title: Uptake of 4-chloro-2-methylphenoxyacetic acid (MCPA) from the apical membrane of Caco-2 cells by the monocarboxylic acid transporter.
abstract: The cellular uptake mechanism of 4-chloro-2-methylphenoxyacetic acid (MCPA), a phenoxyacetic acid derivative, was investigated using Caco-2 epithelial cells. The cells were incubated with 50 microM MCPA at pH 6.0 and 37 degrees C, and the uptake of MCPA from the apical membranes was measured. The uptake of MCPA was significantly decreased by incubation at low temperature (4 degrees C) and markedly increased by lowering the extracellular pH. Pretreatment with a protonophore, carbonylcyanide-p-(trifluoromethoxy)phenylhydrazone (25 microM), or metabolic inhibitors, 2,4-dinitrophenol (1 mM) and sodium azide (10 mM), significantly decreased the uptake of MCPA by 53%, 45% and 48%, respectively. Coincubation of MCPA with 10 mM l-lactic acid or alpha-cyano-4-hydroxycinnamate, which is a substrate or an inhibitor of the monocarboxylic acid transporters (MCTs), significantly decreased the uptake of MCPA by 31% and 20%, respectively, and coincubation with benzoic acid profoundly decreased the uptake by 68%. In contrast, coincubation with succinic acid (a dicarboxylic acid) did not affect the uptake. Kinetic analysis of initial MCPA uptake suggested that MCPA is taken up via a carrier-mediated process [Km=1.37+/-0.15 mM, Vmax=115+/-6 nmol (mg protein)(-1) (3 min)(-1)]. Lineweaver-Burk plots show that benzoic acid competitively inhibits the uptake of MCPA with a Ki value of 4.68 +/-1.76 mM. A trans-stimulation effect on MCPA uptake was found in cells preloaded with benzoic acid. These results suggest that the uptake of MCPA from the apical membrane of Caco-2 cells is mainly mediated by common MCTs along with benzoic acid but also in part by l-lactic acid.
authors: Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, 1757 Ishikari-Tobetsu, Hokkaido 061-0293, Japan.
authors: Osamu
authors: O
authors: Kimura
authors: Kensuke
authors: K
authors: Tsukagoshi
authors: Tetsuya
authors: T
authors: Endo
mesh_terms: D019297:2,4-Dinitrophenol / Q000494:pharmacology; D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019817:Benzoic Acid / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000031:analogs & derivatives / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D003080:Cold Temperature; D003373:Coumaric Acids / Q000494:pharmacology; D006540:Herbicides / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism / Q000494:pharmacology; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism*; D019810:Sodium Azide / Q000494:pharmacology
chemical_list: D003373:Coumaric Acids; D006540:Herbicides; D027501:Monocarboxylic Acid Transporters; C108897:carbonylcyanide 4-trifluoromethoxyphenylhydrazone; C007175:alpha-cyano-4-hydroxycinnamate; D019344:Lactic Acid; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D019817:Benzoic Acid; D019810:Sodium Azide; D008456:2-Methyl-4-chlorophenoxyacetic Acid; D019297:2,4-Dinitrophenol