title: Carnitine/xenobiotics transporters in the human mammary gland epithelia, MCF12A.
abstract: The barrier function of the human mammary gland collapses if challenged with cationic drugs, causing their accumulation in milk. However, underlying molecular mechanisms are not well understood. To gain insight into the mechanism, we characterized transport of organic cations in the MCF12A human mammary gland epithelial cells, using carnitine and tetraethylammonium (TEA) as representative nutrient and xenobiotics probes, respectively. Our results show that the mammary gland cells express mRNA and proteins of human (h) novel organic cation transporters (OCTN) 1 and hOCTN2 (a Na+-dependent carnitine carrier with Na+-independent xenobiotics transport function), which belong to the solute carrier superfamily (SLC) of transporters. Other SLC OCTs such as hOCT1 and extraneuronal monoamine transporter (EMT)/hOCT3 are also expressed at mRNA levels, but hOCT2 was undetectable. We further showed mRNA expression of ATB0+ (an amino acid transporter with a Na+/Cl(-)-dependent carnitine transport activity), and Fly-like putative transporter 2/OCT6 (a splice variant of carnitine transporter 2: a testis-specific Na+-dependent carnitine transporter). TEA uptake was pH dependent. Carnitine uptake was dependent on Na+, and partly on Cl-, compatible with hOCTN2 and ATB0+ function. Modeling analyses predicted multiplicity of the uptake mechanisms with the high-affinity systems characterized by K(m) of 5.1 microM for carnitine and 1.6 mM for TEA, apparently similar to the reported hOCTN2 parameter for carnitine, and that of EMT/hOCT3 for TEA. Verapamil, cimetidine, carbamazepine, quinidine, and desipramine inhibited the carnitine uptake but required supratherapeutic concentrations, suggesting robustness of the carnitine uptake systems against xenobiotic challenge. Our findings suggest functional roles of a network of multiple SLC organic cation/nutrient transporters in human mammary gland drug transfer.
authors.affiliation: Division of Clinical Pharmacology and Toxicology, Department of Pediatrics, Research Institute, Hospital for Sick Children, 555 Univ. Ave., Toronto, Ontario, Canada M5G 1X8.
authors.forename: Bruce
authors.initials: B
authors.lastname: Kwok
authors.forename: Ariko
authors.initials: A
authors.lastname: Yamauchi
authors.forename: Ratheishan
authors.initials: R
authors.lastname: Rajesan
authors.forename: Lillian
authors.initials: L
authors.lastname: Chan
authors.forename: Upinder
authors.initials: U
authors.lastname: Dhillon
authors.forename: Wen
authors.initials: W
authors.lastname: Gao
authors.forename: Haibo
authors.initials: H
authors.lastname: Xu
authors.forename: Bernice
authors.initials: B
authors.lastname: Wang
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Takahashi
authors.forename: John
authors.initials: J
authors.lastname: Semple
authors.forename: Ikumi
authors.initials: I
authors.lastname: Tamai
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Nezu
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuji
authors.forename: Patricia
authors.initials: P
authors.lastname: Harper
authors.forename: Shinya
authors.initials: S
authors.lastname: Ito
mesh_terms: D002331:Carnitine / Q000493:pharmacokinetics*; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D042361:Mammary Glands, Human / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D027701:Organic Cation Transport Proteins / Q000378:metabolism*; D000074058:Solute Carrier Family 22 Member 5; D027981:Symporters; D014018:Tissue Distribution; D015262:Xenobiotics / Q000493:pharmacokinetics*
chemical_list: D027701:Organic Cation Transport Proteins; C109807:SLC22A4 protein, human; C492020:SLC22A5 protein, human; D000074058:Solute Carrier Family 22 Member 5; D027981:Symporters; D015262:Xenobiotics; D002331:Carnitine