Differential expression of gamma-aminobutyric acid receptor A (GABA(A)) and effects of homocysteine.
BACKGROUND
gamma-Aminobutyric acid (GABA) is a known inhibitory neurotransmitter in the mammalian central nervous system, and homocysteine (Hcy) behaves as an antagonist for GABA(A) receptor. Although the properties and functions of GABA(A) 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 GABA(A) receptor and its subunits in non-neural tissue.


METHODS
The mice were analyzed. The presence of GABA(A) receptor and its subunits was evaluated using Western blot and reverse transcription polymerase chain reaction.


RESULTS
We report that GABA(A) receptor protein is abundant in the renal medulla, cortex, heart, left ventricle, aorta and pancreas. Low levels of GABA(A) receptor protein were detected in the atria of the heart, right ventricle, lung and stomach. The mRNA protein expression of GABA(A) receptor subunit shows that alpha1, beta1, beta3 and gamma1 subunits are present only in brain. The mRNA protein expression levels of GABA(A) receptor alpha2, alpha6, beta2 and gamma3 subunits were highly expressed in brain compared to other tested tissue, while GABA(A) receptor gamma2 subunit was expressed only in brain and kidney. Treatment of microvascular endothelial cells with Hcy decreased GABA(A) receptor protein level, which was restored to its baseline level in the presence of GABA(A) receptor agonist, muscimol. The distribution of GABA(A) and GABA(B) 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 GABA(A) agonist, was found to decrease GABA(A) expression levels. These data enlarge knowledge on distribution of GABA receptors and give novel ideas of the effects of Hcy on different organs.
Tyagi
Neetu
N
Department of Physiology and Biophysics, School of Medicine, University of Louisville, Louisville, KY 40202, USA.
Lominadze
David
D
Gillespie
William
W
Moshal
Karni S
KS
Sen
Utpal
U
Rosenberger
Dorothea S
DS
Steed
Mesia
M
Tyagi
Suresh C
SC
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D017931:DNA Primers; D006710:Homocysteine / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000235:genetics; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D017931:DNA Primers; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D006710:Homocysteine