Signal Transduction Underlying Carbachol-Induced Contraction of Human Urinary Bladder

The present study was designed to reexamine the muscarinic acetylcholine receptor subtype mediating carbachol-induced contraction of human urinary bladder and to investigate the underlying signal transduction. Based upon the nonselective tolterodine, the highly M2-selective ( R )-4-{2-[3-(4-methoxy-benzoylamino)-benzyl]-piperidin-1-ylmethyl}piperidine-1-carboxylic acid amide (Ro-320-6206), and the highly M3-selective darifenacin and 3-(1-carbamoyl-1,1-diphenylmethyl)-1-(4-methoxyphenylethyl)pyrrolidine (APP), contraction occurs via M3 receptors. The phospholipase C inhibitor 1-(6-[([17β]-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl)-1H-pyrrole-2,5-dione (U 73,122) (1-10 μM) did not significantly affect carbachol-stimulated bladder contraction. The phospholipase D inhibitor butan-1-ol relative to its negative control butan-2-ol (0.3% each) caused small but detectable inhibition of carbachol-induced bladder contraction. The Ca2+ entry blocker nifedipine (10-100 nM) strongly inhibited carbachol-induced bladder contraction. In contrast, 1-[β-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1 H -imidazole HCl (SK&F 96,365) (1-10 μM), an inhibitor of store-operated Ca2+ channels, caused little inhibition. The protein kinase C inhibitor bisindolylmaleimide I (1-10 μM) did not significantly affected carbachol-induced bladder contraction. In contrast, trans -4-[(1 R )-1-aminoethyl]- N -4-pyridinylcyclohexanecarboxamide (Y 27,632) (1-10 μM), an inhibitor of rho-associated kinases, concentration dependently and effectively attenuated the carbachol responses. We conclude that carbachol-induced contraction of human urinary bladder via M3 receptors largely depends on Ca2+ entry through nifedipine-sensitive channels and activation of a rho kinase, whereas phospholipase D and store-operated Ca2+ channels contribute only in a minor way. Surprisingly, phospholipase C or protein kinase C do not seem to be involved to a relevant extent.