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J. Vigh, E. Rozsa; Glycine Transporter 1 (GLYT1) Modulates GABA Release From Amacrine Cells via NMDA Receptors. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1210.
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© ARVO (1962-2015); The Authors (2016-present)
NMDA receptors become active only after all of their glycine- and glutamate-binding sites have been occupied simultaneously. D-serine serves as co-agonist for the NMDA receptor’s glycine-binding site in some brain regions, whereas glycine is the more likely candidate in others. In the retina, ambient D-serine has been shown to mediate the NMDA-component of ON-OFF (Gustafson et al, 2007) and ON ganglion cell responses (Kalbaugh et al, 2009). Glycine transporter 1 (GLYT1) is highly abundant in the retina, and it is known to influence NMDA receptor function in the CNS via controling ambient extracellular glycine levels. The objective of the present study was to elucidate if glycine transporter 1 (GLYT1) can modulate NMDA receptor signalling in GABAergic amacrine cells (ACs).
Goldfishretinal slices were prepared at room temperature in daylight conditions. NMDA receptors on ACs were activated by short, focal NMDA-puffs or by endogenous glutamate released from a single, depolarized bipolar cell (BC) axon terminal. NMDA receptor function was monitored directly via recording NMDA receptor-mediated currents from voltage-clamped ACs, or indirectly, recording NMDA receptor activation-triggered GABAergic IPSCs from BCs. ALX 5407 or ALX 1393 (selective and potent inhibitors of GLYT1 and GLYT2, respectively) were bath applied in the presence of strychnine.
Application of ALX 5407 increased the NMDA puff-evoked currents in ACs. The NMDA puff-evoked GABAergic IPSCs in BCs were also increased by ALX 5407. ALX 5407 but not ALX 1393 increased reciprocal, GABAergic feedback to BC terminals. Coincidentally, glycine puff-evoked glycine transporter-mediated currents in ACs were sensitive to ALX 5407, but not to ALX 1393.
In light-adapted retinal slice preparation, the glycine-binding sites of NMDA receptors located on GABAergic ACs are not saturated. GLYT1, presumably localized on glycinergic ACs, may control GABA release from GABAergic ACs by influencing the occupancy of the glycine-binding subunits of their NMDA receptors.
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