GlyR Α2 Research Articles

Expression of glycine receptor and transporter on bullfrog retinal Müller cells

The expression of the glycine receptor (GlyR) α1, α2 and β subunits and glycine transporter (GlyT) on Müller cells was studied in bullfrog retina using double immunofluorescence labeling and confocal scanning microscopy. Double labeling of glial fibrillary acidic protein (GFAP), a specific marker for Müller cells, and the GlyR subunits showed that almost all Müller cells moderately expressed GlyR α1 and weakly GlyR β, whereas no immunoreactivity for GlyR α2 was observed. The labeling for GlyR α1 and GlyR β appeared in somata, major processes, endfeet and branchlets of the Müller cells. Müller cells were also GlyT1-labeled. Consistent with previous electrophysiological results, these findings suggest that Müller cells may be involved in modulation of glycinergic transmission by reciprocal interactions with retinal neurons through GlyR and GlyT.

Diversity of glycine receptors in the mouse retina: localization of the alpha2 subunit.

Gamma-aminobutyric acid (GABA) and glycine are the major inhibitory neurotransmitters in the retina, glycine being produced in approximately half of all amacrine cells. Whereas retinal cell types expressing the glycine receptor (GlyR) alpha1 and alpha3 subunits have been mapped, the role of the alpha2 subunit in retinal circuitry remains unclear. By using immunocytochemistry, we localized the alpha2 subunit in the inner plexiform layer (IPL) in brightly fluorescent puncta, which represent postsynaptically clustered GlyRs. This was shown by doubly labeling sections for GlyR alpha2 and bassoon (a presynaptic marker) or gephyrin (a postsynaptic marker). Synapses containing GlyR alpha2 were rarely found on ganglion cell dendrites but were observed on bipolar cell axon terminals and on amacrine cell processes. Recently, an amacrine cell type has been described that is immunopositive for glycine and for the vesicular glutamate transporter vGluT3. The processes of this cell type were presynaptic to GlyR alpha2 puncta, suggesting that vGluT3 amacrine cells release glycine. Double labeling of sections for GlyR alpha1 and GlyR alpha2 subunits showed that they are clustered at different synapses. In sections doubly labeled for GlyR alpha2 and GlyR alpha3, approximately one-third of the puncta were colocalized. The most abundant GlyR subtype in retina contains alpha3 subunits, followed by those containing GlyR alpha2 and GlyR alpha1 subunits.

Alternative splicing generates two isoforms of the α2 subunit of the inhibitory glycine receptor

The inhibitory glycine receptor (GlyR) is a ligand-gated chloride channel protein which displays developmental heterogeneity in the mammalian central nervous system. Here we describe 2 novel cDNA variants of the rat GlyR α2 subunit and demonstrate that alternative splicing generates these 2 isoforms. The deduced protein sequences (α2A and α2B) exhibit 99% identity with the previously characterized human α2 subunit. In situ hybridization revealed expression of both α2A und α2B mRNAs in the prenatal rat brain, suggesting that these variant proteins may have a role in synaptogenesis. Heterologous expression in Xenopus oocytes showed that the more abundantly expressed α2A subunit forms strychnine-sensitive ion channels which resemble human α2 subunit GlyRs in their electrophysiological properties.