title: SNAT3-mediated glutamine transport in perisynaptic astrocytes in situ is regulated by intracellular sodium.
abstract: The release of glutamine from astrocytes adjacent to synapses in the central nervous system is thought to play a vital role in the mechanism of glutamate recycling and is therefore important for maintaining excitatory neurotransmission. Here we investigate the nature of astrocytic membrane transport of glutamine in rat brainstem slices, using electrophysiological recording and fluorescent imaging of pHiand Nai+. Glutamine application to perisynaptic astrocytes induced a membrane current, caused by activation of system A (SA) family transporters. A significant electroneutral component was also observed, which was mediated by the system N (SN) family transporters. This response was stimulated by glutamine (KMof 1.57 mM), histidine, and asparagine, but not by leucine or serine, indicating activation of the SNAT3 isoform of SN. We hypothesized that increasing the [Na+]iwould alter the SNAT3 transporter equilibrium, thereby stimulating glutamine release. In support of this hypothesis, we show that SNAT3 transport can be driven by changing cation concentration and that manipulations to raise [Na+]i(activation of excitatory amino acid transporters (EAATs), SA transporters or AMPA receptors) all directly influence SNAT3 transport rate. A kinetic model of glutamine fluxes is presented, which shows that EAAT activation causes the release of glutamine, driven mainly by the increased [Na+]i. These data demonstrate that SNAT3 is functionally active in perisynaptic astrocytes in situ. As a result, astrocytic Nai+ signaling, as would be stimulated by neighboring synaptic activity, has the capacity to stimulate astrocytic glutamine release to support glutamate recycling.
authors.affiliation: Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra, ACT 2601, Australia.|Centre for Integrative Physiology, School of Biomedical Sciences, University of Edinburgh, Edinburgh, EH8 9XD, United Kingdom.
authors.forename: Alison C
authors.identifier: 0000-0001-6318-5987
authors.initials: AC
authors.lastname: Todd
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1BT, United Kingdom.
authors.forename: Mari-Carmen
authors.initials: MC
authors.lastname: Marx
authors.affiliation: Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra, ACT 2601, Australia.
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Hulme
authors.affiliation: Research School of Biology, The Australian National University, Linnaeus Way 134, Canberra, ACT 2601, Australia.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bröer
authors.affiliation: Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra, ACT 2601, Australia.
authors.forename: Brian
authors.identifier: 0000-0001-5378-2809
authors.initials: B
authors.lastname: Billups
mesh_terms: D026924:Amino Acid Transport System A / Q000378:metabolism; D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001933:Brain Stem / Q000187:drug effects / Q000378:metabolism; D002414:Cations, Monovalent / Q000378:metabolism; D005260:Female; D050491:Glutamate Plasma Membrane Transport Proteins / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008094:Lithium / Q000378:metabolism; D008297:Male; D008959:Models, Neurological; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D046509:Tissue Culture Techniques
chemical_list: D026924:Amino Acid Transport System A; D026921:Amino Acid Transport Systems, Neutral; D002414:Cations, Monovalent; D050491:Glutamate Plasma Membrane Transport Proteins; D018091:Receptors, AMPA; C403222:system N protein 1; D005973:Glutamine; D008094:Lithium; D012964:Sodium
keywords: EAAT; Slc38a3; calyx of Held; system A; system N