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Gerbier R, Jockers R. GTPγS Binding Assay for Melatonin Receptors in Mouse Brain Tissue. Methods Mol Biol 2022; 2550:163-169. [PMID: 36180689 DOI: 10.1007/978-1-0716-2593-4_20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The [35S]GTPγS assay is a method that measures the level of G protein activation by determining the binding of [35S]GTPγS, a non-hydrolyzable and radioactively labeled GTP analog, to Gα subunit of heterotrimeric G protein upon activation of G protein-coupled receptors (GPCR). The power of this assay lies in the fact that it measures an early event of GPCR signaling in cells expressing recombinant receptors and cells and tissues expressing endogenous receptors. The present protocol describes a sensitive method for studying G protein activation by melatonin receptors MT1 and MT2, in membranes prepared from mouse brain. Immunoprecipitation of [35S]GTPγS-labeled G proteins with Gα subunit specific antibodies (Gi, Gq, etc.) allows to determine the activation of specific G proteins. The assay can be easily applied to other tissues.
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Affiliation(s)
- Romain Gerbier
- Université de Paris, Institut Cochin, INSERM, CNRS, Paris, France
| | - Ralf Jockers
- Université de Paris, Institut Cochin, INSERM, CNRS, Paris, France.
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Odagaki Y, Kinoshita M, Meana JJ, Callado LF, García-Sevilla JA. 5-HT 2A receptor-mediated Gα q/11 activation in psychiatric disorders: A postmortem study. World J Biol Psychiatry 2021; 22:505-515. [PMID: 33084439 DOI: 10.1080/15622975.2020.1839967] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
OBJECTIVES Serotonin-2A (5-HT2A) receptors play an important role in the regulation of many brain functions that are disturbed in patients with such psychiatric diseases as mood disorders and schizophrenia. The objective of this study was to evaluate 5-HT2A receptor-mediated signalling pathway through Gαq/11 activation in psychiatric patients by using post-mortem brain samples. METHODS Functional activation of Gαq/11 proteins coupled to 5-HT2A receptors was determined by means of [35S]GTPγS binding/immunoprecipitation assay in post-mortem prefrontal cortex of psychiatric patients diagnosed as bipolar disorder (BP), major depressive disorder (MDD), and schizophrenia, and individually matched controls. The effects of antipsychotic treatment as well as suicide were also analysed. RESULTS There was no significant difference in maximum percent increase (%Emax) or slope factor among the four groups. The negative logarithm of concentration eliciting the half-maximal effect (pEC50) was significantly reduced in BP and schizophrenia patients as compared to controls. These alterations were attributable to antipsychotic medication. The pEC50 values in 'non-suicide' group of schizophrenia, but not in 'suicide' group, were significantly reduced as compared with controls. CONCLUSIONS Altered 5-HT2A receptor-mediated signalling pathway through Gαq/11 proteins in prefrontal cortex might be apparently involved in pathophysiology and pharmacotherapy of BP and schizophrenia. In schizophrenic patients, these alterations as a result of successful treatment with antipsychotic agents may help in prevention of suicidal behaviour.
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Affiliation(s)
- Yuji Odagaki
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Iruma-gun, Saitama, Japan
| | - Masakazu Kinoshita
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Iruma-gun, Saitama, Japan
| | - José Javier Meana
- Department of Pharmacology, University of the Basque Country, Leioa, Spain.,Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Leioa, Spain
| | - Luis F Callado
- Department of Pharmacology, University of the Basque Country, Leioa, Spain.,Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Leioa, Spain
| | - Jesús A García-Sevilla
- Laboratory of Neuropharmacology, IUNICS/IdISPa, University of the Balearic Islands (UIB), Palma de Mallorca, Spain
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Functional approaches to the study of G-protein-coupled receptors in postmortem brain tissue: [ 35S]GTPγS binding assays combined with immunoprecipitation. Pharmacol Rep 2021; 73:1079-1095. [PMID: 33876404 DOI: 10.1007/s43440-021-00253-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 03/16/2021] [Accepted: 03/19/2021] [Indexed: 10/21/2022]
Abstract
G-protein-coupled receptors (GPCRs) have an enormous biochemical importance as they bind to diverse extracellular ligands and regulate a variety of physiological and pathological responses. G-protein activation measures the functional consequence of receptor occupancy at one of the earliest receptor-mediated events. Receptor coupling to G-proteins promotes the GDP/GTP exchange on Gα subunits. Thus, modulation of the binding of the poorly hydrolysable GTP analog [35S]GTPγS to the Gα-protein subunit can be used as a functional approach to quantify GPCR interaction with agonist, antagonist or inverse agonist drugs. In order to determine receptor-mediated selective activation of the different Gα-proteins, [35S]GTPγS binding assays combined with immunodetection by specific antibodies have been developed and applied to physiological and pathological brain conditions. Currently, immunoprecipitation with magnetic beads and scintillation proximity assays are the most habitual techniques for this purpose. The present review summarizes the different procedures, advantages and limitations of the [35S]GTPγS binding assays combined with selective Gα-protein sequestration methods. Experience of functional coupling of several GPCRs to different Gα-proteins and recommendations for optimal performance in brain membranes are described. One of the biggest opportunities opened by these techniques is that they enable evaluation of biased agonism in the native tissue, which results in high interest in drug discovery. The available results derived from application of these functional methodologies to study GPCR dysfunctions in neuro-psychiatric disorders are also described. In conclusion, [35S]GTPγS binding combined with antibody-mediated immunodetection represents an useful method to separately evaluate the functional activity of drugs acting on GPCRs over each Gα-protein subtype.
