Identification of the gamma-aminobutyric acid receptor beta(2) and beta(3) subunits in rat, rabbit, and human kidneys.

The properties and functions of gamma-aminobutyric acid (GABA(A)) receptors in the mammalian central nervous system are well studied. However, the presence and significance of GABA(A) receptors in nonneural tissue is less clear. The goal of this study was to examine the expression and localization of the GABA(A) receptor beta(2) and beta(3) subunits in the kidney. Reverse transcriptase products from RNA isolated from rat and rabbit kidney cortex and cerebellum and rabbit S(2) segments were amplified by use of PCR and GABA(A) beta(2) and beta(3) subunit-specific primers. Sequencing of the kidney PCR products revealed that the rat kidney cortex and rat neuronal GABA(A) receptor beta(2) subunit were identical in nucleotide composition. The rabbit kidney and rabbit neuronal GABA(A) receptor beta(2) subunit were 99% identical in nucleotide composition. Sequencing of the kidney PCR products revealed that the rat kidney cortex and rat neuronal GABA(A) receptor beta(3) subunits were 93% and 95% identical in nucleotide and amino acid composition, and rabbit kidney cortex and rabbit neuronal GABA(A) receptor beta(3) subunits were 95% and 98% identical in nucleotide and amino acid composition, respectively. PCR screening of a human kidney cDNA library and sequencing revealed that the human kidney cortex and neuronal beta(3) subunits were identical in nucleotide composition. Immunoblot analysis of rat kidney cortex and brain identified immunoreactive proteins in the 55 to 57 kD region, corresponding to the GABA(A) receptor beta(2) and beta(3) subunits. Immunohistochemistry revealed cytosolic and basolateral staining of the proximal convoluted and straight tubule. These results provide compelling evidence for the expression of the GABA(A) receptor beta(2) and beta(3) subunits in the kidney of multiple species and the localization of the beta(2)/beta(3) subunits to the renal proximal tubule.