8-Bromo-cAMP decreases the Ca2+ sensitivity of airway smooth muscle contraction through a mechanism distinct from inhibition of Rho-kinase.
To clarify whether cyclic AMP (cAMP)/cAMP-dependent protein kinase (PKA) activation and Rho-kinase inhibition share a common mechanism to decrease the Ca2+ sensitivity of airway smooth muscle contraction, we examined the effects of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), a stable cAMP analog, and (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide dihydrochloride, monohydrate (Y-27632), a Rho-kinase inhibitor, on carbachol (CCh)-, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS)-, 4beta-phorbol 12,13-dibutyrate (PDBu)-, and leukotriene D4 (LTD4)-induced Ca2+ sensitization in alpha-toxin-permeabilized rabbit tracheal and human bronchial smooth muscle. In rabbit trachea, CCh-induced smooth muscle contraction was inhibited by 8-BrcAMP and Y-27632 to a similar extent. However, GTPgammaS-induced smooth muscle contraction was resistant to 8-BrcAMP. In the presence of a saturating concentration of Y-27632, PDBu-induced smooth muscle contraction was completely reversed by 8-BrcAMP. Conversely, PDBu-induced smooth muscle contraction was resistant to Y-27632. In the presence of a saturating concentration of 8-BrcAMP, GTPgammaS-induced Ca2+ sensitization was also reversed by Y-27632. The 8-BrcAMP had no effect on the ATP-triggered contraction of tracheal smooth muscle that had been treated with calyculin A in rigor solutions. The 8-BrcAMP and Y-27632 additively accelerated the relaxation rate of PDBu- and GTPgammaS-treated smooth muscle under myosin light chain kinase-inhibited conditions. In human bronchus, LTD4-induced smooth muscle contraction was inhibited by both 8-BrcAMP and Y-27632. We conclude that cAMP/PKA-induced Ca2+ desensitization contains at least two mechanisms: 1) inhibition of the muscarinic receptor signaling upstream from Rho activation and 2) cAMP/PKA's preferential reversal of PKC-mediated Ca2+ sensitization in airway smooth muscle.
Endou
Katsuaki
K
Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, Maebashi, Japan.
Iizuka
Kunihiko
K
Yoshii
Akihiro
A
Tsukagoshi
Hideo
H
Ishizuka
Tamotsu
T
Dobashi
Kunio
K
Nakazawa
Tsugio
T
Mori
Masatomo
M
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000818:Animals; D001980:Bronchi / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D011817:Rabbits; D014132:Trachea / Q000187:drug effects / Q000502:physiology*; D054460:rho-Associated Kinases
D047908:Intracellular Signaling Peptides and Proteins; D015124:8-Bromo Cyclic Adenosine Monophosphate; D015240:Phorbol 12,13-Dibutyrate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002217:Carbachol; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D002118:Calcium