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5-HT 2A receptor- and M 1 muscarinic acetylcholine receptor-mediated activation of Gα q/11 in postmortem dorsolateral prefrontal cortex of opiate addicts. Pharmacol Rep 2021; 73:1155-1163. [PMID: 33835465 DOI: 10.1007/s43440-021-00248-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2021] [Revised: 03/05/2021] [Accepted: 03/11/2021] [Indexed: 10/21/2022]
Abstract
BACKGROUND Chronic exposure to opiates causes the development of tolerance and physical dependence as well as persistent brain neuroplasticity. Despite a wealth of postmortem human studies for opiate addicts, little direct information regarding the functional status of serotonergic and cholinergic receptor-mediated signaling pathways in the human brain of opiate addicts is yet available. METHODS Functional activation of Gαq/11 proteins coupled to 5-HT2A and M1 type muscarinic acetylcholine receptor (mAChR) was assessed by using the method named [35S]GTPγS binding/immunoprecipitation in frontal cortical membrane preparations from postmortem human brains obtained from opiate addicts and matched controls. RESULTS Concentration-response curves for 5-HT and carbachol in individual subjects were analyzed according to a nonlinear regression model, which generated the values of maximum percent increase (%Emax), negative logarithm of the half-maximal effect (pEC50) and slope factor. As for 5-HT2A receptor-mediated Gαq/11 activation, the %Emax values were reduced significantly and the pEC50 values were decreased significantly in opiate addicts as compared to the control group. Regarding carbachol-induced Gαq/11 activation, no significant difference in %Emax or pEC50 values was detected between the both groups, whereas the slope factor was increased significantly in opiate addicts as compared to the control group. CONCLUSION Our data demonstrate that the signaling pathways mediated by Gαq/11 proteins coupled with 5-HT2A receptors and M1 mAChRs in prefrontal cortex are functionally altered in opiate addicts in comparison with control subjects. These alterations may underpin some aspects of addictive behavior to opiate as well as neuropsychological consequences or comorbid mental disorders associated with opioid use.
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Odagaki Y, Kinoshita M, Ota T. Dopamine-induced functional activation of Gα q mediated by dopamine D 1-like receptor in rat cerebral cortical membranes. J Recept Signal Transduct Res 2019; 39:9-17. [PMID: 31223051 DOI: 10.1080/10799893.2018.1562470] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Although multiple roles of dopamine through D1-like (D1 and D5) and D2-like (D2, D3, and D4) receptors are initiated primarily through stimulation or inhibition of adenylyl cyclase via Gs/olf or Gi/o, respectively, there have been many reports indicating diverse signaling mechanisms that involve alternative G protein coupling. In this study, dopamine-induced Gαq activation in rat brain membranes was investigated. Agonist-induced Gαq activation was assessed by increase in guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPγS) binding to Gαq determined by [35S]GTPγS binding/immunoprecipitation assay in rat brain membranes. Dopamine-stimulated Gαq functionality was highest in cortex as compared to hippocampus or striatum. In cerebral cortical membranes, this effect was mimicked by benzazepine derivatives with agonist properties at dopamine D1-like receptors, that is, SKF83959, SKF83822, R(+)-SKF81297, R(+)-SKF38393, and SKF82958, but not by the compounds with dopamine D2-like receptor agonist properties except for aripiprazole. Against expectation, stimulatory effects were also induced by SKF83566, R(+)-SCH23390, and pergolide. The pharmacological profiling by using a series of antagonists indicated that dopamine-induced response was mediated through dopamine D1-like receptor, which was distinct from the receptor involved in 5-HT-induced response (5-HT2A receptor). Conversely, the responses induced by SKF83566, R(+)-SCH23390, and pergolide were most likely mediated by 5-HT2A receptor, but not by dopamine D1-like receptor. Caution should be paid when interpreting the experimental data, especially in behavioral pharmacological research, in which SKF83566 or R(+)-SCH23390 is used as a standard selective dopamine D1-like receptor antagonist. Also, possible clinical implications of the agonistic effects of pergolide on 5-HT2A receptor has been mentioned.
