Isolation of endogenous modulators for the GABAA and taurine receptors (original) (raw)
Related papers
British Journal of Pharmacology, 2003
The aim of this study was to find taurinergic compounds that do not interact with brain GABA ergic systems. 2 Washed synaptic membranes (SM) from whole rabbit brain were able to bind [ 3 H]muscimol. Saturation experiments of the binding of [ 3 H]GABA to GABA B receptors showed that SM possess two binding components; twice Triton X-100-treated SM contained 0.048 mmol endogenous taurine/ kg protein and bound [ 3 H]taurine in a saturable manner (K d ¼ 249.076.3 nm and B max ¼ 3.471.0 pmol mg À1 prot). 3 Among the 19 structural analogues of taurine, 6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine 1,1-dioxide (TAG), 2-aminoethylarsonic (AEA), 2-hydroxyethanesulfonic (ISE) and (7)cis-2aminocyclohexane sulfonic acids (CAHS) displaced [ 3 H]taurine binding (K i ¼ 0.13, 0.13, 13.5 and 4.0 mm, respectively). These analogues did not interact with GABA A and GABA B receptors and did not affect taurine-and GABA-uptake systems and GABA-transaminase activity. 4 3-Aminopropanesulfonic acid (OMO), b-alanine, pyridine-3-sulfonic acid, N,N,N-trimethyltaurine (TMT), 2-(guanidino)ethanesulfonic acid (GES), ethanolamine-O-sulphate, N,N-dimethyltaurine (DMT), taurine and (7)piperidine-3-sulfonic acid (PSA) inhibited [ 3 H]muscimol binding to GABA A receptors with different affinities (K i ¼ 0.013, 7.9, 24.6, 47.5, 52.0, 91.0, 47.5, 118.1 and 166.3 mm, respectively). Taurine, 2-aminoethylphosphonic acid, DMT, TMT and OMO inhibited the binding of [ 3 H]GABA to GABA B receptors with K i 's in the mm range (0.8, 3.5, 4.4, 11.3 and 5.0, respectively). GES inhibited taurine uptake (IC 50 ¼ 3.72 mm) and PSA GABA transaminase activity (IC 50 ¼ 103.0 mm). 5 In conclusion, AEA, TAG, ISE and CAHS fulfill the criteria for taurinergic agents.
Antagonism by antidepressants of muscarinic acetylcholine receptors of human brain
British Journal of Pharmacology, 1983
Twenty-two compounds classified as antidepressants, metabolites of antidepressants or putative antidepressants were assayed for their ability to antagonize the binding of (-)-[3H]-quinuclidinyl benzilate to muscarinic receptors in homogenates of human caudate nucleus. 2 Sixteen of these compounds were assayed for their ability to antagonize carbachol-stimulated cyclic guanosine 3',5'-monophosphate (cyclic GMP) synthesis by intact murine neuroblastoma cells (clone NlE-115). 3 Equilibrium dissociation constants (KDS) for these drugs and the muscarinic receptors of human brain spanned over 4 orders of magnitude, with the tertiary amine tricyclic antidepressant, amitriptyline (KD = 18 nM) being the most potent compound tested and trazodone (KD = 324 tMM) the least potent. 4 There was a significant correlation between the data for human and murine receptors and for eight compounds (imipramine, desipramine, maprotiline, mianserin, 3-chloro-2hydroxyimipramine, amoxapine, 2-hydroxyimipramine and iprindole). KD values measured by the two techniques were not significantly different.
Pharmacological characterization of GABAA receptors in taurine-fed mice
Journal of Biomedical Science, 2010
Background: Taurine is one of the most abundant free amino acids especially in excitable tissues, with wide physiological actions. Chronic supplementation of taurine in drinking water to mice increases brain excitability mainly through alterations in the inhibitory GABAergic system. These changes include elevated expression level of glutamic acid decarboxylase (GAD) and increased levels of GABA. Additionally we reported that GABA A receptors were down regulated with chronic administration of taurine. Here, we investigated pharmacologically the functional significance of decreased / or change in subunit composition of the GABA A receptors by determining the threshold for picrotoxin-induced seizures. Picrotoxin, an antagonist of GABA A receptors that blocks the channels while in the open state, binds within the pore of the channel between the β2 and β3 subunits. These are the same subunits to which GABA and presumably taurine binds. Methods: Two-month-old male FVB/NJ mice were subcutaneously injected with picrotoxin (5 mg kg-1) and observed for a) latency until seizures began, b) duration of seizures, and c) frequency of seizures. For taurine treatment, mice were either fed taurine in drinking water (0.05%) or injected (43 mg/kg) 15 min prior to picrotoxin injection. Results: We found that taurine-fed mice are resistant to picrotoxin-induced seizures when compared to agematched controls, as measured by increased latency to seizure, decreased occurrence of seizures and reduced mortality rate. In the picrotoxin-treated animals, latency and duration were significantly shorter than in taurinetreated animas. Injection of taurine 15 min before picrotoxin significantly delayed seizure onset, as did chronic administration of taurine in the diet. Further, taurine treatment significantly increased survival rates compared to the picrotoxin-treated mice. Conclusions: We suggest that the elevated threshold for picrotoxin-induced seizures in taurine-fed mice is due to the reduced binding sites available for picrotoxin binding due to the reduced expression of the beta subunits of the GABA A receptor. The delayed effects of picrotoxin after acute taurine injection may indicate that the two molecules are competing for the same binding site on the GABA A receptor. Thus, taurine-fed mice have a functional alteration in the GABAergic system. These include: increased GAD expression, increased GABA levels, and changes in subunit composition of the GABA A receptors. Such a finding is relevant in conditions where agonists of GABA A receptors, such as anesthetics, are administered.
