Characteristic expressions of GABA receptors and GABA producing/transporting molecules in rat kidney.

Kozue Takano,Hironobu Sanada,Midori Sasaki Yatabe,Yu Suzuki,Tsuyoshi Watanabe,Junko Kimura,Junichi Yatabe,Asami Abe

doi:10.1371/journal.pone.0105835

Abstract

Gamma-aminobutyric acid (GABA) is an important neurotransmitter, but recent reports have revealed the expression of GABAergic components in peripheral, non-neural tissues. GABA administration induces natriuresis and lowers blood pressure, suggesting renal GABA targets. However, systematic evaluation of renal GABAergic components has not been reported. In this study, kidney cortices of Wistar-Kyoto rats (WKY) were used to assay for messenger RNAs of GABA-related molecules using RT-PCR. In WKY kidney cortex, GABAA receptor subunits, α1, β3, δ, ε and π, in addition to both types of GABAB receptors, R1 and R2, and GABAC receptor ρ1 and ρ2 subunit mRNAs were detected. Kidney cortex also expressed mRNAs of glutamate decarboxylase (GAD) 65, GAD67, 4-aminobutyrate aminotransferase and GABA transporter, GAT2. Western blot and/or immunohistochemistry were performed for those molecules detected by RT-PCR. By immunofluorescent observation, co-staining of α1, β3, and π subunits was observed mainly on the apical side of cortical tubules, and immunoblot of kidney protein precipitated with π subunit antibody revealed α1 and β3 subunit co-assembly. This is the first report of GABAA receptor π subunit in the kidney. In summary, unique set of GABA receptor subunits and subtypes were found in rat kidney cortex. As GABA producing enzymes, transporters and degrading enzyme were also detected, a possible existence of local renal GABAergic system with an autocrine/paracrine mechanism is suggested.

Highlights

Gamma-aminobutyric acid (GABA) acts as a major inhibitory neurotransmitter in the central nervous system
Expressions of GABAA receptor a1, b3, d, e and p subunits were detected in rat kidney cortex
Kidneys for GABAA p subunit, we found no significant difference in the expression level GABAA p subunit in the kidney cortex of four groups of rats, Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) with and without salt loading on the protein level

Summary

Introduction

Gamma-aminobutyric acid (GABA) acts as a major inhibitory neurotransmitter in the central nervous system. Released GABA acts on two general classes of its receptors, GABAA/GABAC and GABAB. GABAA and GABAC receptors are ligand-gated chloride channels composed of a combination of various subunits as pentamers. The unique sensitivity of GABAA receptor to its agonist such as benzodiazepines is known to depend on the combination of subunits including a, b, c, d, e, p, and h [1,2]. GABAB receptor controls neuronal activity via activation of K+ channels, inhibition of Ca2+ channels, or both. Similar to the GABAA receptor-mediated increase in the conductance of Cl2, the activation of K+ channels from the GABAB signaling induces hyperpolarization of the cell membrane, which produces chronic stabilization of neuronal activity [3]. GABA secreted from neurons subsequently undergoes re-uptake via GABA transporters (GAT) and is metabolized by the GABA degrading enzyme, 4aminobutyrate aminotransferase (ABAT) [4]

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