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|Title:||An investigation of tissue-specific pharmacologies and inverse agonism at muscarinic acetylcholine receptors.|
|Authors:||Nelson, Carl Philip.|
|Presented at:||University of Leicester|
|Abstract:||Evidence presented in this thesis supports the notion that certain muscarinic antagonists exhibit a greater functional affinity for the inhibition of M3 muscarinic acetylcholine (mACh) receptor-mediated phosphoinositide turnover in guinea-pig urinary bladder than for M3 receptor-mediated responses in the submandibular salivary gland of the same species. The present study suggests that the observed tissue-dependent pharmacologies cannot be explained in terms of multiple receptor subtypes. The muscarinic antagonists found to display such 'functional selectivity' in this investigation are used in the pharmacological management of overactive bladder, so it is possible that these properties contribute to the favourable side-effect profiles of some of these drags. The potential molecular mechanisms underlying these observations are discussed. To investigate the inverse agonist properties of these, and other, mACh receptor antagonists, a constitutively-active, mutant (CAM) M2 mACh receptor was generated by a single amino acid change (N410Y) at the junction between the sixth transmembrane domain and the third extracellular loop of the M2 receptor. The present study provides the first detailed characterisation of a CAM M2 mACh receptor, demonstrating many of the hallmark features of a CAM receptor, including enhanced agonist-independent signalling, increased agonist binding affinity and functional potency and an increased partial agonist efficacy. All of the ligands assayed (previously classified as 'antagonists' at the M2 receptor), similarly reduced the constitutive activity of the mutant receptor, indicating that they should be re-classified as inverse agonists at the M2 mACh receptor. The CAM M2 mACh receptor was also expressed at substantially lower levels than the wild-type receptor, but overnight incubation with atropine caused a significant up-regulation of cell surface receptor expression. However, not all inverse agonists were capable of up-regulating the CAM M2 receptor. The implications of these findings for the clinical use of muscarinic antagonists and for mACh receptor signalling in general are discussed.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Cell Physiology and Pharmacology|
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