title: Muscarinic receptor subtypes in airways.
abstract: Muscarinic receptor subtypes in the airways appear to subserve different physiological functions. M1-receptors facilitate neurotransmission through parasympathetic ganglia and enhance cholinergic reflexes, but are also localized to alveolar walls. M2-receptors act as autoreceptors on post-ganglionic cholinergic nerves and inhibit acetylcholine release. There is some evidence that they may be defective in asthma (as a consequence of airway inflammation?) and this may enhance cholinergic reflexes and account for beta-blocker-induced asthma. M2-receptors in airway smooth muscle may also counteract the bronchodilator action of beta-agonists. M3-receptors mediate contractile responses in airway smooth muscle via phosphoinositide hydrolysis, and are the predominant receptors on submucosal glands and airway vascular endothelium. M4- and M5-receptors have not been identified in human airways, but in rabbit lung M4-receptors are expressed on alveolar walls and smooth muscle. Anticholinergic drugs which selectively block M3 and M1-receptors may have an advantage over currently used non-selective antagonists in the treatment of airway obstruction.
authors.affiliation: National Heart & Lung Institute, London, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Barnes
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D016084:Bronchoconstriction / Q000187:drug effects; D005728:Ganglia, Sympathetic / Q000502:physiology; D006801:Humans; D008168:Lung / Q000294:innervation / Q000378:metabolism*; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology; D011976:Receptors, Muscarinic / Q000145:classification / Q000378:metabolism*
chemical_list: D011976:Receptors, Muscarinic; D000109:Acetylcholine