title: Desensitization of cardiac beta-adrenoceptor signaling with heart failure produced by myocardial infarction in the rat. Evidence for the role of Gi but not Gs or phosphorylating proteins.
abstract: This study examined mechanisms of beta-adrenergic (AR) desensitization in a myocardial infarction (MI) model of heart failure in the rat. Inotropic responses to isoproterenol (non-selective beta-AR agonist) and RO 363 (selective beta1-AR agonist), in left atria and left papillary muscle, were reduced by up to 65%, while chronotropic responses in right atria were unaffected. beta1- and beta2-AR density did not change after MI, suggesting that changes in beta-AR responsiveness are due to changes occurring downstream of the receptor. Inotropic and chronotropic responses to forskolin were not altered in right and left atria and left papillary muscle after MI, suggesting changes at the level of the G-proteins. Pertussis toxin treatment of animals restored inotropic responses to isoproterenol in left atria and left papillary muscle to levels seen in the sham group, indicating that inactivation of Gi-proteins improves inotropic function in MI rats, and that beta-ARs couple to Gi in cardiac failure. Expression of G-protein receptor kinase 2 (GRK2), beta-arrestin1 and the regulatory subunits of cAMPdPK (RI alpha and RII alpha), showed no change after MI. However the expression of Gi alpha2 was significantly increased in left ventricle (sham 0.888+/-0.140, MI 1. 759+/-0.352 P=0.026), right ventricle (sham 0.031+/-0.004, MI 0. 037+/-0.002 P=0.006) and atria (sham 0.107+/-0.006, MI 0.138+/-0.006 P=0.004), with no changes observed in the expression of Gs alpha. These results suggest that increases in Gi play an important role in the decreased beta-AR responsiveness in the rat model of MI.
authors.affiliation: Department of Pharmacology, Monash University, Wellington Road, Clayton, Victoria, 3168, Australia.
authors.forename: A R
authors.initials: AR
authors.lastname: Kompa
authors.forename: X H
authors.initials: XH
authors.lastname: Gu
authors.forename: B A
authors.initials: BA
authors.lastname: Evans
authors.forename: R J
authors.initials: RJ
authors.lastname: Summers
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D019390:Arrestins / Q000187:drug effects / Q000235:genetics; D001345:Autoradiography; D001794:Blood Pressure; D002118:Calcium / Q000494:pharmacology; D002396:Catechols / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000235:genetics; D054769:G-Protein-Coupled Receptor Kinase 2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism; D006333:Heart Failure / Q000378:metabolism*; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D007545:Isoproterenol / Q000494:pharmacology; D009203:Myocardial Infarction / Q000378:metabolism*; D009929:Organ Size; D037342:Pertussis Toxin; D010766:Phosphorylation; D011412:Propanolamines / Q000494:pharmacology; D012333:RNA, Messenger; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D051552:beta-Adrenergic Receptor Kinases; D000071557:beta-Arrestins
chemical_list: D000318:Adrenergic beta-Agonists; D019390:Arrestins; D002396:Catechols; D011412:Propanolamines; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D010566:Virulence Factors, Bordetella; D000071557:beta-Arrestins; D005576:Colforsin; C018420:Ro 363; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; C496569:Grk2 protein, rat; 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; D007545:Isoproterenol; D002118:Calcium