Characterization of glycine release mediated by glycine transporter 1 stably expressed in HEK-293 cells.
We constructed a cell line which stably expresses glycine transporter 1 (GlyT1) proteins. The cell line showed significant [14C]glycine uptake and could keep steep glycine concentration gradient between intracellular and extracellular space (in > out). Using this cell line, we investigated glycine release mediated by this transporter. The [14C]glycine release was enhanced by extracellular glycine and sarcosine, a selective inhibitor of the transporter, in a dose-dependent manner. In addition, the replacement of extracellular Na+ with Li+ or extracellular Cl- with acetate- markedly increased the release. Furthermore, we investigated the effects of extracellular Ca2+ and K+. The removal of these ions also showed enhancement of the release. These results suggest that glycine transporter 1 protein, which might be involved in the NMDA receptor neurotransmission, can release glycine into the extracellular space in the vicinity of synapses, and that the release might be influenced by the extracellular substrate concentration and ion composition in the synaptic cleft.