Expression of GABA receptor rho 1 and rho 2 subunits in the retina and brain of the rat.

We have investigated the distribution of GABA receptor rho 1 and rho 2 subunits in the rat central nervous system. Cloning of rat rho 1 and rho 2 cDNA fragments revealed similarities to the corresponding human sequences of 99% (rho 1) and 88% (rho 2) at the protein level. Whereas the human rho 2 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 rho 1 subunit was present in the retina only. The rho 2 mRNA was detected in all brain regions, with the highest level of expression in the retina. In situ hybridization of retinal sections revealed that rho 1 and rho 2 transcripts are present in the inner nuclear layer. RT-PCR and in situ hybridization of isolated retinal cells showed that both rho subunits are present in rod bipolar cells. Since these cells express bicuculline-insensitive GABA receptors, our results further support the idea that rho subunits are part of the GABAc receptor.