Identification, Coassembly, and Activity of γ-Aminobutyric Acid Receptor Subunits in Renal Proximal Tubular Cells

Although the properties and functions of GABA_A receptors in the mammalian central nervous system have been well studied, the presence and significance of GABA_A receptors in non-neural tissues are less clear. The goal of this study was to examine the expression of GABA_A receptor α₁, α₂, α₄, α₅, β₁, γ₁, γ₂, and δ subunits in the kidney and to determine whether these subunits coassemble to form an active renal epithelial cell GABA_A receptor. Using reverse transcriptase products from RNA isolated from rat and rabbit kidney cortex and brain or cerebellum through polymerase chain reaction (PCR) and sequencing of the PCR products, we revealed that rat kidney cortex contained the α₁, α₅, β₁, γ₁, and γ₂ subunits and that they were similar to the neuronal subunits. Sequencing of the PCR products revealed that the rabbit kidney cortex contained the α₁ and γ₂ subunits and that they were similar to their neuronal counterparts. Immunoprecipitation and immunoblot studies using GABA_A receptor subunit-specific antibodies and detergent-solubilized rat kidney cortex membranes identified a GABA_A receptor complex containing α₅, β₁, and γ₁. Isolated rat renal proximal tubular cells exhibited GABA-mediated, picrotoxin-sensitive ³⁶Cl^- uptake. These studies demonstrate the presence of numerous GABA_A receptor subunits in the kidneys of two species, the assembly of the subunits into at least one novel receptor complex, and an active GABA_A receptor in renal proximal tubular cells.