Isolated brain microvessels as in vitro equivalents of the blood-brain barrier: selective removal by collagenase of the A-system of neutral amino acid transport.
On treatment with collagenase, brain microvessels, together with several protein components, lose some enzymatic activities such as alkaline phosphatase and gamma-glutamyltranspeptidase, whereas no change occurs in the activities of 5'-nucleotidase and glutamine synthetase. The energy-requiring "A-system" of polar neutral amino acid transport is also severely inactivated, whereas the L-system for the facilitated exchange of branched chain and aromatic amino acids is preserved. In the collagenase-digested microvessels, this leads to loss of the transtimulation effect of glutamine on the transport of large neutral amino acids, because such transtimulation is due to a cooperation between the A- and L-systems. By contrast, NH4+ maintains (and even enhances) its ability to stimulate the L-system of amino acid transport, presumably through glutamine synthesis within the endothelial cells.
D015720:5'-Nucleotidase; D000469:Alkaline Phosphatase / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001812:Blood-Brain Barrier; D001921:Brain / Q000098:blood supply*; D002196:Capillaries / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D002417:Cattle; D002463:Cell Membrane Permeability; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D007700:Kinetics; D003012:Microbial Collagenase / Q000494:pharmacology*; D008855:Microscopy, Electron, Scanning; D009708:Nucleotidases / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D005723:gamma-Glutamyltransferase / Q000378:metabolism
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D005904:Glial Fibrillary Acidic Protein; D000644:Quaternary Ammonium Compounds; C017911:2-(methylamino)isobutyric acid; D005723:gamma-Glutamyltransferase; D009708:Nucleotidases; D000469:Alkaline Phosphatase; D015720:5'-Nucleotidase; D003012:Microbial Collagenase; D005974:Glutamate-Ammonia Ligase