Identification and functional expression of a novel ligand binding subunit of the inhibitory glycine receptor

By homology screening of a rat brain cDNA library we have identified a novel alpha subunit variant of the inhibitory glycine receptor, alpha 3. The deduced protein exhibits 82-83% amino acid identity to the previously characterized rat and human alpha 1 and alpha 2 subunit sequences. Upon heterologous expression in Xenopus laevis oocytes, the alpha 3 subunit formed functional agonist-gated chloride channels which displayed a low affinity for glycine and only small responses to taurine. Amplification of alpha 3 transcripts by polymerase chain reaction revealed high levels in spinal cord at later postnatal stages of development. These data indicate alpha subunit heterogeneity of the inhibitory glycine receptor in adult rats that may result in pharmacologically distinct receptor subtypes.