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M2 Receptors (m2 + receptor)
Selected AbstractsRegulation of bladder muscarinic receptor subtypes by experimental pathologiesAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 3 2006M. R. Ruggieri Sr Summary 1 The M3 muscarinic receptor subtype is widely accepted as the receptor on smooth muscle cells that mediates cholinergic contraction of the normal urinary bladder and other smooth muscle tissues, however, we have found that the M2 receptor participates in contraction under certain abnormal conditions. The aim of this study was to determine the effects of various experimental pathologies on the muscarinic receptor subtype mediating urinary bladder contraction. 2 Experimental pathologies resulting in bladder hypertrophy (denervation and outlet obstruction) result in an up-regulation of bladder M2 receptors and a change in the receptor subtype mediating contraction from M3 towards M2. Preventing the denervation-induced bladder hypertrophy by urinary diversion prevents this shift in contractile phenotype indicating that hypertrophy is responsible as opposed to denervation per se. 3 The hypertrophy-induced increase in M2 receptor density and contractile response is accompanied by an increase in the tissue concentrations of mRNA coding for the M2 receptor subtype, however, M3 receptor protein density does not correlate with changes in M3 receptor tissue mRNA concentrations across different experimental pathologies. 4 This shift in contractile phenotype from M3 towards M2 subtype is also observed in aged male Sprague,Dawley rats but not females or either sex of the Fisher344 strain of rats. 5 Four repeated, sequential agonist concentration response curves also cause this shift in contractile phenotype in normal rat bladder strips in vitro, as evidenced by a decrease in the affinity of the M3 selective antagonist p -fluoro-hexahydro-sila-diphenidol (p -F-HHSiD). 6 A similar decrease in the contractile affinity of M3 selective antagonists (darifenacin and p -F-HHSiD) is also observed in bladder specimens from patients with neurogenic bladder as well as certain organ transplant donors. 7 It is concluded that although the M3 receptor subtype predominately mediates contraction under normal circumstances, the M2 receptor subtype can take over a contractile role when the M3 subtype becomes inactivated by, for example, repeated agonist exposures or bladder hypertrophy. This finding has substantial implications for the clinical treatment of abnormal bladder contractions. [source] Negative cross-talk between presynaptic adenosine and acetylcholine receptorsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2006A. V. Shakirzyanova Abstract Functional interactions between presynaptic adenosine and acetylcholine (ACh) autoreceptors were studied at the frog neuromuscular junction by recording miniature end-plate potentials (MEPPs) during bath or local application of agonists. The frequency of MEPPs was reduced by adenosine acting on presynaptic adenosine A1 receptors (EC50 = 1.1 µm) or by carbachol acting on muscarinic M2 receptors (EC50 = 1.8 µm). However, carbachol did not produce the depressant effect when it was applied after the action of adenosine had reached its maximum. This phenomenon implied that the negative cross-talk (occlusion) had occurred between A1 and M2 receptors. Moreover, the occlusion was receptor-specific as ATP applied in the presence of adenosine continued to depress MEPP frequency. Muscarinic antagonists [atropine or 1-[[2-[(diethylamino)methyl)-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido [2,3-b][1,4]benzodiazepine-6-one) (AFDX-116)] had no effect on the inhibitory action of adenosine and adenosine antagonists [8-(p -sulfophenyl)theophylline (8-SPT) or 1,3-dipropyl-8-cyclopentylxanthine (DPCPX)] had no effect on the action of carbachol. These data suggested that membrane,delimited interactions did not occur between A1 and M2 receptors. Both carbachol and adenosine similarly inhibited quantal release triggered by high potassium, ionomycin or sucrose. These results indicated a convergence of intracellular pathways activated by M2 and A1 receptors to a common presynaptic effector located downstream of Ca2+ influx. We propose that the negative cross-talk between two major autoreceptors could take place during intense synaptic activity and thereby attenuate the presynaptic inhibitory effects of ACh and adenosine. [source] Disparate cholinergic currents in rat principal trigeminal sensory nucleus neurons mediated by M1 and M2 receptors: a possible mechanism for selective gating of afferent sensory neurotransmissionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2006Kristi A. Kohlmeier Abstract Neurons situated in the principal sensory trigeminal nucleus (PSTN) convey orofacial sensory inputs to thalamic relay regions and higher brain centres, and the excitability of these ascending tract cells is modulated across sleep/wakefulness states and during pain conditions. Moreover, acetylcholine release changes profoundly across sleep/wakefulness states and ascending sensory neurotransmission