Differential expression of γ-aminobutyric acid receptor A (GABAA) and effects of homocysteine

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Background:γ-Aminobutyric acid (GABA) is a known inhibitory neurotransmitter in the mammalian central nervous system, and homocysteine (Hcy) behaves as an antagonist for GABAA receptor. Although the properties and functions of GABAA receptors are well studied in mouse neural tissue, its presence and significance in non-neural tissue remains obscure. The aim of the present study was to examine the expression of GABAA receptor and its subunits in non-neural tissue.Methods:The mice were analyzed. The presence of GABAA receptor and its subunits was evaluated using Western blot and reverse transcription polymerase chain reaction.Results:We report that GABAA receptor protein is abundant in the renal medulla, cortex, heart, left ventricle, aorta and pancreas. Low levels of GABAA receptor protein were detected in the atria of the heart, right ventricle, lung and stomach. The mRNA protein expression of GABAA receptor subunit shows that α1, β1, β3 and γ1 subunits are present only in brain. The mRNA protein expression levels of GABAA receptor α2, α6, β2 and γ3 subunits were highly expressed in brain compared to other tested tissue, while GABAA receptor γ2 subunit was expressed only in brain and kidney. Treatment of microvascular endothelial cells with Hcy decreased GABAA receptor protein level, which was restored to its baseline level in the presence of GABAA receptor agonist, muscimol. The distribution of GABAA and GABAB receptors in wild type mice was determined and tissue-specific expression patterns were found showing that several receptor subtypes were also expressed in the central nervous system.Conclusions:Hcy, a GABAA agonist, was found to decrease GABAA expression levels. These data enlarge knowledge on distribution of GABA receptors and give novel ideas of the effects of Hcy on different organs.

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