title: Cotransport of reduced glutathione with bile salts by MRP4 (ABCC4) localized to the basolateral hepatocyte membrane.
abstract: The liver is the major source of reduced glutathione (GSH) in blood plasma. The transport protein mediating the efflux of GSH across the basolateral membrane of human hepatocytes has not been identified so far. In this study we have localized the multidrug resistance protein 4 (MRP4; ABCC4) to the basolateral membrane of human, rat, and mouse hepatocytes and human hepatoma HepG2 cells. Recombinant human MRP4, expressed in V79 hamster fibroblasts and studied in membrane vesicles, mediated ATP-dependent cotransport of GSH or S-methyl-glutathione together with cholyltaurine, cholylglycine, or cholate. Several monoanionic bile salts and the quinoline derivative MK571 were potent inhibitors of this unidirectional transport. The K(m) values were 2.7 mmol/L for GSH and 1.2 mmol/L for the nonreducing S-methyl-glutathione in the presence of 5 micromol/L cholyltaurine, and 3.8 micromol/L for cholyltaurine in the presence of 5 mmol/L S-methyl-glutathione. Transport of bile salts by MRP4 was negligible in the absence of ATP or without S-methyl-glutathione. These findings identify a novel pathway for the efflux of GSH across the basolateral hepatocyte membrane into blood where it may serve as an antioxidant and as a source of cysteine for other organs. Moreover, MRP4-mediated bile salt transport across the basolateral membrane may function as an overflow pathway during impaired bile salt secretion across the canalicular membrane into bile. In conclusion, MRP4 can mediate the efflux of GSH from hepatocytes into blood by cotransport with monoanionic bile salts.
authors.affiliation: Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Rius
authors.forename: Anne T
authors.initials: AT
authors.lastname: Nies
authors.forename: Johanna
authors.initials: J
authors.lastname: Hummel-Eisenbeiss
authors.forename: Gabriele
authors.initials: G
authors.lastname: Jedlitschky
authors.forename: Dietrich
authors.initials: D
authors.lastname: Keppler
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D006528:Carcinoma, Hepatocellular; D016764:Cell Polarity / Q000502:physiology; D002756:Cholagogues and Choleretics / Q000493:pharmacokinetics*; D006224:Cricetinae; D005347:Fibroblasts; D015870:Gene Expression; D005978:Glutathione / Q000031:analogs & derivatives* / Q000493:pharmacokinetics* / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D008113:Liver Neoplasms; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051381:Rats; D013656:Taurocholic Acid / Q000493:pharmacokinetics*; D014162:Transfection; D022161:Transport Vesicles / Q000378:metabolism; D014316:Tritium
chemical_list: D000255:Adenosine Triphosphate; D000906:Antibodies; D002756:Cholagogues and Choleretics; D005978:Glutathione; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D013656:Taurocholic Acid; D014316:Tritium; C073492:ABCC4 protein, human; C489540:Abcc4 protein, mouse; C489542:Abcc4 protein, rat; C114462:multidrug resistance-associated protein 3; C017514:S-methyl glutathione