Localization of organic cation/carnitine transporter (OCTN2) in cells forming the blood–brain barrier

Abstract

Carnitine β‐hydroxy‐γ‐(trimethylammonio)butyrate – a compound necessary in the peripheral tissues for a transfer of fatty acids for their oxidation within the cell, accumulates in the brain despite low β‐oxidation in this organ. In order to enter the brain, carnitine has to cross the blood–brain barrier formed by capillary endothelial cells which are in close interaction with astrocytes. Previous studies, demonstrating expression of mRNA coding two carnitine transporters – organic cation/carnitine transporter 2 (OCTN2) and B0,+ in endothelial cells, did not give any information on carnitine transporters polarity in endothelium. Therefore more detailed experiments were performed on expression and localization of a high affinity carnitine transporter OCTN2 in an in vitro model of the blood–brain barrier by real‐time PCR, western blot analysis, and immunocytochemistry. The amount of mRNA was comparable in endothelial cells and kidney, when referred to house‐keeping genes, it was, however, significantly lower in astrocytes. Polarity of OCTN2 localization was further studied in an in vitro model of the blood–brain barrier with use of anti‐OCTN2 antibodies. Z‐axis analysis of the confocal microscope pictures of endothelial cells, with anti‐P‐glycoprotein antibodies as the marker of apical membrane, showed OCTN2 localization at the basolateral membrane and in the cytoplasmic region in the vicinity of nuclei. Localization of OCTN2 suggest that carnitine can be also transported from the brain, playing an important role in removal of certain acyl esters.

The Poorly Membrane Permeable Antipsychotic Drugs Amisulpride and Sulpiride Are Substrates of the Organic Cation Transporters from the SLC22 Family

“…OCT1 and OCT2 have been previously show to be localized at the luminal side of the brain microvascular endothelial cells (15) and may mediate the uptake of both amisulpride and sulpiride from the blood into the endothelial cells. In bovine BMECs, OCTN2 is expressed at the basolateral membrane of the endothelium (47). OCTN2 can transport drugs in both directions across the plasma membrane (8).…”

l-Carnitine and Acetyl-l-carnitine Roles and Neuroprotection in Developing Brain

“…Uptake into brain also occurs primarily via the OCTN2 transporter [1, 44, 45]. There is evidence that the B 0,+ transporter, a Na + /Cl − dependent amino acid/carnitine transporter, also has a role in L-carnitine and acetyl-L-carnitine uptake into brain [44, 46–48], and into astrocytes [49, 50]. Immunohistochemical studies show that labeling for OCTN 1, 2 and 3 is distributed in many regions of mouse brain and spinal cord in a pattern consistent with possible roles in modulating bioenergetics and cholinergic neurotransmission [51].…”

Effect of In Vivo l-Acetylcarnitine Administration on ATP-ases Enzyme Systems of Synaptic Plasma Membranes from Rat Cerebral Cortex

“…-dependent cation/carnitine transporter and to a lesser extent via the B(0,?) amino acid transporter [6][7][8]; in particular, the drug has a brain uptake index of 2.4 ± 0.2, which is similar to that of GABA, indicating an affinity of L-acetylcarnitine for the GABA transport system [9].…”