Abstract
The muscarinic receptor subtype-activated signal transduction mechanisms mediating rat urinary bladder contraction are incompletely understood. M3 mediates normal rat bladder contractions; however, the M2 receptor subtype has a more dominant role in contractions of the hypertrophied bladder. Normal bladder muscle strips were exposed to inhibitors of enzymes thought to be involved in signal transduction in vitro followed by a single cumulative concentration-response curve to the muscarinic receptor agonist carbachol. The outcome measures were the maximal contraction, the potency of carbachol, and the affinity of the M3 -selective antimuscarinic agent darifenacin for inhibition of contraction. Inhibition of phosphoinositide-specific phospholipase C (PI-PLC) with 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphorylcholine (ET-18-OCH3) reduces carbachol potency and reduces darifenacin affinity, whereas inhibition of phosphatidyl choline-specific phospholipase C (PC-PLC) with O-tricyclo[5.2.1.02,6]dec-9-yl dithiocarbonate potassium salt (D609) attenuates the carbachol maximal contraction. Inhibition of rho kinase with (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride (Y-27632) reduces carbachol potency and increases darifenacin affinity. Inhibition of rho kinase, protein kinase A (PKA), and protein kinase G (PKG) with 1-(5-isoquinolinesulfonyl)-homopiperazine·HCl (HA-1077) reduces the carbachol maximal contraction, carbachol potency, and darifenacin affinity. Inhibition of protein kinase C (PKC) with chelerythrine increases darifenacin affinity, whereas inhibition of rho kinase, PKA, PKG, and PKC with 1-(5-isoquinolinesulfonyl)-2-methylpiperazine·2HCl (H7) reduces the carbachol maximum and carbachol potency while increasing darifenacin affinity. Inhibition of rho kinase, PKA, and PKG with N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide·2HCl (H89) reduces carbachol maximum and carbachol potency. Both the M2 and the M3 receptor subtype are involved in normal rat bladder contractions. The M3subtype seems to mediate contraction by activation of PI-PLC, PC-PLC, and PKA, whereas the M2 signal transduction cascade may include activation of rho kinase, PKC, and an additional contractile signal transduction mechanism independent of rho kinase or PKC.
Footnotes
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This study was supported by Public Health Service Grant R01 DK43333 (to M.R.R.).
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doi:10.1124/jpet.105.097303.
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ABBREVIATIONS: IP3, inositol 1,4,5-trisphosphate; PI-PLC, phosphoinositide specific phospholipase C; U73122, 1-[6-[[17β-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione; ET-18-OCH3, 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphorylcholine; D609, O-tricyclo[5.2.1.02,6]dec-9-yl dithiocarbonate potassium salt; Y-27632, (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride; HA-1077, 1-(5-isoquinolinesulfonyl)-homopiperazine·HCl; H7, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine·2HCl; H89, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide·2HCl; ROCK, rho kinase; PKG, protein kinase G; PKA, protein kinase A; PKC, protein kinase C; PC-PLC, phosphatidyl choline specific phospholipase C; CRC, concentration-response curve; CPI-17, protein kinase C-potentiated phosphatase inhibitor of 17 kDa; MLC, myosin light chain.
- Received October 17, 2005.
- Accepted October 20, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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