title: Inhibition of spontaneous beta 2-adrenergic activation rescues beta 1-adrenergic contractile response in cardiomyocytes overexpressing beta 2-adrenoceptor.
abstract: Cardiac-specific overexpression of the human beta(2)-adrenergic receptor (AR) in transgenic mice (TG4) enhances basal cardiac function due to ligand-independent spontaneous beta(2)-AR activation. However, agonist-mediated stimulation of either beta(1)-AR or beta(2)-AR fails to further enhance contractility in TG4 ventricular myocytes. Although the lack of beta(2)-AR response has been ascribed to an efficient coupling of the receptor to pertussis toxin-sensitive G(i) proteins in addition to G(s), the contractile response to beta(1)-AR stimulation by norepinephrine and an alpha(1)-adrenergic antagonist prazosin is not restored by pertussis toxin treatment despite a G(i) protein elevation of 1.7-fold in TG4 hearts. Since beta-adrenergic receptor kinase, betaARK1, activity remains unaltered, the unresponsiveness of beta(1)-AR is not caused by betaARK1-mediated receptor desensitization. In contrast, pre-incubation of cells with anti-adrenergic reagents such as muscarinic receptor agonist, carbachol (10(-5)m), or a beta(2)-AR inverse agonist, ICI 118,551 (5 x 10(-7)m), to abolish spontaneous beta(2)-AR signaling, both reduce the base-line cAMP and contractility and, surprisingly, restore the beta(1)-AR contractile response. The "rescued" contractile response is completely reversed by a beta(1)-AR antagonist, CGP 20712A. Furthermore, these results from the transgenic animals are corroborated by in vitro acute gene manipulation in cultured wild type adult mouse ventricular myocytes. Adenovirus-directed overexpression of the human beta(2)-AR results in elevated base-line cAMP and contraction associated with a marked attenuation of beta(1)-AR response; carbachol pretreatment fully revives the diminished beta(1)-AR contractile response. Thus, we conclude that constitutive beta(2)-AR activation induces a heterologous desensitization of beta(1)-ARs independent of betaARK1 and G(i) proteins; suppression of the constitutive beta(2)-AR signaling by either a beta(2)-AR inverse agonist or stimulation of the muscarinic receptor rescues the beta(1)-ARs from desensitization, permitting agonist-induced contractile response.
authors.affiliation: Laboratory of Cardiovascular Sciences, Gerontology Research Center, NIA, National Institutes of Health, Baltimore, Maryland 21224, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Zhang
authors.forename: H
authors.initials: H
authors.lastname: Cheng
authors.forename: Y Y
authors.initials: YY
authors.lastname: Zhou
authors.forename: D J
authors.initials: DJ
authors.lastname: Wang
authors.forename: W
authors.initials: W
authors.lastname: Zhu
authors.forename: B
authors.initials: B
authors.lastname: Ziman
authors.forename: H
authors.initials: H
authors.lastname: Spurgoen
authors.forename: R J
authors.initials: RJ
authors.lastname: Lefkowitz
authors.forename: E G
authors.initials: EG
authors.lastname: Lakatta
authors.forename: W J
authors.initials: WJ
authors.lastname: Koch
authors.forename: R P
authors.initials: RP
authors.lastname: Xiao
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D054769:G-Protein-Coupled Receptor Kinase 2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000502:physiology; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D006801:Humans; D051379:Mice; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology*; D009638:Norepinephrine / Q000494:pharmacology; D037342:Pertussis Toxin; D011224:Prazosin / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology*; D018342:Receptors, Adrenergic, beta-1 / Q000502:physiology*; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D000318:Adrenergic beta-Agonists; D011412:Propanolamines; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D011994:Recombinant Proteins; D010566:Virulence Factors, Bordetella; C026777:ICI 118551; D002217:Carbachol; D000242:Cyclic AMP; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; C496568:GRK2 protein, mouse; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; D009638:Norepinephrine; D011224:Prazosin