Biomaterial Database

GABAA and GABAB receptor-mediated effects in guinea-pig ileum. 1983

A Giotti, and S Luzzi, and S Spagnesi, and L Zilletti

1 The effects of gamma-aminobutyric acid (GABA) and related substances were examined in guinea-pig ileum longitudinal muscle.2 GABA at doses ranging from 10(-7) M to 3 x 10(-6) M elicited a relaxation while at higher doses (3 x 10(-6) M - 10(-4) M), as previously described, it caused a contraction followed by relaxation.3 GABA-induced relaxation was bicuculline-insensitive, was mimicked by (-)-baclofen but not by homotaurine and muscimol. The effect of baclofen was stereospecific. GABA- and (-)-baclofen-induced relaxations were dose-dependent and their ED(50) values were similar. A specific cross-desensitization occurred between GABA and (-)-baclofen.4 The bicuculline-insensitive relaxation induced by GABA and (-)-baclofen was prevented by tetrodotoxin and hyoscine but not by phentolamine plus propranolol, naloxone or theophylline.5 In preparations in which the muscle tone was raised by histamine or prostaglandin F(2alpha), GABA and (-)-baclofen induced relaxation to the same extent as before increasing the tone. If the tone was raised by DMPP, a greater bicuculline-insensitive relaxation occurred.6 Contraction caused by GABA was bicuculline-sensitive and was mimicked by homotaurine and muscimol. Contraction was dose-dependent and muscimol was about three times more potent than GABA or homotaurine. A specific cross-desensitization occurred between the contractile effects of GABA and those of homotaurine or muscimol.7 Bicuculline competitively antagonized the contractile effects of GABA, homotaurine and muscimol and gave closely similar pA(2) values. The slope of the Schild plot for the above drugs was near 1, confirming the competitive nature of the antagonism.8 The bicuculline-sensitive contraction induced by GABA, homotaurine and muscimol was abolished by tetrodotoxin and was non-competitively antagonized by hyoscine, while it was unaffected by hexamethonium, mepyramine and methysergide.9 It is concluded that two receptors mediate the GABA effects in guinea-pig ileum: a bicuculline-sensitive GABA(A) receptor, which elicits contraction through an excitatory action on cholinergic post-ganglionic neurones; and a bicuculline-insensitive GABA(B) receptor which causes relaxation through an inhibitory presynaptic action on cholinergic post-ganglionic neurones. We confirm that GABA, homotaurine and muscimol are GABA(A) agonists, while GABA and (-)-baclofen are GABA(B) agonists.

UI	MeSH Term	Description	Entries
D007082	Ileum	The distal and narrowest portion of the SMALL INTESTINE, between the JEJUNUM and the ILEOCECAL VALVE of the LARGE INTESTINE.
D008297	Male		Males
D009118	Muscimol	A neurotoxic isoxazole isolated from species of AMANITA. It is obtained by decarboxylation of IBOTENIC ACID. Muscimol is a potent agonist of GABA-A RECEPTORS and is used mainly as an experimental tool in animal and tissue studies.	Agarin,Pantherine
D009119	Muscle Contraction	A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.	Inotropism,Muscular Contraction,Contraction, Muscle,Contraction, Muscular,Contractions, Muscle,Contractions, Muscular,Inotropisms,Muscle Contractions,Muscular Contractions
D009130	Muscle, Smooth	Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. (From Stedman, 25th ed)	Muscle, Involuntary,Smooth Muscle,Involuntary Muscle,Involuntary Muscles,Muscles, Involuntary,Muscles, Smooth,Smooth Muscles
D011956	Receptors, Cell Surface	Cell surface proteins that bind signalling molecules external to the cell with high affinity and convert this extracellular event into one or more intracellular signals that alter the behavior of the target cell (From Alberts, Molecular Biology of the Cell, 2nd ed, pp693-5). Cell surface receptors, unlike enzymes, do not chemically alter their ligands.	Cell Surface Receptor,Cell Surface Receptors,Hormone Receptors, Cell Surface,Receptors, Endogenous Substances,Cell Surface Hormone Receptors,Endogenous Substances Receptors,Receptor, Cell Surface,Surface Receptor, Cell
D011963	Receptors, GABA-A	Cell surface proteins which bind GAMMA-AMINOBUTYRIC ACID and contain an integral membrane chloride channel. Each receptor is assembled as a pentamer from a pool of at least 19 different possible subunits. The receptors belong to a superfamily that share a common CYSTEINE loop.	Benzodiazepine-Gaba Receptors,GABA-A Receptors,Receptors, Benzodiazepine,Receptors, Benzodiazepine-GABA,Receptors, Diazepam,Receptors, GABA-Benzodiazepine,Receptors, Muscimol,Benzodiazepine Receptor,Benzodiazepine Receptors,Benzodiazepine-GABA Receptor,Diazepam Receptor,Diazepam Receptors,GABA(A) Receptor,GABA-A Receptor,GABA-A Receptor alpha Subunit,GABA-A Receptor beta Subunit,GABA-A Receptor delta Subunit,GABA-A Receptor epsilon Subunit,GABA-A Receptor gamma Subunit,GABA-A Receptor rho Subunit,GABA-Benzodiazepine Receptor,GABA-Benzodiazepine Receptors,Muscimol Receptor,Muscimol Receptors,delta Subunit, GABA-A Receptor,epsilon Subunit, GABA-A Receptor,gamma-Aminobutyric Acid Subtype A Receptors,Benzodiazepine GABA Receptor,Benzodiazepine Gaba Receptors,GABA A Receptor,GABA A Receptor alpha Subunit,GABA A Receptor beta Subunit,GABA A Receptor delta Subunit,GABA A Receptor epsilon Subunit,GABA A Receptor gamma Subunit,GABA A Receptor rho Subunit,GABA A Receptors,GABA Benzodiazepine Receptor,GABA Benzodiazepine Receptors,Receptor, Benzodiazepine,Receptor, Benzodiazepine-GABA,Receptor, Diazepam,Receptor, GABA-A,Receptor, GABA-Benzodiazepine,Receptor, Muscimol,Receptors, Benzodiazepine GABA,Receptors, GABA A,Receptors, GABA Benzodiazepine,delta Subunit, GABA A Receptor,epsilon Subunit, GABA A Receptor,gamma Aminobutyric Acid Subtype A Receptors
D005680	gamma-Aminobutyric Acid	The most common inhibitory neurotransmitter in the central nervous system.	4-Aminobutyric Acid,GABA,4-Aminobutanoic Acid,Aminalon,Aminalone,Gammalon,Lithium GABA,gamma-Aminobutyric Acid, Calcium Salt (2:1),gamma-Aminobutyric Acid, Hydrochloride,gamma-Aminobutyric Acid, Monolithium Salt,gamma-Aminobutyric Acid, Monosodium Salt,gamma-Aminobutyric Acid, Zinc Salt (2:1),4 Aminobutanoic Acid,4 Aminobutyric Acid,Acid, Hydrochloride gamma-Aminobutyric,GABA, Lithium,Hydrochloride gamma-Aminobutyric Acid,gamma Aminobutyric Acid,gamma Aminobutyric Acid, Hydrochloride,gamma Aminobutyric Acid, Monolithium Salt,gamma Aminobutyric Acid, Monosodium Salt
D006168	Guinea Pigs	A common name used for the genus Cavia. The most common species is Cavia porcellus which is the domesticated guinea pig used for pets and biomedical research.	Cavia,Cavia porcellus,Guinea Pig,Pig, Guinea,Pigs, Guinea
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia