title: Expression of OCTN2 and OCTN3 in the apical membrane of rat renal cortex and medulla.
abstract: Immunological assays and transport measurements in apical membrane vesicles revealed that the apical membrane of rat kidney cortex and medulla presents OCTN2 and OCTN3 proteins and transports L-[(3)H]-carnitine in a Na(+)-dependent and -independent manner. OCTN2 mediates the Na(+)/L-carnitine transport activity measured in medulla because (i) the transport showed the same characteristics as the cortical Na(+)/L-carnitine transporter and (ii) the medulla expressed OCTN2 mRNA and protein. The Na(+)-independent L-carnitine transport activity appears to be mediated by both OCTN2 and OCTN3 since: (i) Na(+)-independent L-carnitine uptake was inhibited by both, anti-OCTN2 and anti-OCTN3 antibodies, (ii) kinetics studies revealed the involvement of a high- and a low-affinity transport systems, and (iii) Western and immunohistochemistry studies revealed that OCTN3 protein is located at the apical membrane of the kidney epithelia. The Na(+)-independent L-carnitine uptake exhibited trans-stimulation by intravesicular L-carnitine or betaine. This trans-stimulation was inhibited by anti-OCTN3 antibody, but not by anti-OCTN2 antibody, indicating that OCTN3 can function as an L-carnitine/organic compound exchanger. This is the first report showing a functional apical OCTN2 in the renal medulla and a functional apical OCTN3 in both renal cortex and medulla.
authors.affiliation: Facultad de Farmacia, Departamento de Fisiología y Zoología (Biomembranes Group), Universidad de Sevilla, 41012Sevilla, Spain.
authors.forename: M M
authors.initials: MM
authors.lastname: Cano
authors.forename: M L
authors.initials: ML
authors.lastname: Calonge
authors.forename: A A
authors.initials: AA
authors.lastname: Ilundain
mesh_terms: D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D001622:Betaine / Q000378:metabolism; D001693:Biological Transport, Active / Q000502:physiology; D002331:Carnitine / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D004847:Epithelial Cells / Q000378:metabolism* / Q000648:ultrastructure; D007150:Immunohistochemistry; D007684:Kidney Tubules / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D051379:Mice; D027701:Organic Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D000074058:Solute Carrier Family 22 Member 5; D022161:Transport Vesicles / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D019138:Antibodies, Blocking; D027701:Organic Cation Transport Proteins; D012333:RNA, Messenger; C498687:Slc22a21 protein, mouse; C115441:Slc22a5 protein, rat; D000074058:Solute Carrier Family 22 Member 5; D001622:Betaine; D012964:Sodium; D002331:Carnitine