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 M 1 -selective pirenzepine, the M 2 -selective methoctramine and the M 3 -selective darifenacin. All antagonists yielded Schild-plots with a slope close to unity. The order of potency (atropine5darifenacin4pirenzepine4methoctramine) as well as the estimated antagonist a nities suggested that contraction of the human bladder occurs predominantly if not exclusively via the M 3 receptor.

We have investigated the role of several protein kinases in carbachol-stimulated, M 3 muscarinic receptor-mediated contraction of rat urinary bladder. Concentration-response curves for the muscarinic receptor agonist carbachol were generated in the presence of multiple concentrations of inhibitors of various protein kinases, their inactive controls, or their vehicles. Bladder contraction was not significantly inhibited by three protein kinase C inhibitors (chelerythrine, 1-10 M; calphostin C, 0.1-1 M; and 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide (Gö 6850), 1-10 M), by the tyrosine kinase inhibitor genistein or its inactive control daidzein (3-30 M each), or by two inhibitors of activation of mitogenactivated protein kinase [10 -100 M 2Ј-amino-3Ј-methoxyflavone (PD 98,059) and 3-30 M 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U 124)] or their negative control 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U 126) (3-30 M). Although high concentrations of wortmannin (3-30 M) inhibited bladder contraction, this was not mimicked by another inhibitor of phosphatidylinositol-3-kinase, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY 294,002) (3-30 M) and, hence, was more likely due to direct inhibition of myosin light chain kinase by wortmannin than to an involvement of phosphatidylinositol-3-kinase. In contrast, trans-4-[(1R)-1-aminoethyl]-N-4-pyridinylcyclohexanecarboxamide (Y 27,632) (1-10 M), an inhibitor of rho-associated kinases, concentration-dependently and effectively attenuated the carbachol responses. We conclude that carbachol-induced contraction of rat urinary bladder does not involve protein kinase C, phosphatidylinositol-3-kinase, tyrosine kinases, or extracellular signal-regulated kinases; in contrast, rhoassociated kinases appear to play an important role in the regulation of bladder contraction.Muscarinic acetylcholine receptors are the physiologically most important mechanism to mediate contraction of the urinary bladder (Andersson, 1993). Although rat bladder expresses more M 2 than M 3 receptors, contractile responses to the exogenous muscarinic agonist carbachol and to endogenous agonists released by field stimulation occur predominantly, if not exclusively, via M 3 receptors in rats (Longhurst et al