is altered by cholinergic agonists. An intriguing possibility is, therefore, that cholinergic mechanisms mediate such state-dependent modulation of PSTN tract neurons. We tested the hypotheses that cholinergic agonists can modulate PSTN cell excitability and that such effects are mediated by muscarinic receptor subtypes, using patch-clamp methods in rat and mouse. In all examined cells, carbachol elicited an electrophysiological response that was independent of action potential generation as it persisted in the presence of tetrodotoxin. Responses were of three types: depolarization, hyperpolarization or a biphasic response consisting of hyperpolarization followed by depolarization. In voltage-clamp mode, carbachol evoked corresponding inward, outward or biphasic currents. Moreover, immunostaining for the vesicle-associated choline transporter showed cholinergic innervation of the PSTN. Using muscarinic receptor antagonists, we found that carbachol-elicited PSTN neuron hyperpolarization was mediated by M2 receptors and depolarization, in large part, by M1 receptors. These data suggest that acetylcholine acting on M1 and M2 receptors may contribute to selective excitability enhancement or depression in individual, rostrally projecting sensory neurons. Such selective gating effects via cholinergic input may play a functional role in modulation of ascending sensory transmission, including across behavioral states typified by distinct cholinergic tone, e.g. sleep/wakefulness arousal levels or neuropathic pain conditions. [source] Modulation by adenosine of both muscarinic M1 -facilitation and M2 -inhibition of [3H]-acetylcholine release from the rat motor nerve terminalsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2002Laura Oliveira Abstract The crosstalk between adenosine and muscarinic autoreceptors regulating evoked [3H]-acetylcholine ([3H]-ACh) release was investigated on rat phrenic nerve-hemidiaphragm preparations. Motor nerve terminals possess facilitatory M1 and inhibitory M2 autoreceptors that can be activated by McN-A-343 (1,30 µm) and oxotremorine (0.3,100 µm), respectively. The muscarinic receptor antagonist, dicyclomine (3 nm,10 µm), caused a biphasic (inhibitory/facilitatory) effect, indicating that M1 -facilitation prevails during 5 Hz stimulation trains. Concomitant activation of AF,DX 116-sensitive M2 receptors was partially attenuated, as pretreatment with M1 antagonists, muscarinic toxin 7 (MT-7, 0.1 nm) and pirenzepine (1 nm), significantly enhanced inhibition by oxotremorine. Activation of A2A -adenosine receptors with CGS 21680C (2 nm) (i) potentiated oxotremorine inhibition, and (ii) shifted McN-A-343-induced facilitation into a small inhibitory effect. Conversely, the A1 -receptor agonist, R- N6 -phenylisopropyl adenosine (R-PIA, 100 nm), attenuated the inhibitory effect of oxotremorine, without changing facilitation by McN-A-343. Synergism between A2A and M2 receptors is regulated by a reciprocal interaction with facilitatory M1 receptors, which may be prevented by pirenzepine (1 nm). During 50 Hz-bursts, facilitation (M1) of [3H]-ACh release by McN-A-343 disappeared, while the inhibitory (M2) effect of oxotremorine became predominant. This muscarinic shift results from the interplay with A2A receptors, as it was precluded by the selective A2A receptor antagonist, ZM 241385 (10 nm). In conclusion, when the muscarinic M1 positive feedback loop is fully operative, negative regulation of ACh release is mediated by adenosine A1 receptors. During high frequency bursts, tonic activation of A2A receptors promotes M2 autoinhibition by braking the M1 receptor operated counteraction. [source] Receptor architecture of human cingulate cortex: Evaluation of the four-region neurobiological modelHUMAN BRAIN MAPPING, Issue 8 2009Nicola Palomero-Gallagher Abstract The structural and functional organization of the human cingulate cortex is an ongoing focus; however, human imaging studies continue to use the century-old Brodmann concept of a two region cingulate cortex. Recently, a four-region neurobiological model was proposed based on structural, circuitry, and functional imaging observations. It encompasses the anterior cingulate, midcingulate, posterior cingulate, and retrosplenial cortices (ACC, MCC, PCC, and RSC, respectively). For the first time, this study performs multireceptor autoradiography of 15 neurotransmitter receptor ligands and multivariate statistics on human whole brain postmortem samples covering the entire cingulate cortex. We evaluated the validity of Brodmann's duality concept and of the four-region model using a hierarchical clustering analysis of receptor binding according to the degree of similarity of each area's receptor architecture. We could not find support for Brodmann's dual cingulate concept, because the anterior part of his area 24 has significantly higher AMPA, kainate, GABAB, benzodiazepine, and M3 but lower NMDA and GABAA binding site densities than the posterior part. The hierarchical clustering analysis distinguished ACC, MCC, PCC, and RSC as independent regions. The ACC has highest AMPA, kainate, ,2, 5-HT1A, and