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Affiliation(s)
- Yuji Odagaki
- a Department of Psychiatry, Faculty of Medicine , Saitama Medical University , Saitama , Japan
| | - Masakazu Kinoshita
- a Department of Psychiatry, Faculty of Medicine , Saitama Medical University , Saitama , Japan
| | - Toshio Ota
- a Department of Psychiatry, Faculty of Medicine , Saitama Medical University , Saitama , Japan
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Odagaki Y, Kinoshita M, Ota T. Functional activation of Gα q/11 protein via α 1 -adrenoceptor in rat cerebral cortical membranes. Clin Exp Pharmacol Physiol 2019; 46:567-574. [PMID: 30869808 DOI: 10.1111/1440-1681.13084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2019] [Revised: 02/21/2019] [Accepted: 03/09/2019] [Indexed: 11/26/2022]
Abstract
Although it is recognized that α1 -adrenoceptors are coupled to diverse intracellular signalling pathways, its primary transduction mechanisms are evoked by activating phospholipase C in the cell membrane through Gαq/11 , resulting in production of inositol 1,4,5-trisphosphate and diacylglycerol. However, there have been few studies that indicate directly the involvement of Gαq/11 proteins in this signalling pathway in the central nervous system. In the current study, we tried to pharmacologically characterize (-)-adrenaline-stimulated [35 S]GTPγS binding to Gαq/11 in rat brain membranes. Functional activation of Gαq/11 coupled to α1 -adrenoceptor was investigated by using [35 S]GTPγS binding/immunoprecipitation assay in the membranes prepared from rat cerebral cortex, hippocampus, and striatum. The specific [35 S]GTPγS binding to Gαq/11 was stimulated by (-)-adrenaline in a concentration-dependent and saturable manner in rat cerebral cortical membranes. In hippocampal or striatal membranes, the stimulatory effects of (-)-adrenaline were scarce. The effect of (-)-adrenaline was potently inhibited by prazosin, a potent and selective α1 -adrenoceptor antagonist, but not by yohimbine, a selective α2 -adrenoceptor antagonist. The response was mimicked by cirazoline, but not by R(-)-phenylephrine. Although oxymetazoline also stimulated the specific [35 S]GTPγS binding to Gαq/11 as an apparent "super-agonist", detailed pharmacological characterization revealed that its agonistic properties in this experimental system were derived from off-target effects on 5-HT2A receptors, but not via α1 -adrenoceptors. In conclusion, functional coupling of α1 -adrenoceptors to Gαq/11 proteins are detectable in rat brain membranes by means of [35 S]GTPγS binding/immunoprecipitation assay. It is necessary to interpret the experimental data with caution when oxymetazoline is included as an agonist at α1 -adrenoceptors.
