title: Carnitine/organic cation transporter OCTN2-mediated transport of carnitine in primary-cultured epididymal epithelial cells.
abstract: Carnitine is essential for the acquisition of motility and maturation of spermatozoa in the epididymis, and is accumulated in epididymal fluid. In this study, carnitine transport into primary-cultured rat epididymal epithelial cells was characterized to clarify the nature of the transporter molecules involved. Uptake of carnitine by primary-cultured epididymal epithelial cells was time, Na(+) and concentration dependent. Kinetic analysis of carnitine uptake by the cells revealed the involvement of high- and low-affinity transport systems with Km values of 21 microM and 2.2 mM respectively. The uptake of carnitine by the cells was significantly reduced by inhibitors of carnitine/organic cation transporter (OCTN2), such as carnitine analogues and cationic compounds. In RT-PCR analysis, OCTN2 expression was detected. These results demonstrated that the high-affinity carnitine transporter OCTN2, which is localized at the basolateral membrane of epididymal epithelial cells, mediates carnitine supply into those cells from the systemic circulation as the first step of permeation from blood to spermatozoa.
authors.affiliation: Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamasaki, Noda, Chiba 278-8510, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kobayashi
authors.forename: Masanori
authors.initials: M
authors.lastname: Irokawa
authors.forename: Tomoji
authors.initials: T
authors.lastname: Maeda
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuji
authors.forename: Ikumi
authors.initials: I
authors.lastname: Tamai
mesh_terms: D000108:Acetylcarnitine / Q000494:pharmacology; D026905:Amino Acid Transport Systems; D000818:Animals; D001622:Betaine / Q000031:analogs & derivatives / Q000494:pharmacology; D001692:Biological Transport; D002331:Carnitine / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004822:Epididymis / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D007930:Leucine / Q000494:pharmacology; D008239:Lysine / Q000494:pharmacology; D008297:Male; D027701:Organic Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011738:Pyrilamine / Q000494:pharmacology; D011802:Quinidine / Q000494:pharmacology; D012313:RNA / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism; D000074058:Solute Carrier Family 22 Member 5; D013997:Time Factors
chemical_list: D026905:Amino Acid Transport Systems; D027701:Organic Cation Transport Proteins; C115441:Slc22a5 protein, rat; D000074058:Solute Carrier Family 22 Member 5; D001622:Betaine; C002889:gamma-butyrobetaine; D012313:RNA; D000108:Acetylcarnitine; D012964:Sodium; D007930:Leucine; D011738:Pyrilamine; D011802:Quinidine; D008239:Lysine; D002331:Carnitine