title: Kinetics of glial glutamine efflux and the mechanism of neuronal uptake studied in vivo in mildly hyperammonemic rat brain.
abstract: Kinetics of glial glutamine (GLN) transport to the extracellular fluid (ECF) and the mechanism of GLN(ECF) transport into the neuron--crucial pathways in the glutamine-glutamate cycle--were studied in vivo in mildly hyperammonemic rat brain, by NMR and microdialysis to monitor intra- and extracellular GLN. The minimum rate of glial GLN efflux, determined from the rate of GLN(ECF) increase during perfusion of alpha-(methylamino)isobutyrate (MeAIB), which inhibits neuronal GLN(ECF) uptake by sodium-coupled amino-acid transporter (SAT), was 2.88 +/- 0.22 micromol/g/h at steady-state brain [GLN] of 8.5 +/- 0.8 micromol/g. Our previous study showed that the rate of glutamine synthesis under identical experimental conditions was 3.3 +/- 0.3 micromol/g/h. At steady-state glial [GLN], this is equal to its efflux rate to the ECF. Comparison of the two rates suggests that SAT mediates at least 87 +/- 8% (= 2.88/3.3 x 100%) of neuronal GLN(ECF) uptake. While MeAIB induced > 2-fold elevation of GLN(ECF), no sustained elevation was observed during perfusion of the selective inhibitor of LAT, 2-amino-bicyclo[1,1,2]heptane-2-carboxylic acid (BCH), or of d-threonine, a putative selective inhibitor of ASCT2-mediated GLN uptake. The results strongly suggest that SAT is the predominant mediator of neuronal GLN(ECF) uptake in adult rat brain in vivo.
authors.affiliation: Magnetic Resonance Spectroscopy Laboratory, Huntington Medical Research Institutes, Pasadena, California 91105, USA. kkanamori@hmri.org
authors.forename: Keiko
authors.initials: K
authors.lastname: Kanamori
authors.forename: Brian D
authors.initials: BD
authors.lastname: Ross
mesh_terms: D026924:Amino Acid Transport System A / Q000037:antagonists & inhibitors / Q000378:metabolism; D026962:Amino Acid Transport System ASC / Q000037:antagonists & inhibitors / Q000378:metabolism; D027182:Amino Acid Transport System y+ / Q000037:antagonists & inhibitors / Q000378:metabolism; D026905:Amino Acid Transport Systems / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000503:physiopathology; D002450:Cell Communication / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D045604:Extracellular Fluid / Q000378:metabolism; D027301:Fusion Regulatory Protein 1, Light Chains / Q000378:metabolism; D018698:Glutamic Acid / Q000096:biosynthesis*; D005973:Glutamine / Q000378:metabolism*; D022124:Hyperammonemia / Q000378:metabolism / Q000503:physiopathology; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D017551:Microdialysis; D015778:Minor Histocompatibility Antigens; D009457:Neuroglia / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D026924:Amino Acid Transport System A; D026962:Amino Acid Transport System ASC; D027182:Amino Acid Transport System y+; D026905:Amino Acid Transport Systems; D004791:Enzyme Inhibitors; D027301:Fusion Regulatory Protein 1, Light Chains; D015778:Minor Histocompatibility Antigens; C498850:Slc1a5 protein, mouse; C486716:Slc38a1 protein, rat; C412568:Slc38a2 protein, rat; C486582:Slc7a8 protein, rat; D005973:Glutamine; D018698:Glutamic Acid