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Affiliation(s)
- Yuji Odagaki
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Moroyama-machi, Iruma-gun, Saitama 350-0495, Japan
| | - Masakazu Kinoshita
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Moroyama-machi, Iruma-gun, Saitama 350-0495, Japan
| | - Toshio Ota
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Moroyama-machi, Iruma-gun, Saitama 350-0495, Japan
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Odagaki Y. Guanosine-5′-O-(3-[35S]thio)triphosphate ([35S]GTPγS) Binding/Immunoprecipitation Assay Using Magnetic Beads Coated with Anti-Gα Antibody in Mammalian Brain Membranes. CO-IMMUNOPRECIPITATION METHODS FOR BRAIN TISSUE 2019. [DOI: 10.1007/978-1-4939-8985-0_8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Odagaki Y, Kinoshita M, Ota T, Javier Meana J, Callado LF, García-Sevilla JA. Functional activation of Gαq coupled to 5-HT2A receptor and M1 muscarinic acetylcholine receptor in postmortem human cortical membranes. J Neural Transm (Vienna) 2017; 124:1123-1133. [DOI: 10.1007/s00702-017-1749-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 06/20/2017] [Indexed: 11/30/2022]
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Odagaki Y, Kinoshita M, Ota T. Comparative analysis of pharmacological properties of xanomeline and N-desmethylclozapine in rat brain membranes. J Psychopharmacol 2016; 30:896-912. [PMID: 27464743 DOI: 10.1177/0269881116658989] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
BACKGROUND 3(3-Hexyloxy-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine (xanomeline) and N-desmethylclozapine are of special interest as promising antipsychotics with better efficacy, especially for negative symptoms and/or cognitive/affective impairment. METHODS The guanosine-5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPγS) binding experiments were performed using (1) conventional filtration technique, (2) antibody-capture scintillation proximity assay, and (3) immunoprecipitation method, in brain membranes prepared from rat cerebral cortex, hippocampus, and striatum. RESULTS Xanomeline had agonistic activity at the M1 muscarinic acetylcholine receptor (mAChR) in all brain regions, as well as at the 5-HT1A receptor in the cerebral cortex and hippocampus. On the other hand, N-desmethylclozapine exhibited slight agonistic effects on the M1 mAChR, and agonistic properties at the 5-HT1A receptor in the cerebral cortex and hippocampus. This compound also behaved as an agonist at the δ-opioid receptor in the cerebral cortex and striatum. In addition, the stimulatory effects of N-desmethylclozapine on [(35)S]GTPγS binding to Gαi/o were partially mediated through mAChRs (most likely M4 mAChR subtype), at least in striatum. CONCLUSIONS The agonistic effects on the mAChRs (particularly M1 subtype, and also probably M4 subtype), the 5-HT1A receptor and the δ-opioid receptor expressed in native brain tissues, some of which are common to both compounds and others specific to either, likely shape the unique beneficial effectiveness of both compounds in the treatment for schizophrenic patients. These characteristics provide us with a clue to develop newer antipsychotics, beyond the framework of dopamine D2 receptor antagonism, that are effective not only on positive symptoms but also on negative symptoms and/or cognitive/affective impairment.
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Affiliation(s)
- Yuji Odagaki
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Masakazu Kinoshita
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Toshio Ota
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Saitama, Japan
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Odagaki Y, Kinoshita M, Ota T, Javier Meana J, Callado LF, García-Sevilla JA. Adenosine A1( )receptors are selectively coupled to Gα(i-3) in postmortem human brain cortex: Guanosine-5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPγS) binding/immunoprecipitation study. Eur J Pharmacol 2015. [PMID: 26213104 DOI: 10.1016/j.ejphar.2015.07.049] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
By means of guanosine-5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPγS) binding assay combined with immunoprecipitation using anti-Gα subunit antibody, we recently reported 5-HT2A receptor- and M1 muscarinic acetylcholine receptor-mediated Gαq activation in rat cerebral cortical membranes (Odagaki et al., 2014). In the present study, this method has been applied to postmortem human brains, with focusing on adenosine receptor-mediated G-protein activation. In the exploratory experiments using a series of agonists and the antibodies specific to each Gα subtypes in the presence of low (10 nM) or high (50 μM) concentration of GDP, the most prominent increases in specific [(35)S]GTPγS binding in the membranes prepared from human prefrontal cortex were obtained for the combinations of adenosine (1mM)/anti-Gαi-3 in the presence of 50 μM GDP as well as 5-HT (100 μM)/anti-Gαq and carbachol (1mM)/anti-Gαq in the presence of 10nM GDP. Adenosine-induced activation of Gαi-3 emerged only when GDP concentrations were increased higher than 10 μM, and the following experiments were performed in the presence of 300 μM GDP. Adenosine increased specific [(35)S]GTPγS binding to Gαi-3 in a concentration-dependent manner to 251.4% of the basal unstimulated binding, with an EC50 of 1.77 μM. The involvement of adenosine A1 receptor was verified by the experiments using selective agonists and antagonists at adenosine A1 or A3 receptor. Among the α subunits of Gi/o class (Gαi-1, Gαi-2, Gαi-3, and Gαo.), only Gαi-3 was activated by 1mM adenosine, indicating that human brain adenosine A1 receptor is coupled preferentially, if not exclusively, to Gαi-3.
