Cyclic nucleotide-dependent phosphodiesterases (PDEI) inhibition by muscarinic antagonists in bovine tracheal smooth muscle.
In bovine tracheal smooth muscle (TSM) strips, muscarinic antagonists (atropine, 4-DAMP, AFDX-116 and methoctramine) were able to increase simultaneously and a similar fashion the intracellular levels of cyclic nucleotides, with a cAMP/cGMP ratio higher than 2.0. These original pharmacological responses were time-and dose-dependent, exhibiting maximal values at 15 min, with a pEC(50) of 7.4 +/- 0.2 for atropine and 4-DAMP. These effects on cAMP and cGMP levels were similar to the ones obtained with isobutyl-methylxantine (IBMX, 10 microM), a non-selective cyclic nucleotide phosphodiesterase (PDE) inhibitor, suggesting the involvement of PDEs in these muscarinic antagonist responses. Neither, rolipram (10 microM), a specific PDEIV inhibitor, nor zaprinast (10 microM), a PDEV inhibitor, exhibited this "atropine-like" responses. Instead, atropine enhanced the increments of cAMP levels induced by rolipram and cGMP levels by zaprinast. However, vinpocetine (20 microM), a non-calmodulin dependent PDEIC inhibitor was able to mimic these muscarinic antagonist responses in intact smooth muscle strips. In addition, in cell free systems, muscarinic antagonists inhibited the membrane-bound PDEIC activity whereas soluble (cytosol) PDEIC activity was not affected by these muscarinic drugs. These results indicate that muscarinic antagonists acting possibly as inverse agonists on M(2)/M(3)mAChRs anchored to sarcolemma membranes can initiate a new signal transducing cascade leading to the PDEIC inhibition, which produced a simultaneous rise in both cAMP and cGMP intracellular levels in tracheal smooth muscle.
Sección de Biomembranas y Cátedra de Patología General y Fisiopatología, Instituto de Medicina Experimental, Facultad de Medicina, Universidad Central de Venezuela, Caracas, Venezuela.
Lérida
L
Guerra de González
Ramona
R
González de Alfonzo
Itala
I
Lippo de Bécemberg
Marcelo J
MJ
Alfonzo
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002417:Cattle; D002474:Cell-Free System; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D011688:Purinones / Q000494:pharmacology; D020889:Rolipram / Q000494:pharmacology; D014132:Trachea / Q000166:cytology; D014748:Vinca Alkaloids / Q000494:pharmacology
D018727:Muscarinic Antagonists; D010726:Phosphodiesterase Inhibitors; D011688:Purinones; D014748:Vinca Alkaloids; C013983:vinpocetine; D001285:Atropine; D000242:Cyclic AMP; D010727:Phosphoric Diester Hydrolases; C011145:zaprinast; D006152:Cyclic GMP; D020889:Rolipram