title: Overexpression of wild-type Galpha(i)-2 suppresses beta-adrenergic signaling in cardiac myocytes.
abstract: The role of Galpha(i)-2 overexpression in desensitization of beta-adrenergic signaling in heart failure is controversial. An adenovirus-based approach was used to investigate whether overexpression of Galpha(i)-2 impairs beta-adrenergic stimulation of adenylyl cyclase (AC) activity and cAMP levels in neonatal rat cardiac myocytes (NRCM) and cell shortening of adult rat ventricular myocytes (ARVM). Infection of NRCM with Ad5Galpha(i)-2 increased Galpha(i)-2 by 50-600% in a virus dose-dependent manner. Overexpression was paralleled by suppression of GTP- and isoprenaline-stimulated AC by 10-72% (P<0.001) in a PTX-sensitive manner. Isoprenaline-stimulated shortening of Ad5Galpha(i)-2-infected ARVM was attenuated by 34% (P<0.01). Ad5Galpha(i)-2/GFP (Galpha(i)-2, green fluorescent protein; bicistronic) was constructed to monitor transfection homogeneity and target Galpha(i)-2 overexpression to levels found in heart failure. At Galpha(i)-2 levels of 93% above control, isoprenaline-stimulated AC activity and cAMP levels were reduced by 17% and 40% (P<0.02), respectively. Beta1- and beta2-adrenergic stimulation was reduced similarly. Our results suggest that (a) the Galpha(i)-2 system exhibits tonic inhibition of stimulated AC in cardiac myocytes, (b) Galpha(i)-2-mediated inhibition is concentration-dependent and occurs at Galpha(i)-2 levels seen in heart failure, and (c) Galpha(i)-2-mediated inhibition affects both beta1- and beta2-adrenergic stimulation of AC. The data argue for an important, independent role of the Galpha(i)-2 increase in heart failure.
authors.affiliation: Institute of Pharmacology and Toxicology, Friedrich Alexander University Erlangen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rau
authors.forename: Monika
authors.initials: M
authors.lastname: Nose
authors.forename: Ute
authors.initials: U
authors.lastname: Remmers
authors.forename: Joachim
authors.initials: J
authors.lastname: Weil
authors.forename: Astrid
authors.initials: A
authors.lastname: Weissmüller
authors.forename: Kerry
authors.initials: K
authors.lastname: Davia
authors.forename: Sian
authors.initials: S
authors.lastname: Harding
authors.forename: Karsten
authors.initials: K
authors.lastname: Peppel
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koch
authors.forename: Thomas
authors.initials: T
authors.lastname: Eschenhagen
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D005822:Genetic Vectors; D007545:Isoproterenol / Q000037:antagonists & inhibitors*; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction
chemical_list: D000318:Adrenergic beta-Agonists; D011518:Proto-Oncogene Proteins; D000242:Cyclic AMP; D037342:Pertussis Toxin; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C498017:Gnai2 protein, rat; D000262:Adenylyl Cyclases; D007545:Isoproterenol