Alanine metabolism, transport, and cycling in the brain

• Published in: Journal of neurochemistry Vol. 102; no. 6; pp. 1758 - 1770
• Main Authors: Bröer, Stefan, Bröer, Angelika, Hansen, Jonas T, Bubb, William A, Balcar, Vladimir J, Nasrallah, Fatima A, Garner, Brett, Rae, Caroline
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.09.2007; Blackwell Publishing Ltd; Blackwell
• Subjects: 13C NMR spectroscopy; Alanine - metabolism; Amino Acid Transport System y+ - antagonists & inhibitors; Amino Acid Transport System y+ - metabolism; Ammonia - metabolism; Animals; Animals, Newborn; Biochemistry; Biochemistry and metabolism; Biological and medical sciences; Biological Transport, Active - drug effects; Biological Transport, Active - physiology; Brain - metabolism; Brain Chemistry - drug effects; Brain Chemistry - physiology; C NMR spectroscopy; Carrier Proteins - antagonists & inhibitors; Carrier Proteins - metabolism; Cells, Cultured; Central nervous system; Cerebral circulation. Blood-brain barrier. Choroid plexus. Cerebrospinal fluid. Circumventricular organ. Meninges; Energy Metabolism - physiology; Enzyme Inhibitors - pharmacology; Fundamental and applied biological sciences. Psychology; Fusion Regulatory Protein 1, Light Chains; Glutamic Acid - metabolism; glutamine transport; Guinea Pigs; LAT2; Metabolism; Mice; Neurosciences; Neurotransmitter Agents - biosynthesis; Neurotransmitters; Nitrogen; nitrogen metabolism; NMR; Nuclear magnetic resonance; Oocytes; Organ Culture Techniques; Presynaptic Terminals - drug effects; Presynaptic Terminals - metabolism; Rats; Rodents; Synaptic Transmission - physiology; Synaptosomes; Vertebrates: nervous system and sense organs; Energy metabolism; Neuroglia; Biological transport; Central nervous system; 13C NMR spectroscopy; nitrogen metabolism; Encephalon; Guinea pig; Primary culture; Carrier; glutamine transport; Alanine; Glial cell; Rodentia; Astrocyte; Glutamate; LAT2; Ammonia; Vertebrata; Mammalia; Neuron; Excitatory aminoacid; Neurotransmitter; System L amino acid transporter; Glutamine
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2007.04654.x

Brain glutamate/glutamine cycling is incomplete without return of ammonia to glial cells. Previous studies suggest that alanine is an important carrier for ammonia transfer. In this study, we investigated alanine transport and metabolism in Guinea pig brain cortical tissue slices and prisms, in primary cultures of neurons and astrocytes, and in synaptosomes. Alanine uptake into astrocytes was largely mediated by system L isoform LAT2, whereas alanine uptake into neurons was mediated by Na⁺-dependent transporters with properties similar to system B⁰ isoform B⁰AT2. To investigate the role of alanine transport in metabolism, its uptake was inhibited in cortical tissue slices under depolarizing conditions using the system L transport inhibitors 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid and cycloleucine (1-aminocyclopentanecarboxylic acid; cLeu). The results indicated that alanine cycling occurs subsequent to glutamate/glutamine cycling and that a significant proportion of cycling occurs via amino acid transport system L. Our results show that system L isoform LAT2 is critical for alanine uptake into astrocytes. However, alanine does not provide any significant carbon for energy or neurotransmitter metabolism under the conditions studied.