scholarly journals Muscarinic agonist, (±)-quinuclidin-3-yl-(4-fluorophenethyl)(phenyl)carbamate: High affinity, but low subtype selectivity for human M1 – M5 muscarinic acetylcholine receptors

2019 ◽  
Vol 29 (3) ◽  
pp. 471-476
Author(s):  
Na-Ra Lee ◽  
Satheesh Gujarathi ◽  
Shobanbabu Bommagani ◽  
Kiranbabu Siripurapu ◽  
Guangrong Zheng ◽  
...  
Keyword(s):  
Acetylcholine Receptors ◽  
Muscarinic Acetylcholine Receptors ◽  
Muscarinic Agonist ◽  
Muscarinic Acetylcholine ◽  
High Affinity ◽  
Subtype Selectivity

scholarly journals Pharmaceutical Assessment Suggests Locomotion Hyperactivity in Zebrafish Triggered by Arecoline Might Be Associated with Multiple Muscarinic Acetylcholine Receptors Activation

Toxins ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 259
Author(s):  
Petrus Siregar ◽  
Gilbert Audira ◽  
Ling-Yi Feng ◽  
Jia-Hau Lee ◽  
Fiorency Santoso ◽  
...  
Keyword(s):  
Molecular Docking ◽  
Adverse Effects ◽  
Acetylcholine Receptors ◽  
Docking Simulation ◽  
Muscarinic Acetylcholine Receptors ◽  
Mechanistic Study ◽  
Muscarinic Agonist ◽  
Muscarinic Acetylcholine ◽  
Zebrafish Larvae ◽  
Exposure Experiment

Arecoline is one of the nicotinic acid-based alkaloids, which is found in the betel nut. In addition to its function as a muscarinic agonist, arecoline exhibits several adverse effects, such as inducing growth retardation and causing developmental defects in animal embryos, including zebrafish, chicken, and mice. In this study, we aimed to study the potential adverse effects of waterborne arecoline exposure on zebrafish larvae locomotor activity and investigate the possible mechanism of the arecoline effects in zebrafish behavior. The zebrafish behavior analysis, together with molecular docking and the antagonist co-exposure experiment using muscarinic acetylcholine receptor antagonists were conducted. Zebrafish larvae aged 96 h post-fertilization (hpf) were exposed to different concentrations (0.001, 0.01, 0.1, and 1 ppm) of arecoline for 30 min and 24 h, respectively, to find out the effect of arecoline in different time exposures. Locomotor activities were measured and quantified at 120 hpf. The results showed that arecoline caused zebrafish larvae locomotor hyperactivities, even at a very low concentration. For the mechanistic study, we conducted a structure-based molecular docking simulation and antagonist co-exposure experiment to explore the potential interactions between arecoline and eight subtypes, namely, M1a, M2a, M2b, M3a, M3b, M4a, M5a, and M5b, of zebrafish endogenous muscarinic acetylcholine receptors (mAChRs). Arecoline was predicted to show a strong binding affinity to most of the subtypes. We also discovered that the locomotion hyperactivity phenotypes triggered by arecoline could be rescued by co-incubating it with M1 to M4 mAChR antagonists. Taken together, by a pharmacological approach, we demonstrated that arecoline functions as a highly potent hyperactivity-stimulating compound in zebrafish that is mediated by multiple muscarinic acetylcholine receptors.

scholarly journals Characterization of muscarinic acetylcholine receptors in the avian salt gland.

