Na+-coupled transport of l-carnitine via high-affinity carnitine transporter OCTN2 and its subcellular localization in kidney

Abstract

The mechanism of Na(+)-dependent transport of L-carnitine via the carnitine/organic cation transporter OCTN2 and the subcellular localization of OCTN2 in kidney were studied. Using plasma membrane vesicles prepared from HEK293 cells that were stably transfected with human OCTN2, transport of L-carnitine via human OCTN2 was characterized. Uptake of L-[(3)H]carnitine by the OCTN2-expressing membrane vesicles was significantly increased in the presence of an inwardly directed Na(+) gradient, with an overshoot, while such transient uphill transport was not observed in membrane vesicles from cells that were mock transfected with expression vector pcDNA3 alone. The uptake of L-[(3)H]carnitine was specifically dependent on Na(+) and the osmolarity effect showed that Na(+) significantly influenced the transport rather than the binding. Changes of inorganic anions in the extravesicular medium and of membrane potential by valinomycin altered the initial uptake activity of L-carnitine by OCTN2. In addition, the fluxes of L-carnitine and Na(+) were coupled with 1:1 stoichiometry. Accordingly, it was clarified that Na(+) is coupled with flux of L-carnitine and the flux is an electrogenic process. Furthermore, OCTN2 was localized on the apical membrane of renal tubular epithelial cells. These results clarified that OCTN2 is important for the concentrative reabsorption of L-carnitine after glomerular filtration in the kidney.

Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation

“…2) (Tamai et al, 1998;Tokuhiro et al, 2003;Lahjouji et al, 2004;Garrett et al, 2008). Octn2 and OCTN2 proteins are present on the brush border membrane vesicles from kidneys (Tamai et al, 2001a), placental syncytiotrophoblasts , and small intestine enterocytes , as well as the basolateral surface of epididymal cells (Rodríguez et al, 2002) (Table 4).…”

Pharmacological manipulation of L-carnitine transport into L6 cells with stable overexpression of human OCTN2

“…Loss of carnitine from the body is minimized by the Na + -dependent high affinity carnitine transporter OCTN2, which is primarily responsible for reabsorption of filtered carnitine in the kidney [5][6][7][8]. The importance of this carnitine transporter becomes apparent from the severe consequences of OCTN2-related disorders.…”

Regulation of Octn2 Transporter (SLC22A5) by Peroxisome Proliferator Activated Receptor Alpha

“…[1][2][3] OCTN2 (SLC22A5) is an Na ϩ -dependent, high-affinity (K m ϭ4 to 25 mM) carnitine transporter, 2,3) which serves to maintain carnitine levels in serum by functioning as a reabsorption transporter of carnitine after glomerular filtration. [4][5][6] It was reported that human and mouse OCTN1 transported carnitine, 1,7) whereas rat OCTN1 did not. 8) Human carnitine transporter CT2 and mouse OCTN3, which are present selectively in male reproductive tissues, 3,9) transport carnitine with high affinity (K m ϭ20 mM and 3 mM, respectively) in an Na ϩ -independent manner.…”