A polarized localization of amino acid/carnitine transporter B(0,+) (ATB(0,+)) in the blood-brain barrier.

Brain capillary endothelial cells control the uptake and efflux from the brain of many hydrophilic compounds due to highly specialized transporters often localized in a polarized way. Localization of Na(+)- and Cl(-)-dependent amino acid and carnitine transporter B(0,+) (ATB(0,+)) was studied in a co-culture of bovine brain capillary endothelial cells (BBCEC) grown on filters above astrocytes (an in vitro blood-brain barrier model). Immunoblotting and three-dimensional immunocytochemistry analysis with anti-B(0,+)antibodies demonstrated the presence of this transporter and its prevalent co-localization with P-glycoprotein i.e. at the apical side. The sensitivity of leucine uptake through the apical membrane to 2-aminobicyclo-[2.2.1]-heptane-2-carboxylic acid (BCH), D-serine as well as sodium and chloride replacement confirm the functioning of ATB(0,+) and suggests an important physiological role of ATB(0,+) in controlling the delivery of amino acids and carnitine to the brain.