title: Functional activity of L-carnitine transporters in human airway epithelial cells.
abstract: Carnitine plays a physiologically important role in the β-oxidation of fatty acids, facilitating the transport of long-chain fatty acids across the inner mitochondrial membrane. Distribution of carnitine within the body tissues is mainly performed by novel organic cation transporter (OCTN) family, including the isoforms OCTN1 (SLC22A4) and OCTN2 (SLC22A5) expressed in human. We performed here a characterization of carnitine transport in human airway epithelial cells A549, Calu-3, NCl-H441, and BEAS-2B, by means of an integrated approach combining data of mRNA/protein expression with the kinetic and inhibition analyses of L-[(3)H]carnitine transport. Carnitine uptake was strictly Na(+)-dependent in all cell models. In A549 and BEAS-2B cells, carnitine uptake was mediated by one high-affinity component (Km<2 μM) identifiable with OCTN2. In both these cell models, indeed, carnitine uptake was maximally inhibited by betaine and strongly reduced by SLC22A5/OCTN2 silencing. Conversely, Calu-3 and NCl-H441 exhibited both a high (Km~20 μM) and a low affinity (Km>1 mM) transport component. While the high affinity component is identifiable with OCTN2, the low affinity uptake is mediated by ATB(0,+), a Na(+), and Cl(-)-coupled transport system for neutral and cationic amino acids, as demonstrated by the inhibition by leucine and arginine, as well as by SLC6A14/ATB(0,+) silencing. The presence of this transporter leads to a massive accumulation of carnitine inside the cells and may be of peculiar relevance in pathologic conditions of carnitine deficiency, such as those associated to OCTN2 defects.
authors.affiliation: Dept. of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Ingoglia
authors.affiliation: Dept. of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy.
authors.forename: Rossana
authors.initials: R
authors.lastname: Visigalli
authors.affiliation: Dept. of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy.
authors.forename: Bianca Maria
authors.initials: BM
authors.lastname: Rotoli
authors.affiliation: Dept. of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy.
authors.forename: Amelia
authors.initials: A
authors.lastname: Barilli
authors.affiliation: Preclinical Pharmacokinetics, Biochemistry & Metabolism Dept., Chiesi Farmaceutici, Largo F. Belloli 11/A, 43122 Parma, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Riccardi
authors.affiliation: Preclinical Pharmacokinetics, Biochemistry & Metabolism Dept., Chiesi Farmaceutici, Largo F. Belloli 11/A, 43122 Parma, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Puccini
authors.affiliation: Dept. of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy. Electronic address: valeria.dallasta@unipr.it.
authors.forename: Valeria
authors.initials: V
authors.lastname: Dall'Asta
mesh_terms: D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics / Q000378:metabolism; D001693:Biological Transport, Active / Q000502:physiology; D002331:Carnitine / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D027701:Organic Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism*; D000074058:Solute Carrier Family 22 Member 5; D027981:Symporters
chemical_list: D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D027701:Organic Cation Transport Proteins; C109807:SLC22A4 protein, human; C492020:SLC22A5 protein, human; C503995:SLC6A14 protein, human; D000074058:Solute Carrier Family 22 Member 5; D027981:Symporters; D002331:Carnitine
keywords: ATB(0,+); Carnitine; OCTN1; OCTN2; Pulmonary epithelium