D1 but lowest GABAA densities. The MCC has lowest AMPA, kainate, ,2, and D1 densities. Area 25 in ACC is similar in receptor-architecture to MCC, particularly the NMDA, GABAA, GABAB, and M2 receptors. The PCC and RSC differ in the higher M1 and ,1 but lower M3 densities of PCC. Thus, multireceptor autoradiography supports the four-region neurobiological model of the cingulate cortex. Hum Brain Mapp, 2009. © 2008 Wiley-Liss, Inc. [source] Medicinal chemistry and therapeutic potential of muscarinic M3 antagonistsMEDICINAL RESEARCH REVIEWS, Issue 6 2009Ilaria Peretto Abstract Muscarinic acetylcholine receptors belong to the G-protein-coupled receptors family. Currently five different receptor subtypes have been identified and cloned. M3 receptor subtypes are coupled to Gq family proteins and increase phosphatidyl inositol hydrolysis and calcium release from internal stores. They are widely distributed both in the central nervous system and in the periphery. At the central level, M3 receptor subtypes are involved in modulation of neurotransmitter release, temperature homeostasis, and food intake, while in the periphery they induce smooth muscle contraction, gland secretion, indirect relaxation of vascular smooth muscle, and miosis. The main therapeutic applications of M3 antagonists include overactive bladder (OAB), chronic obstructive pulmonary disease (COPD), and pain-predominant irritable bowel syndrome (IBS). The introduction of selective M3 antagonists has not improved clinical efficacy compared with the old non-selective antimuscarinics but has reduced the rate of adverse events mediated by the blockade of cardiac M2 receptors (tachycardia) and central M1 receptors (cognitive impairment). Improved tolerability has been obtained also with controlled release or with inhaled formulations. However, there is still a need for safer M3 antagonists for the treatment of COPD and better-tolerated and more effective compounds for the therapy of OAB. New selective muscarinic M3 antagonists currently in early discovery and under development have been designed to address these issues. However, as M3 receptors are widely located in various tissues including salivary glands, gut smooth muscles, iris, and ciliary muscles, further clinical improvements may derive from the discovery and the development of new compounds with tissue rather than muscarinic receptor subtype selectivity. © 2009 Wiley Periodicals, Inc. Med Res Rev, 29, No. 6, 867,902, 2009 [source] Polymethylene tetraamine backbone as template for the development of biologically active polyaminesMEDICINAL RESEARCH REVIEWS, Issue 2 2003Carlo Melchiorre Abstract The concept that polyamines may represent a universal template in the receptor recognition process is embodied in the design of ligands for different biological targets. As a matter of fact, the insertion of different pharmacophores onto the polymethylene tetraamine backbone can tune both affinity and selectivity for any given receptor. The application of this approach provided a prospect of modifying benextramine (1) structure to achieve specific recognition of muscarinic receptors that led to the discovery of methoctramine (2), which is widely used as a pharmacological tool for muscarinic receptor characterization. In turn, appropriate structural modifications performed on the structure of methoctramine led to the discovery of new polyamines endowed with high affinity and selectivity for (a) muscarinic receptor subtypes, (b) Gi proteins, and (c) muscle-type nicotinic receptors. Thus, polyamines tripitramine (9) and spirotramine (33), among others, were designed, which were shown to be highly selective for muscarinic M2 and M1 receptors, respectively. Several polyamines have been discovered, which inhibit noncompetitively a closed state of the nicotinic receptor. These ligands, such as 66, resulted in important tools for elucidating the mode and site of interaction of polyamines with the ion channel. It was discovered that reducing the flexibility of the diaminohexane spacer of methoctramine led to polyamines, such as 70, which are endowed with a biological profile significantly different from that of the prototype. Most likely, tetraamine (70) is a potent activator of Gi proteins. Finally, the universal template approach formed the basis for modifying benextramine (1) structure to the design of ligands, which display affinity for acetylcholinesterase and muscarinic M2 receptors. Thus, these polyamines, such as caproctamine (78), could have potential in the investigation of Alzheimer disease. © 2002 Wiley Periodicals, Inc. Med Res Rev, 23, No. 2, 200,233, 2003 [source] Detection of muscarinic receptor subtypes in human urinary bladder mucosa: Age and gender-dependent modifications,,§NEUROUROLOGY AND URODYNAMICS, Issue 5 2008Nicola Arrighi Abstract Aims Muscarinic receptor subtypes expressed in the human urinary bladder mucosa were characterized, investigating whether there were gender-dependent differences and if aging could induce changes in their expression. Methods The study was carried out on 34 subjects, 22 men and 12 women, divided in four groups, based on