title: Inducible presynaptic glutamine transport supports glutamatergic transmission at the calyx of Held synapse.
abstract: The mechanisms by which the excitatory neurotransmitter glutamate is recycled at synapses are currently unknown. By examining the functional expression of plasma membrane transporters at presynaptic terminals, we aim to elucidate some of the mechanisms of glutamate recycling. Using whole-cell voltage-clamp recordings from rat calyx of Held presynaptic terminals, our data show, for the first time, that the glutamate precursor glutamine causes the direct activation of an electrogenic, sodium-dependent presynaptic transporter, which supplies glutamine for generation of presynaptic glutamate and helps sustain synaptic transmission. Interestingly, the functional expression of this transporter at the presynaptic plasma membrane is dynamically controlled by electrical activity of the terminal, indicating that uptake of neurotransmitter precursors is controlled by the demand at an individual terminal. Induction of the transporter current is calcium-dependent and inhibited by botulinum neurotoxin C, demonstrating the involvement of SNARE-dependent exocytosis in inserting transporters into the plasma membrane when the terminal is active. Conversely, inactivity of the presynaptic terminal results in removal of transporters via clathrin-mediated endocytosis. To investigate whether the presynaptic glutamine transporter supplies the precursor for generating the synaptically released glutamate, we measured miniature EPSCs to assess vesicular glutamate content. When the presynaptic glutamate pool was turned over by synaptic activity, inhibiting the presynaptic glutamine transporters with MeAIB reduced the miniature EPSC amplitude significantly. This demonstrates that presynaptic glutamine transport is centrally involved in the production of glutamate and assists in maintaining excitatory neurotransmission.
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom.
authors.forename: Daniela
authors.initials: D
authors.lastname: Billups
authors.forename: Mari-Carmen
authors.initials: MC
authors.lastname: Marx
authors.forename: Ioanna
authors.initials: I
authors.lastname: Mela
authors.forename: Brian
authors.initials: B
authors.lastname: Billups
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000502:physiology; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D001933:Brain Stem / Q000378:metabolism / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism / Q000502:physiology*; D005973:Glutamine / Q000096:biosynthesis* / Q000378:metabolism / Q000502:physiology; D008297:Male; D009924:Organ Culture Techniques; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000378:metabolism* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D015091:beta-Alanine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D026921:Amino Acid Transport Systems, Neutral; C403222:system N protein 1; D005973:Glutamine; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D018698:Glutamic Acid