© 1998 International Society for Neurochemistry Glutamine Uptake at the Blood—Brain Barrier Is Mediated by N-System Transport

Abstract: The mechanism of unidirectional transport of glutamine from blood to brain in pentobarbital-anesthe-tized rats was examined using in Situ perfusion. Amino acid uptake into brain across the blood—brain barrier(BBB) is classically thought to be via the Na-independent large neutral (L-system), acidic and basic amino acid transporters. In the presence of physiological concentra-tions of amino acids in the perfusate, which should satu-rate the known amino acid transporters at the BBB, the cortical transfer constant (I<~)for L-[14C]glutamine was11.6 ± 1.1 ~tl/g/min.The addition of either 10 mM 2-amino-2-norbornanecarboxylic acid or 10 mM 2-amino-2-norbornanecarboxylic acid and 5 mM cysteine had no effect on the cortical K for L-[14C]glutamine, indicating that glutamine transport under these conditions does not occur by the L-, A-, or ASC-systems. Decreasing perfu-sate Na from 140 to 2.4 mM by Tris substitution reduce