Purpose: The purpose of the present study is to examine the selectivity of various inhibitors towards the rat organic anion transporting polypeptides 1 (Oatp1: gene symbol Slc21a1) and 2 (Oatp2: Slc21a5).
Methods: The inhibitory effects of 20 compounds on the Oatpl-mediated transport of estradiol 17beta-D-glucuronide and on the Oatp2-mediated transport of digoxin were examined in cDNA-transfected LLC-PK1cells.
Results: Among the compounds examined in this study, nonsteroidal anti-inflammatory drugs, deoxycorticosterone. and quinidine preferentially inhibited Oatpl. whereas digoxin, quinine, and rifampicin preferentially inhibited Oatp2 at low concentrations. On the other hand, propionic acid, re-ketoglutarate and p-aminohippurate showed no inhibitory effects on either transporter up to a concentration of 1,000 microM. The Ki values of ibuprofen and quinidine were estimated to be 19 and 13 times lower for Oatpl compared with Oatp2, whereas the values for rifampicin, quinine, and digoxin were 13, 20, and 100< times lower for Oatp2 compared with Oatpl.
Conclusions: At low concentrations, some of the tested inhibitors exert selective inhibition of either Oatpl- or Oatp2-mediated substrate transport. These selective inhibitors may be used at appropriate concentrations to estimate the maximum contribution of Oatp1 or Oatp2 to the total substrate uptake into rat hepatocytes.