title: Characterization of the transport of the organic cation [3H]MPP+ in human intestinal epithelial (Caco-2) cells.
abstract: The aim of this study was to characterize the transport of organic cations at the intestinal level, by studying the characteristics of the transport of 1-methyl-4-phenylpyridinium (MPP+) in Caco-2 cells. Transepithelial flux as well as cellular accumulation of [3H]MPP+ were quantitatively similar when substrate was applied from the basolateral or apical cell membrane. Verapamil (100 microM) and rhodamine123 (10 microM) significantly reduced [3H]MPP+ transepithelial flux in the apical-to-basolateral direction. When cells were grown on plastic supports, [3H]MPP+ was rapidly accumulated in the cells, both by saturable and nonsaturable mechanisms. The kinetic parameters of the saturable component were: Km: 449 microM and Vmax: 2,249 pmol per mg protein and 5 min. Uptake of [3H]MPP+ was metabolic energy-dependent and Na+-, pH- and potential-independent. It was inhibited by several organic cations (verapamil, rhodamine123, daunomycin, vinblastine, tetrabutylammonium and vecuronium) but not by others (tetraethylammonium and N-methylnicotinamide). Decynium22 and corticosterone inhibited [3H]MPP+ uptake into the cells. The P-glycoprotein antibody UIC2 (20 microg/ml) had no effect. In conclusion, [3H]MPP+ is efficiently transported by Caco-2 cells in both basolateral-to-apical (secretion) and apical-to-basolateral (absorption) directions. Absorption of [3H]MPP+ at the apical membrane seems to occur through a carrier-mediated mechanism belonging to the Amphiphilic Solute Facilitator (ASF) family of transporters, but distinct from the known members of this family.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Porto, Portugal. fatima_martel@hotmail.com
authors.forename: F
authors.initials: F
authors.lastname: Martel
authors.forename: C
authors.initials: C
authors.lastname: Calhau
authors.forename: I
authors.initials: I
authors.lastname: Azevedo
mesh_terms: D015655:1-Methyl-4-phenylpyridinium / Q000378:metabolism*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells; D002121:Calcium Channel Blockers; D002412:Cations / Q000378:metabolism; D003630:Daunorubicin / Q000494:pharmacology; D004347:Drug Interactions; D006540:Herbicides / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D012964:Sodium / Q000378:metabolism; D013997:Time Factors; D014316:Tritium; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000903:Antibiotics, Antineoplastic; D002121:Calcium Channel Blockers; D002412:Cations; D006540:Herbicides; D014316:Tritium; D012964:Sodium; D014700:Verapamil; D015655:1-Methyl-4-phenylpyridinium; D003630:Daunorubicin