Since muscarinic receptors appear to be the physiologically most important control system for urinary bladder contraction, we have characterized the receptor subtype mediating contraction in response to the muscarinic agonist carbachol in the human bladder. Experiments were based on four antagonists, the non-selective atropine, the M1-selective pirenzepine, the M2-selective methoctramine and the M3-selective darifenacin. All antagonists yielded Schild-plots with a slope close to unity. The order of potency (atropinedarifenacin>pirenzepine>methoctramine) as well as the estimated antagonist affinities suggested that contraction of the human bladder occurs predominantly if not exclusively via the M3 receptor.
British Journal of Pharmacology (2002) 136, 641–644; doi:10.1038/sj.bjp.0704781