Muscarinic Receptors Distributed in the Lower Urinary Tract

ABSTRACT

Acetylcholine (Ach) acting on the muscarinic receptors is the major stimulus for the detrusor inducing contraction if the bladder is distended and the bladder volume is at the threshold. There are 5 types muscarinic receptor subtypes cloned (M1-M5). Among them, the M2 subtype distributed dominantly in amount in the detrusor and its role seems to be primarily by blocking stimuli from cAMP-coupled receptors that induce relaxation. In contrast, through M3 receptors on the detrusor the strong contractile stimulus evoked even if its distribution in secondarily common. The excitatory M1 and inhibitory M2 and M4 subtypes are also expresswed prejunctionally. Like detrusor, urothelium also expressed all subtypes of muscarinic receptors, and on stimulation it releases factors affecting bladder afferents and smooth muscle. During inflammation, the expression of muscarinic M5 receptors is increased, particularly in the urothelium, together with a cholinergic-induced production of nitric oxide in the mucosa. This review will be discussed expression and functional effects of muscarinic receptors in the lower urinary tract. Clinical aspects of the different muscarinic receptors and roles in the pathologic conditions included in this discussions.