Inhibition of glutamine transport depletes glutamate and GABA neurotransmitter pools: further evidence for metabolic compartmentation.
The role of glutamine and alanine transport in the recycling of neurotransmitter glutamate was investigated in Guinea pig brain cortical tissue slices and prisms, and in cultured neuroblastoma and astrocyte cell lines. The ability of exogenous (2 mm) glutamine to displace 13C label supplied as [3-13C]pyruvate, [2-13C]acetate, l-[3-13C]lactate, or d-[1-13C]glucose was investigated using NMR spectroscopy. Glutamine transport was inhibited in slices under quiescent or depolarising conditions using histidine, which shares most transport routes with glutamine, or 2-(methylamino)isobutyric acid (MeAIB), a specific inhibitor of the neuronal system A. Glutamine mainly entered a large, slow turnover pool, probably located in neurons, which did not interact with the glutamate/glutamine neurotransmitter cycle. This uptake was inhibited by MeAIB. When [1-13C]glucose was used as substrate, glutamate/glutamine cycle turnover was inhibited by histidine but not MeAIB, suggesting that neuronal system A may not play a prominent role in neurotransmitter cycling. When transport was blocked by histidine under depolarising conditions, neurotransmitter pools were depleted, showing that glutamine transport is essential for maintenance of glutamate, GABA and alanine pools. Alanine labelling and release were decreased by histidine, showing that alanine was released from neurons and returned to astrocytes. The resultant implications for metabolic compartmentation and regulation of metabolism by transport processes are discussed.
Rae
Caroline
C
Discipline of Biochemistry, School of Molecular & Microbial Biosciences, The University of Sydney, New South Wales, Australia. c.rae@mmb.usyd.edu.au
Hare
Nathan
N
Bubb
William A
WA
McEwan
Sally R
SR
Bröer
Angelika
A
McQuillan
James A
JA
Balcar
Vladimir J
VJ
Conigrave
Arthur D
AD
Bröer
Stefan
S
D019342:Acetic Acid / Q000378:metabolism; D000409:Alanine / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology*; D002247:Carbon Isotopes; D002451:Cell Compartmentation; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005947:Glucose / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology; D006168:Guinea Pigs; D006639:Histidine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D019344:Lactic Acid / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009447:Neuroblastoma / Q000378:metabolism; D051381:Rats; D015091:beta-Alanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002247:Carbon Isotopes; D005973:Glutamine; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D019344:Lactic Acid; D018698:Glutamic Acid; D006639:Histidine; D005680:gamma-Aminobutyric Acid; D005947:Glucose; D000409:Alanine; D019342:Acetic Acid