gender and age. Gene expression was evaluated by quantitative RT-PCR. The Western blot was performed using the 4,12% NuPAGE Bis,Tris Gel System. Results The molecular expression of each subtype of the M1 receptor family was observed and it was not influenced either by gender or age. M2 receptor family transcripts revealed that both M2 and M4 were detected and that the M2 transcripts were modified by both gender and age. Indeed, M2 mRNA was lower in old rather than adult men (P,<,0.05), but higher in rather old than adult women (P,<,0.05). Further, adult men expressed more M2 mRNA than adult women (P,<,0.05), while the opposite was detected in old age (P,<,0.05). The Western blot followed by quantification confirmed that the mRNAs were translated into proteins, and that the M2 subtype showed similar modifications found at molecular level. Discussion The selective modification of M2 receptors observed at the urinary bladder mucosa levels indicates that this anatomical structure could play an active role in the pathophysiology of micturition and supports evidence suggesting an effect of antimuscarinic drugs at this level. Whether these results may influence the age-dependent development of micturition disorders remains to be determined. Neurourol. Urodynam. 27:421,428, 2008. © 2007 Wiley-Liss, Inc. [source] M2 mediated contractions of human bladder from organ donors is associated with an increase in urothelial muscarinic receptors,NEUROUROLOGY AND URODYNAMICS, Issue 1 2007Alan S. Braverman Abstract Aims Previous studies have shown increased density of M2 receptors in hypertrophied rat bladders that possess an M2 contractile phenotype. The aim of the current study is to determine whether human bladders with an M2 contractile phenotype also have a greater density of bladder M2 receptors. Materials and Methods Human bladders were obtained from 24 different organ transplant donors. Darifenacin and methoctramine affinity was determined by the rightward shift of cumulative carbachol concentration contractile response curves for each bladder. Radioligand binding and immunoprecipitation was used to quantify M2 and M3 subtypes in isolated detrusor muscle and urothelium. In addition, pig bladder muscle and urothelial receptors were quantified for comparison. Results In the human urothelium total, M2 and M3 muscarinic receptor density is significantly negatively correlated with the affinity of darifenacin for inhibition of contraction of the detrusor muscle. In the detrusor muscle there is no correlation between receptor density and darifenacin affinity for inhibition of contraction. Muscarinic receptor density is greater in the muscle than in the urothelium in human bladders whereas in the pig bladder the density is greater in the urothelium than in the muscle. Conclusions The greater density of urothelial muscarinic receptors in human bladders with lower darifenacin affinity, indicative of a greater contribution of M2 receptors to the contractile response, points towards a possible role of the urothelium in controlling M2 mediated contractile phenotype. In comparison between human and pig bladders, the distribution of muscarinic receptor subtypes in the muscle and urothelium are quite different. Neurourol. Urodynam. © 2006 Wiley-Liss, Inc. [source] Muscarinic receptor subtypes in neuronal and non-neuronal cholinergic functionAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 3 2006R. M. Eglen Summary 1 Muscarinic M1,M5 receptors mediate the metabotropic actions of acetylcholine in the nervous system. A growing body of data indicate they also mediate autocrine functions of the molecule. The availability of novel and selective muscarinic agonists and antagonists, as well as in vivo gene disruption techniques, has clarified the roles of muscarinic receptors in mediating both functions of acetylcholine. 2 Selective M1 agonists or mixed M1 agonists/M2 antagonists may provide an approach to the treatment of cognitive disorders, while M3 antagonism, or mixed M2/M3 antagonists, are approved for the treatment of contractility disorders including overactive bladder and chronic obstructive pulmonary disease. Preclinical data suggest that selective agonism of the M4 receptor will provide novel anti-nociceptive agents, while therapeutics-based upon agonism or antagonism of the muscarinic M5 receptor have yet to be reported. 3 The autocrine functions of muscarinic receptors broadly fall into two areas , control of cell growth or proliferation and mediation of the release of chemical mediators from epithelial cells, ultimately causing muscle relaxation. The former particularly are involved in embryological development, oncogenesis, keratinocyte function and immune responsiveness. The latter regulate contractility of smooth muscle in the vasculature, airways and urinary bladder. 4 Most attention has focused on muscarinic M1 or M3 receptors which mediate lymphocyte immunoresponsiveness, cell migration and release of smooth muscle relaxant factors. Muscarinic M4 receptors are implicated in the regulation of keratinocyte adhesion and M2 receptors in stem cell proliferation and development. Little data are available concerning the M5 receptor, partly due to the difficulties in defining the subtype pharmacologically. 