Fig. 6.

Influence of substrate on the inhibition of OCT2-mediated transport produced by irinotecan. (A) Effect of increasing the irinotecan concentration on OCT2-mediated transport of [¹⁴C] metformin (16 µM; solid squares) or [³H]MPP (15 nM; solid circles). Each point is the mean rate of transport measured at each inhibitor concentration (normalized to transport measured in the absence of inhibitor; “% control”) measured in two separate experiments (±S.E.; n = 2), each determined in four replicate wells. (B) Data from Fig. 4A, plus the IC₅₀ profiles for irinotecan inhibition of [³H]TEA (20 nM; open diamonds), NBD-MTMA (3 µM; open circles), and ASP (10 µM; open triangles); error bars removed for clarity.