The Glutamate–Aspartate Transporter GLAST Mediates Glutamate Uptake at Inner Hair Cell Afferent Synapses in the Mammalian Cochlea
Open Access
- 19 July 2006
- journal article
- Published by Society for Neuroscience in Journal of Neuroscience
- Vol. 26 (29), 7659-7664
- https://doi.org/10.1523/jneurosci.1545-06.2006
Abstract
Ribbon synapses formed between inner hair cells (IHCs) and afferent dendrites in the mammalian cochlea can sustain high rates of release, placing strong demands on glutamate clearance mechanisms. To investigate the role of transporters in glutamate removal at these synapses, we made whole-cell recordings from IHCs, afferent dendrites, and glial cells adjacent to IHCs [inner phalangeal cells (IPCs)] in whole-mount preparations of rat organ of Corti. Focal application of the transporter substrated-aspartate elicited inward currents in IPCs, which were larger in the presence of anions that permeate the transporter-associated anion channel and blocked by the transporter antagonistd,l-threo-β-benzyloxyaspartate. These currents were produced by glutamate–aspartate transporters (GLAST) (excitatory amino acid transporter 1) because they were weakly inhibited by dihydrokainate, an antagonist of glutamate transporter-1 (excitatory amino acid transporter 2) and were absent from IPCs inGLAST−/−cochleas. Furthermore,d-aspartate-induced currents in outside-out patches from IPCs exhibited larger steady-state currents than responses elicited byl-glutamate, a prominent feature of GLAST, and examination of cochlea from GLAST–Discosoma red (DsRed) promoter reporter mice revealed that DsRed expression was restricted to IPCs and other supporting cells surrounding IHCs. Saturation of transporters by photolysis of cagedd-aspartate failed to elicit transporter currents in IHCs, as did local application ofd-aspartate to afferent terminals, indicating that neither presynaptic nor postsynaptic membranes are major sites for glutamate removal. These data indicate that GLAST in supporting cells is responsible for transmitter uptake at IHC afferent synapses.Keywords
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