5 The autocrine functions of acetylcholine, like those in the nervous system, involve activation of several muscarinic receptor subtypes. Consequently, the role of these subtypes in autocrine, as well neuronal cholinergic systems, significantly expands their importance in physiology and pathophysiology. [source] Regulation of bladder muscarinic receptor subtypes by experimental pathologiesAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 3 2006M. R. Ruggieri Sr Summary 1 The M3 muscarinic receptor subtype is widely accepted as the receptor on smooth muscle cells that mediates cholinergic contraction of the normal urinary bladder and other smooth muscle tissues, however, we have found that the M2 receptor participates in contraction under certain abnormal conditions. The aim of this study was to determine the effects of various experimental pathologies on the muscarinic receptor subtype mediating urinary bladder contraction. 2 Experimental pathologies resulting in bladder hypertrophy (denervation and outlet obstruction) result in an up-regulation of bladder M2 receptors and a change in the receptor subtype mediating contraction from M3 towards M2. Preventing the denervation-induced bladder hypertrophy by urinary diversion prevents this shift in contractile phenotype indicating that hypertrophy is responsible as opposed to denervation per se. 3 The hypertrophy-induced increase in M2 receptor density and contractile response is accompanied by an increase in the tissue concentrations of mRNA coding for the M2 receptor subtype, however, M3 receptor protein density does not correlate with changes in M3 receptor tissue mRNA concentrations across different experimental pathologies. 4 This shift in contractile phenotype from M3 towards M2 subtype is also observed in aged male Sprague,Dawley rats but not females or either sex of the Fisher344 strain of rats. 5 Four repeated, sequential agonist concentration response curves also cause this shift in contractile phenotype in normal rat bladder strips in vitro, as evidenced by a decrease in the affinity of the M3 selective antagonist p -fluoro-hexahydro-sila-diphenidol (p -F-HHSiD). 6 A similar decrease in the contractile affinity of M3 selective antagonists (darifenacin and p -F-HHSiD) is also observed in bladder specimens from patients with neurogenic bladder as well as certain organ transplant donors. 7 It is concluded that although the M3 receptor subtype predominately mediates contraction under normal circumstances, the M2 receptor subtype can take over a contractile role when the M3 subtype becomes inactivated by, for example, repeated agonist exposures or bladder hypertrophy. This finding has substantial implications for the clinical treatment of abnormal bladder contractions. [source] Gq/11 and Gi/o activation profiles in CHO cells expressing human muscarinic acetylcholine receptors: dependence on agonist as well as receptor-subtypeBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2001Elizabeth C Akam Profiles of G protein activation have been assessed using a [35S]-GTP,S binding/immunoprecipitation strategy in Chinese hamster ovary cells expressing either M1, M2, M3 or M4 muscarinic acetylcholine (mACh) receptor subtypes, where expression levels of M1 and M3, or M2 and M4 receptors were approximately equal. Maximal [35S]-GTP,S binding to Gq/11, stimulated by M1/M3 receptors, or Gi1 , 3, stimulated by M2/M4 receptors occurred within approximately 2 min of agonist addition. The increases in Gq/11,-[35S]-GTP,S binding after M1 and M3 receptor stimulation differed substantially, with M1 receptors causing a 2 , 3 fold greater increase in [35S]-GTP,S binding and requiring 5 fold lower concentrations of methacholine to stimulate a half-maximal response. Comparison of M2 and M4 receptor-mediated Gi1 , 3,-[35S]-GTP,S binding also revealed differences, with M2 receptors causing a greater increase in Gi1 , 3, activation and requiring 10 fold lower concentrations of methacholine to stimulate a half-maximal response. Comparison of methacholine- and pilocarpine-mediated effects revealed that the latter partial agonist is more effective in activating Gi3, compared to Gi1/2, for both M2 and M4 receptors. More marked agonist/partial agonist differences were observed with respect to M1/M3 -mediated stimulations of Gq/11,- and Gi1 , 3,-[35S]-GTP,S binding. Whereas coupling to these G, subclasses decreased proportionately for M1 receptor stimulation by these agonists, pilocarpine possesses a greater intrinsic activity at M3 receptors for Gi, versus Gq/11, activation. These data demonstrate that mACh receptor subtype and the nature of the agonist used govern the repertoire of G proteins activated. They also provide insights into how the diversity of coupling can be pharmacologically exploited, and provide a basis for a better understanding of how multiple receptor subtypes can be differentially regulated. British Journal of Pharmacology (2001) 132, 950,958; doi:10.1038/sj.bjp.0703892 [source] | |||||||||||||