Muscarinic receptor subtypes modulating smooth muscle contractility in the urinary bladder

Drug therapy for urinary incontinence

Drugs used for treatment of urinary incontinence may act on the central nervous system (CNS) or peripherally. Few drugs with a defined CNS site of action are available for treatment of urine storage disorders; most of those currently used have a peripheral site of action. To treat bladder overactivity associated with urgency and urge incontinence, antimuscarinic drugs, alpha-adrenoceptor antagonists, beta-adrenoceptor agonists, prostaglandin synthesis inhibitors, and several other agents most often developed for non-urological indications, are employed. Current treatment is based on the use of antimuscarinic drugs, and oxybutynin is, despite a high incidence of side-effects, the gold standard. Pharmacological treatment of stress incontinence has had limited success, and only alpha-adrenoceptor agonists, with and without combination with oestrogens have had a documented effect. New drugs, specifically directed at treatment of urine storage disorders, are desirable.

Nicotinic acetylcholine receptors in the autonomic control of bladder function

Micturition is achieved through complex neurological mechanisms involving somatic, autonomic and central components. This article briefly reviews recent findings on the autonomic control of urinary bladder function. Neuronal nicotinic acetylcholine receptors mediate fast synaptic transmission in autonomic ganglia, and activation of nicotinic receptors in parasympathetic bladder neurons produces contraction of the detrusor muscle. Autonomic ganglia contain transcripts for the alpha(3), alpha(4), alpha(5), alpha(7), beta(2) and beta(4) nicotinic subunits, which can assemble to form multiple nicotinic receptor subtypes, but the exact nicotinic receptor subunit composition in bladder ganglia is unknown. Mutant mice lacking the alpha(3) or the beta(2) and the beta(4) nicotinic subunits have enlarged bladders with dribbling urination and develop urinary infection and bladder stones. Bladder strips from alpha(3) null mice do not respond to nicotine but contract when stimulated with a muscarinic agonist or electric field stimulation. Mice lacking the beta(2) subunit have no overt bladder phenotype, and their bladders contract in response to nicotine. Surprisingly, bladder strips from beta(4) mutant mice do not respond to nicotine despite the absence of major bladder dysfunction in vivo. These findings suggest that nicotinic receptors containing the alpha(3) and the beta(4) subunits are necessary for normal bladder function.