediated metformin transport. A: relationship between increasing metformin concentration and the rate of metformin transport, determined in the absence (0 µM; solid circles) and presence of unlabeled MPP (1, 3, and 5 µM; open symbols). Each point is the average ± SE of rates (calculated from 60-s net uptakes) of transport measured in three separate experiments, each performed in triplicate. Each rate was corrected for the influence of a first-order component of metformin accumulation (see Fig. 7), and the resulting profiles described by the Michaelis-Menten equation (solid black lines). B: Eadie-Hofstee transformations of the kinetic profiles for metformin transport shown in A.