Binding of muscimol and GABA in sub-fractions of a crude membrane fraction of rat brain
Biochemical Pharmacology, 1980
The binding of [3H]y-aminobutyric acid (L3H]GABA) 2nd [3H]muscimol to subcellular particles of brain, which occurs in the absence of added Na (i.e., "Na+-independent binding"), has been used to estimate synaptic . This binding appears to be most enriched in crude synaptic membrane fractions of brain (4-6), but all of the binding sites do not appear to be localized to synaptic membranes (e.g., 2,7,8). Recent studies have revealed further that the highest-affinity process for [3H]muscimol binding to subcellular particles of rat brain has a higher capacity than that of [3H]GABA (9-12). Herein, the binding ofthese ligands to sub-fractions of a crude membrane fraction of rat brain are compared.
Taurine Interaction with Neurotransmitter Receptors in the CNS: An Update
Neurochemical Research, 2005
Taurine appears to have multiple functions in the brain participating both in volume regulation and neurotransmission. In the latter context it may exert its actions by serving as an agonist at receptors of the GABAergic and glycinergic neurotransmitter systems. Its interaction with GABA A and GABA B receptors as well as with glycine receptors is reviewed and the physiological relevance of such interactions is evaluated. The question as to whether local extracellular concentrations of taurine are likely to reach the threshold level for the pertinent receptor populations cannot presently be answered satisfactorily. Hence more sophisticated analytical methods are warranted in order to obtain a definite answer to this important question.
Journal of Biological Chemistry, 1996
We have investigated the existence, molecular composition, and benzodiazepine binding properties of native cortical ␣ 1-␣ 3 ␥-aminobutyric acid A (GABA A) receptors using subunit-specific antibodies. The coexistence of ␣ 1 and ␣ 3 subunits in native GABA A receptors was demonstrated by immunoblot analysis of the anti-␣ 1-or anti-␣ 3-immunopurified receptors and by immunoprecipitation experiments of the [ 3 H]zolpidem binding activity. Furthermore, immunodepletion experiments indicated that the ␣ 1-␣ 3 GABA A receptors represented 54.7 ؎ 5.0 and 23.6 ؎ 3.3% of the ␣ 3 and ␣ 1 populations, respectively. Therefore, ␣ 1 and ␣ 3 subunits are associated in the same native GABA A receptor complex, but, on the other hand, these ␣ 1-␣ 3 GABA A receptors from the cortex constitute a large proportion of the total ␣ 3 population and a relatively minor component of the ␣ 1 population. The pharmacological analysis of the ␣ 1-or ␣ 3-immunopurified receptors demonstrated the presence of two different benzodiazepine binding sites in each receptor population with high (type I binding sites) and low (type II binding sites) affinities for zolpidem and Cl 218,872. These results indicate the existence of native GABA A receptors possessing both ␣ 1 and ␣ 3 subunits, with ␣ 1 and ␣ 3 subunits expressing their characteristic benzodiazepine pharmacology. The molecular characterization of the anti-␣ 1-anti-␣ 3 double-immunopurified receptors demonstrated the presence of stoichiometric amounts of ␣ 1 and ␣ 3 subunits, associated with  2/3 , and ␥ 2 subunits. The pharmacological analysis of ␣ 1-␣ 3 GABA A receptors demonstrated that, despite the fact that each ␣ subunit retained its benzodiazepine binding properties, the relative proportion between type I and II binding sites or between 51-and 59-61-kDa [ 3 H]Ro15-4513-photolabeled peptides was 70:30. Therefore, the ␣ 1 subunit is pharmacologically predominant over the ␣ 3 subunit. These results indicate the existence of active and nonactive ␣ subunits in the native ␣ 1-␣ 3 GABA A receptors from rat cortex. 1 The abbreviations used are: GABA A , ␥-aminobutyric acid A ; PBS, phosphate-buffered saline; FMZ, flumazenil; FNZ, flunitrazepam; mAb, monoclonal antibody; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid.