title: β-Agonist-mediated relaxation of airway smooth muscle is protein kinase A-dependent.
abstract: Inhaled β-agonists are effective at reversing bronchoconstriction in asthma, but the mechanism by which they exert this effect is unclear and controversial. PKA is the historically accepted effector, although this assumption is made on the basis of associative and not direct evidence. Recent studies have asserted that exchange protein activated by cAMP (Epac), not PKA, mediates the relaxation of airway smooth muscle (ASM) observed with β-agonist treatment. This study aims to clarify the role of PKA in the prorelaxant effects of β-agonists on ASM. Inhibition of PKA activity via expression of the PKI and RevAB peptides results in increased β-agonist-mediated cAMP release, abolishes the inhibitory effect of isoproterenol on histamine-induced intracellular calcium flux, and significantly attenuates histamine-stimulated MLC-20 phosphorylation. Analyses of ASM cell and tissue contraction demonstrate that PKA inhibition eliminates most, if not all, β-agonist-mediated relaxation of contracted smooth muscle. Conversely, Epac knockdown had no effect on the regulation of contraction or procontractile signaling by isoproterenol. These findings suggest that PKA, not Epac, is the predominant and physiologically relevant effector through which β-agonists exert their relaxant effects.
authors: Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors: Sarah J
authors: SJ
authors: Morgan
authors: Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors: Deepak A
authors: DA
authors: Deshpande
authors: Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors: Brian C
authors: BC
authors: Tiegs
authors: Department of Internal Medicine, Wake Forest University Health Sciences, Winston-Salem, North Carolina 27106.
authors: Anna M
authors: AM
authors: Misior
authors: Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors: Huandong
authors: H
authors: Yan
authors: Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors: Alena V
authors: AV
authors: Hershfeld
authors: Department of Pharmacology, College of Medicine and Center for Lung Biology, University of South Alabama, Mobile, Alabama 36688.
authors: Thomas C
authors: TC
authors: Rich
authors: Department of Medicine, Pulmonary, Allergy, and Critical Care Division, Airways Biology Initiative, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104.
authors: Reynold A
authors: RA
authors: Panettieri
authors: Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland 21205, and.
authors: Steven S
authors: SS
authors: An
authors: Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201,; Department of Medicine, Division of Pulmonary and Critical Care Medicine, Center for Translational Medicine, Jane and Leonard Korman Lung Center, Thomas Jefferson University, Philadelphia, Pennsylvania 19107. Electronic address: Raymond.Penn@jefferson.edu.
authors: Raymond B
authors: RB
authors: Penn
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D012137:Respiratory System / Q000166:cytology / Q000378:metabolism*
chemical_list: D000318:Adrenergic beta-Agonists; D020662:Guanine Nucleotide Exchange Factors; C116122:RAPGEF3 protein, human; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol
keywords: Adrenergic Receptor; Asthma; G Protein-coupled Receptor (GPCR); Protein Kinase A (PKA); Smooth Muscle