1981 ◽  
Vol 91 (3) ◽  
pp. 781-789 ◽  
Author(s):  
S R Hootman ◽  
S A Ernst
Keyword(s):  
Salt Stress ◽  
Acetylcholine Receptors ◽  
Specific Binding ◽  
Salt Gland ◽  
Fluid Secretion ◽  
Transport Processes ◽  
Muscarinic Acetylcholine Receptors ◽  
Cholinergic Antagonists ◽  
Muscarinic Acetylcholine ◽  
High Affinity

Electrolyte and fluid secretion by the avian salt gland is regulated by activation of muscarinic acetylcholine receptors (R). In this study, these receptors were characterized and quantitated in homogenates of salt gland from domestic ducks adapted to conditions of low (freshwater, FW) and high (saltwater, SW) salt stress using the cholinergic antagonist [3H]-quinuclidinyl benzilate (QNB). Specific binding of the antagonist to receptors in both FW- and SW-adapted glands reveals a single population of high affinity binding sites (KdFW = 40.1 +/- 3.0 pM; KdSW = 35.1 +/- 2.1 pM). Binding is saturable; RLmaxFW = 1.73 +/- 0.10 fmol/micrograms DNA; RLmaxSW = 4.16 +/- 0.31 fmol/micrograms DNA (where L is [3H]QNB and RL the high affinity complex). Calculated average cellular receptor populations of 5,800 sites/cell in FW-adapted glands and 14,100 sites/cell in SW-adapted glands demonstrate that upward regulation of acetylcholine receptors in the secretory epithelium follows chronic salt stress. The receptor exhibits typical pharmacological specificities for muscarinic cholinergic antagonists (QNB, atropine, scopolamine) and agonists (oxotremorine, methacholine, carbachol). In addition, the loop diuretic furosemide, which interferes with ion transport processes in the salt gland, competitively inhibits [3H]QNB binding. Preliminary studies of furosemide effects on [3H]QNB binding to rat exorbital lacrimal gland membranes showed a similar inhibition, although the diuretic had no effect on antagonist binding to rat brain or atrial receptors.

scholarly journals Structure-based discovery of selective positive allosteric modulators of antagonists for the M2 muscarinic acetylcholine receptor

2018 ◽  
Vol 115 (10) ◽  
pp. E2419-E2428 ◽  
Author(s):  
Magdalena Korczynska ◽  
Mary J. Clark ◽  
Celine Valant ◽  
Jun Xu ◽  
Ee Von Moo ◽  
...  
Keyword(s):  
Acetylcholine Receptors ◽  
Muscarinic Acetylcholine Receptor ◽  
Dissociation Rate ◽  
Muscarinic Acetylcholine Receptors ◽  
Neonatal Rat ◽  
Rat Cardiomyocytes ◽  
Muscarinic Acetylcholine ◽  
Adult Rat ◽  
Subtype Selectivity ◽  
Subtype Selective

Subtype-selective antagonists for muscarinic acetylcholine receptors (mAChRs) have long been elusive, owing to the highly conserved orthosteric binding site. However, allosteric sites of these receptors are less conserved, motivating the search for allosteric ligands that modulate agonists or antagonists to confer subtype selectivity. Accordingly, a 4.6 million-molecule library was docked against the structure of the prototypical M2 mAChR, seeking molecules that specifically stabilized antagonist binding. This led us to identify a positive allosteric modulator (PAM) that potentiated the antagonist N-methyl scopolamine (NMS). Structure-based optimization led to compound ’628, which enhanced binding of NMS, and the drug scopolamine itself, with a cooperativity factor (α) of 5.5 and a KB of 1.1 μM, while sparing the endogenous agonist acetylcholine. NMR spectral changes determined for methionine residues reflected changes in the allosteric network. Moreover, ’628 slowed the dissociation rate of NMS from the M2 mAChR by 50-fold, an effect not observed at the other four mAChR subtypes. The specific PAM effect of ’628 on NMS antagonism was conserved in functional assays, including agonist stimulation of [35S]GTPγS binding and ERK 1/2 phosphorylation. Importantly, the selective allostery between ’628 and NMS was retained in membranes from adult rat hypothalamus and in neonatal rat cardiomyocytes, supporting the physiological relevance of this PAM/antagonist approach. This study supports the feasibility of discovering PAMs that confer subtype selectivity to antagonists; molecules like ’628 can convert an armamentarium of potent but nonselective GPCR antagonist drugs into subtype-selective reagents, thus reducing their off-target effects.

