SNAT3‐mediated glutamine transport in perisynaptic astrocytes in situ is regulated by intracellular sodium. Issue 6 (8th March 2017)

• Record Type: Journal Article
• Authors: Todd, Alison C.; Marx, Mari‐Carmen; Hulme, Sarah R.; Bröer, Stefan; Billups, Brian
• Is Part Of: Glia. Volume 65:Issue 6(2017)
• Page Start: 900
• Page End: 916
• Publication Date: 2017-03-08
• Subjects: calyx of Held -- EAAT -- Slc38a3 -- system A -- system N; Neuroglia -- Periodicals; Neurology -- Periodicals; 611.0188
• DOI: 10.1002/glia.23133
• Languages: English
• ISSNs: 0894-1491

Abstract

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 pHi and Na i + . 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 ( K M of 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 + ]i would 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 Na i + signaling, as would be stimulated by neighboring synaptic activity, has the capacity to stimulate astrocytic glutamine release to support glutamate recycling. Main Points: Astrocytes in situ transport glutamine via the SNAT3 transporter. EAAT activation causes a rise in [Na + ]i, which alters the SNAT3 equilibrium to release glutamine. This links neuronal activity to the supply of a neurotransmitter precursor from glia.