We previously evaluated the renal excretion mechanism of quinidine, which is a tertiary amine compound, using porcine kidney epithelial LLC-PK 1 cells and P-glycoprotein (P-gp)-expressed LLC-GA5-COL150 cells.1) The transepithelial transport of quinidine in the basolateral-to-apical direction in LLC-PK 1 cells was similar to that in the opposite direction. In contrast, quinidine was transported actively in the basolateral-to-apical direction in LLC-GA5-COL150 cells. The results suggested that P-gp is mainly responsible for the tubular secretion of quinidine in the kidney. 1) We also evaluated the intestinal absorption mechanism of quinidine using human intestinal epithelial Caco-2 cells.2) The temperaturedependent uptake of quinidine in Caco-2 cells grown on a plastic dish was increased by alkalization of the apical medium, and was inhibited by diphenhydramine and imipramine. The results suggested that a cation transport system was involved in the influx of quinidine at the apical membrane in intestinal epithelial cells. 2)Procainamide, another tertiary amine compound with a pK a value of 9.23, is classified as a type IA antiarrhythmic drug that works by decreasing conduction velocity, and prolonging tissue refractoriness.3) More than 80% of orally administered procainamide is absorbed from the intestine in humans.4) The Kp (octanol/buffer at pH 7.4) value of procainamide is about 0.1, and approximately half of the dose is excreted in the urine as unchanged drug.3-6) However, the mechanisms responsible for the membrane transport of procainamide in intestinal and renal epithelial cells are still unclear.In the present study, the transport characteristics of procainamide in LLC-PK 1 cells were compared with those of quinidine. In addition, we evaluated whether the transport system for quinidine is present in another intestinal cell line, LS180, as well as Caco-2. We also investigated whether the transport system of procainamide in LS180 cells is the same as that of quinidine. Cell Culture and Preparation of Monolayers LLC-PK 1 cells at passage 197 and LS180 cells at passage 38 were obtained from the American Type Culture Collection (Manassas, VA, U.S.A.). These cells were maintained by serial passage in plastic dishes with Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum (Biowest Inc., Nuaille, France) in an atmosphere of 5% CO 2 -95% air at 37°C. MATERIALS AND METHODS MaterialsLLC-PK 1 cells were seeded at a density of 5ϫ10 5 cells/ cm 2 on a 1.12 cm 2 porous membrane (3 mm pore size) in a polyester membrane Transwell ® -Clear insert (Costar, Cambridge, MA, U.S.A.) to evaluate the transcellular transport of cationic drugs. The seeded cells were maintained for 6 d to prepare differentiated cell monolayers. The maturity of the monolayer was judged by transepithelial electrical resistance (TEER). TEER was measured using a Millicell-ERS resistance system (Millipore, Bedford, MA, U.S.A.). LLC-PK 1 cell monolayers whose TEER was above 60 W · cm 2 were used to The aim of the present study was t...

The aim of the present study was to investigate the mechanisms for membrane transport of metformin in human intestinal epithelial Caco-2 cells. The mRNA of not only organic cation transporter (OCT) 3, but also OCT1 and OCT2, was expressed in Caco-2 cells. The uptake of 100 µm metformin at the apical membrane of Caco-2 cells grown on porous filter membrane was significantly greater than that at the basolateral membrane. The apical uptake of 100 µm metformin in Caco-2 cells grown on plastic dishes was inhibited significantly by 1 mm unlabeled metformin, quinidine and pyrilamine, indicating that a specific transport system is involved in the apical uptake of metformin in Caco-2 cells. The apical uptake of 100 µm metformin in Caco-2 cells was decreased by acidification of the medium, but not increased by alkalization. In addition, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (a protonophore) had no effect on the apical uptake of metformin in Caco-2 cells at apical medium pH 8.4. These findings suggested that the apical uptake of metformin in Caco-2 cells is mediated at least partly by OCTs, but that the postulated H(+) /tertiary amine antiport system is not responsible for the apical uptake of metformin.

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