scholarly journals Toward an understanding of the structural basis of allostery in muscarinic acetylcholine receptors

2018 ◽  
Vol 150 (10) ◽  
pp. 1360-1372 ◽  
Author(s):  
Wessel A.C. Burger ◽  
Patrick M. Sexton ◽  
Arthur Christopoulos ◽  
David M. Thal
Keyword(s):  
Crystal Structures ◽  
Acetylcholine Receptors ◽  
Allosteric Modulation ◽  
Muscarinic Acetylcholine Receptors ◽  
Therapeutic Interventions ◽  
Structural Basis ◽  
Muscarinic Acetylcholine ◽  
Subtype Selectivity ◽  
Gpcr Activation ◽  
Allosteric Mechanisms

Recent breakthroughs and developments in structural biology have led to a spate of crystal structures for G protein–coupled receptors (GPCRs). This is the case for the muscarinic acetylcholine receptors (mAChRs) where inactive-state structures for four of the five subtypes and two active-state structures for one subtype are available. These mAChR crystal structures have provided new insights into receptor mechanisms, dynamics, and allosteric modulation. This is highly relevant to the mAChRs given that these receptors are an exemplar model system for the study of GPCR allostery. Allosteric mechanisms of the mAChRs are predominantly consistent with a two-state model, albeit with some notable recent exceptions. Herein, we discuss the mechanisms for positive and negative allosteric modulation at the mAChRs and compare and contrast these to evidence offered by pharmacological, biochemical, and computational approaches. This analysis provides insight into the fundamental pharmacological properties exhibited by GPCR allosteric modulators, such as enhanced subtype selectivity, probe dependence, and biased modulation while highlighting the current challenges that remain. Though complex, enhanced molecular understanding of allosteric mechanisms will have considerable influence on our understanding of GPCR activation and signaling and development of therapeutic interventions.

Effect on muscarinic acetylcholine receptors after experimental neuronal ablation in rat colon

1995 ◽  
Vol 269 (6) ◽  
pp. G940-G944
Author(s):  
T. Inoue ◽  
T. Okasora ◽  
E. Okamoto
Keyword(s):  
Myenteric Plexus ◽  
Acetylcholine Receptors ◽  
Treated Group ◽  
Muscarinic Acetylcholine Receptors ◽  
Intraluminal Pressure ◽  
Rat Colon ◽  
Muscarinic Agonist ◽  
Binding Studies ◽  
Muscarinic Acetylcholine ◽  
Denervation Hypersensitivity

The etiology of denervation hypersensitivity was studied using a rat model. Degeneration of the myenteric plexus was produced by direct application of 0.1% benzalkonium chloride to the serosal surface of the distal colon. Thirty days later, the treated group was compared with a control group undergoing a sham operation. The treated group showed that the decreased number of ganglion cells of the myenteric plexus on routine stain and acetylcholinesterase staining demonstrated the myenteric plexus in the treated group diminished acetylcholinesterase activity. Methacholine (1%), a muscarinic agonist, increased intraluminal pressure in treated but not control rats. The dose-response curve of colonic muscle strips to oxotremorine showed a shift to the left, indicating greater sensitivity, in the treated bowel, with a 50% effective dose (ED50) of 2.5 x 10(-8) in treated muscle and 2.2 x 10(-7) in controls. Binding studies using [3H]quinuclidinyl benzilate ([3H]QNB) showed that the specific maximal binding (Bmax) for [3H]QNB was greater in treated than in untreated animals (228 +/- 26.1 and 135 +/- 42.9 fmol/mg protein, respectively; P < 0.01), even though the dissociation constants (Kd) were the same (0.398 +/- 0.083 and 0.406 +/- 0.065). These findings show that acquired denervation hypersensitivity in this model is due to an increase in the number of muscarinic acetylcholine receptors.

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