Evidence for an asymmetrical uptake of L-carnitine in the blood-brain barrier in vitro.
The transport of L-carnitine (4-N-trimethylammonium-3-hydroxybutyric acid) was studied with a primary culture of porcine brain capillary endothelial cells (BCEC) as an in vitro model of the blood-brain barrier. The measurements with suspended cells and cell monolayers allowed to distinguish a polarized transport phenomena. The part of the BCEC cells exposed to the medium (apical membrane) accumulated carnitine by a sodium-independent, saturable (Km=28 microM) system, with k=0.018 min-1. Exposure of the basolateral part revealed a presence of a facilitated diffusion process. Carnitine uptake through the saturable system was inhibited by butyrobetaine. Acylcarnitines and choline have no effect on the carnitine accumulation in suspended cells, a process diminished by phenylalanine, leucine, and L system inhibitor. This points to the possibility that carnitine enters through the basolateral membrane using amino acid transporting systems. A different, novel system is postulated to operate in the apical part of the plasma membrane of BCEC.
Mroczkowska
J E
JE
The Nencki Institute of Experimental Biology, 3 Pasteur St., Warsaw, 02-093, Poland.
Galla
H J
HJ
Nalecz
M J
MJ
Nalecz
K A
KA
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001812:Blood-Brain Barrier; D002196:Capillaries; D002331:Carnitine / Q000031:analogs & derivatives / Q000493:pharmacokinetics* / Q000494:pharmacology; D002478:Cells, Cultured; D002560:Cerebrovascular Circulation; D002794:Choline / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D013552:Swine
D002794:Choline; D002331:Carnitine