Expression of GABA Receptor ρ1 and ρ2 Subunits in the Retina and Brain of the Rat

Abstract

We have investigated the distribution of GABA receptor ρ1 and ρ2 subunits in the rat central nervous system. Cloning of rat ρ1 and ρ2 cDNA fragments revealed similarities to the corresponding human sequences of 99% (ρ1) and 88% (ρ2) at the protein level. Whereas the human ρ2 subunit has no consensus sequence for phosphorylation by protein kinase C, the cytoplasmic loop of the rat sequence contains two such sites. Use of the polymerase chain reaction with reverse-transcribed total RNA (RT-PCR) from different brain tissues revealed that transcript for the ρ1 subunit was present in the retina only. The ρ2 mRNA was detected in all brain regions, with the highest level of expression in the retina. In situ hybridization of retinal sections revealed that ρ1 and ρ2 transcripts are present in the inner nuclear layer. RT-PCR and in situ hybridization of isolated retinal cells showed that both ρ subunits are present in rod bipolar cells. Since these cells express bicuculline-insensitive GABA receptors, our results further support the idea that ρ subunits are part of the GABA_C receptor.