Kinetics of glial glutamine efflux and the mechanism of neuronal uptake studied in vivo in mildly hyperammonemic rat brain.
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.
Kanamori
Keiko
K
Magnetic Resonance Spectroscopy Laboratory, Huntington Medical Research Institutes, Pasadena, California 91105, USA. kkanamori@hmri.org
Ross
Brian D
BD
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
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