Identification of the γ-aminobutyric acid receptor β₂ and β₃ subunits in rat, rabbit, and human kidneys

The properties and functions of γ-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 β₂ and β₃ subunits in the kidney. Reverse transcriptase products from RNA isolated from rat and rabbit kidney cortex and cerebellum and rabbit S₂ segments were amplified by use of PCR and GABA_A β₂ and β₃ subunit-specific primers. Sequencing of the kidney PCR products revealed that the rat kidney cortex and rat neuronal GABA_A receptor β₂ subunit were identical in nucleotide composition. The rabbit kidney and rabbit neuronal GABA_A receptor β₂ 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 β₃ subunits were 93% and 95% identical in nucleotide and amino acid composition, and rabbit kidney cortex and rabbit neuronal GABA_A receptor β₃ 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 β₃ 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 β₂ and β₃ 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 β₂ and β₃ subunits in the kidney of multiple species and the localization of the β₂/β₃ subunits to the renal proximal tubule.