A comparison of amino acid transport and ouabain binding in brain endothelium and salivary epithelium studied in vivo by rapid paired-tracer dilution.
Amino acid tmransport at the luminal side of brain capillary endothelium and the basal side of salivary epithelium were compared using a nondestructive, first-circulation, paired-tracer dilution method. In the brain, the reference molecule was an intravascular marker (Crone's method) whereas inthe salivary gland the reference was an extracellular marker of similar size to the test molecule. The unidirectional flux was related to a maximal uptake, U: U = 1 --test concentration/reference concentration Uptake and cross-inhibition experiments in brain suggest the presence of only a long-chain neutral L-amino acid transport system (leucine, phenyl-alanine, tryptophan, tyrosine, valine, methionine). In contrast, results in the salivary gland suggest 4 transport systems: 1. large neutral, 2. small neutral (alanine, serine), 3. basic (lysine) and 4. acidic (aspartic, glutamic). The same method was applied to localize binding sites. Ouabain bound very significantly to the salivary epithelium but not at all to the brain endothelium. The method described is of interest since it can be extended to any organ and possibly to man.
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D002415:Cats; D004285:Dogs; D004848:Epithelium / Q000378:metabolism; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology*; D012469:Salivary Glands / Q000378:metabolism*
D000596:Amino Acids; D010042:Ouabain