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Affiliation(s)
- Yuji Odagaki
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, 38 Morohongo, Iruma-gun, Moroyama-machi, Saitama 350-0495, Japan.
| | - Masakazu Kinoshita
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, 38 Morohongo, Iruma-gun, Moroyama-machi, Saitama 350-0495, Japan
| | - Toshio Ota
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, 38 Morohongo, Iruma-gun, Moroyama-machi, Saitama 350-0495, Japan
| | - J Javier Meana
- Department of Pharmacology, University of the Basque Country, UPV/EHU, E-48940 Leioa, Bizkaia, and Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Spain
| | - Luis F Callado
- Department of Pharmacology, University of the Basque Country, UPV/EHU, E-48940 Leioa, Bizkaia, and Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Spain
| | - Jesús A García-Sevilla
- Laboratory of Neuropharmacology, IUNICS/IdISPa, University of the Balearic Islands (UIB), and Redes Temáticas de Investigación Cooperativa en Salud-Red de Trastornos Adictivos (RETICS-RTA), Spain
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Giulietti M, Vivenzio V, Piva F, Principato G, Bellantuono C, Nardi B. How much do we know about the coupling of G-proteins to serotonin receptors? Mol Brain 2014; 7:49. [PMID: 25011628 PMCID: PMC4105882 DOI: 10.1186/s13041-014-0049-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 06/27/2014] [Indexed: 11/30/2022] Open
Abstract
Serotonin receptors are G-protein-coupled receptors (GPCRs) involved in a variety of psychiatric disorders. G-proteins, heterotrimeric complexes that couple to multiple receptors, are activated when their receptor is bound by the appropriate ligand. Activation triggers a cascade of further signalling events that ultimately result in cell function changes. Each of the several known G-protein types can activate multiple pathways. Interestingly, since several G-proteins can couple to the same serotonin receptor type, receptor activation can result in induction of different pathways. To reach a better understanding of the role, interactions and expression of G-proteins a literature search was performed in order to list all the known heterotrimeric combinations and serotonin receptor complexes. Public databases were analysed to collect transcript and protein expression data relating to G-proteins in neural tissues. Only a very small number of heterotrimeric combinations and G-protein-receptor complexes out of the possible thousands suggested by expression data analysis have been examined experimentally. In addition this has mostly been obtained using insect, hamster, rat and, to a lesser extent, human cell lines. Besides highlighting which interactions have not been explored, our findings suggest additional possible interactions that should be examined based on our expression data analysis.
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Affiliation(s)
| | | | - Francesco Piva
- Department of Specialized Clinical Sciences and Odontostomatology, Polytechnic University of Marche, Ancona, Italy.
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Odagaki Y, Kinoshita M, Toyoshima R. Functional activation of G-proteins coupled with muscarinic acetylcholine receptors in rat brain membranes. J Pharmacol Sci 2014; 125:157-68. [PMID: 24849282 DOI: 10.1254/jphs.14020fp] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
The functional activation of Gi/o proteins coupled to muscarinic acetylcholine receptors (mAChRs) was investigated with the conventional guanosine-5'-O-(3-[(35)S]thio) triphosphate ([(35)S]GTPγS) binding assay in rat brain membranes. The most efficacious stimulation elicited by acetylcholine or carbachol (CCh) was obtained in striatal membranes. The pharmacological properties of mAChR-mediated [(35)S]GTPγS binding determined with a series of muscarinic agonists and antagonists were almost identical among the three brain regions investigated, i.e., cerebral cortex, hippocampus, and striatum, except for the apparent partial agonist effects of (αR)-α-cyclopentyl-α-hydroxy-N-[1-(4-methyl-3-pentenyl)-4-piperidinyl]benzeneacetamide fumarate (J 104129) observed only in the hippocampus, but not in the other two regions. Among the muscarinic toxins investigated, only MT3 attenuated CCh-stimulated [(35)S] GTPγS binding. The highly selective allosteric potentiator at the M4 mAChR subtype, 3-amino-N-[(4-chlorophenyl)methyl]-4,6-dimethylthieno[2,3-b]pyridine-2-carboxamide (VU 10010), shifted the concentration-response curve for CCh leftwards as well as upwards. On the other hand, neither thiochrome nor brucine N-oxide was effective. The increases induced by CCh and 5-HT were essentially additive, though not completely, indicating that the mAChRs and 5-HT1A receptors were coupled independently to distinct pools of Gi/o proteins. Collectively, all of the data suggest that functional activation of Gi/o proteins coupled to mAChRs, especially the M4 subtype, is detectable by means of CCh-stimulated [(35)S]GTPγS binding assay in rat discrete brain regions.
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Affiliation(s)
- Yuji Odagaki
- Department of Psychiatry, Faculty of Medicine, Saitama Medical University, Japan
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