Abstract
Cyclic AMP is the prototypical second messenger of β-adrenergic receptors, but recent findings have questioned its role in mediating smooth muscle relaxation upon β-adrenergic receptor stimulation. We have investigated the signaling mechanisms underlying β-adrenergic receptor-mediated relaxation of rat urinary bladder. Concentration-response curves for isoproterenol-induced bladder relaxation were generated in the presence or absence of inhibitors, with concomitant experiments using passive tension and KCl-induced precontraction. The adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536; 1 μM), the protein kinase A inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7; 10 μM), N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89; 1 μM), and Rp-adenosine 3′,5′-cyclic monophosphorothioate (Rp-cAMPS; 30 μM), and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ; 3 μM) produced only minor if any inhibition of relaxation against passive tension or KCl-induced precontraction. Among various potassium channel inhibitors, BaCl2 (10 μM), tetraethylammonium (3 μM), apamin (300 nM), and glibenclamide (10 μM) did not inhibit isoproterenol-induced relaxation. Some inhibition of the isoproterenol effects against KCl-induced tone but not against passive tension was seen with inhibitors of calcium-dependent potassium channels such as charybdotoxin and iberiotoxin (30 nM each). A combination of SQ 22,536 and ODQ significantly inhibited relaxation against passive tension by about half, but not that against KCl-induced tone. Moreover, the combination failed to enhance inhibition by charybdotoxin against KCl-induced tone. We conclude that cAMP and cGMP each play a minor role in β-adrenergic receptor-mediated relaxation against passive tension, and calcium-dependent potassium channels play a minor role against active tension.
Footnotes
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This work was supported in part by a grant from the Deutsche Forschungsgemeinschaft (Mi 294/7-1).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.104.077768.
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ABBREVIATIONS: ODQ, 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one; H89, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide 2 HCl; H7, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine 2 HCl; Rp-cAMPS, Rp-adenosine 3′,5′-cyclic monophosphorothioate; l-NNA, Nω-nitro-l-arginine; SQ 22,536, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine; PKA, protein kinase A; NO, nitric oxide; BKCa, large-conductance calcium-activated K+ channels.
- Received September 13, 2004.
- Accepted December 1, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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