title: Cardiac-restricted expression of the carboxyl-terminal fragment of GRK3 Uncovers Distinct Functions of GRK3 in regulation of cardiac contractility and growth: GRK3 controls cardiac alpha1-adrenergic receptor responsiveness.
abstract: G protein-coupled receptor kinase-2 and -3 (GRK2 and GRK3) in cardiac myocytes catalyze phosphorylation and desensitization of different G protein-coupled receptors through specificity controlled by their carboxyl-terminal pleckstrin homology domain. Although GRK2 has been extensively investigated, the function of cardiac GRK3 remains unknown. Thus, in this study cardiac function of GRK3 was investigated in transgenic (Tg) mice with cardiac-restricted expression of a competitive inhibitor of GRK3, i.e. the carboxyl-terminal plasma membrane targeting domain of GRK3 (GRK3ct). Cardiac myocytes from Tg-GRK3ct mice displayed significantly enhanced agonist-stimulated alpha(1)-adrenergic receptor-mediated activation of ERK1/2 versus cardiac myocytes from nontransgenic littermate control (NLC) mice consistent with inhibition of GRK3. Tg-GRK3ct mice did not display alterations of cardiac mass or left ventricular dimensions compared with NLC mice. Tail-cuff plethysmography of 3- and 9-month-old mice revealed elevated systolic blood pressure in Tg-GRK3ct mice versus control mice (3-month-old mice, 136.8 +/- 3.6 versus 118.3 +/- 4.7 mm Hg, p < 0.001), an observation confirmed by radiotelemetric recording of blood pressure of conscious, unrestrained mice. Simultaneous recording of left ventricular pressure and volume in vivo by miniaturized conductance micromanometry revealed increased systolic performance with significantly higher stroke volume and stroke work in Tg-GRK3ct mice than in NLC mice. This phenotype was corroborated in electrically paced ex vivo perfused working hearts. However, analysis of left ventricular function ex vivo as a function of increasing filling pressure disclosed significantly reduced (dP/dt)(min) and prolonged time constant of relaxation (tau) in Tg-GRK3ct hearts at elevated supraphysiological filling pressure compared with control hearts. Thus, inhibition of GRK3 apparently reduces tolerance to elevation of preload. In conclusion, inhibition of cardiac GRK3 causes hypertension because of hyperkinetic myocardium and increased cardiac output relying at least partially on cardiac myocyte alpha(1)-adrenergic receptor hyper-responsiveness. The reduced tolerance to elevation of preload may cause impaired ability to withstand pathophysiological mechanisms of heart failure.
authors.affiliation: Institute for Surgical Research, University of Oslo and Rikshospitalet-Radiumhospitalet Medical Center, Oslo N-0027, Norway.
authors.forename: Leif Erik
authors.initials: LE
authors.lastname: Vinge
authors.forename: Thomas G
authors.initials: TG
authors.lastname: von Lueder
authors.forename: Ellen
authors.initials: E
authors.lastname: Aasum
authors.forename: Eirik
authors.initials: E
authors.lastname: Qvigstad
authors.forename: Jørgen A
authors.initials: JA
authors.lastname: Gravning
authors.forename: Ole-Jakob
authors.initials: OJ
authors.lastname: How
authors.forename: Thor
authors.initials: T
authors.lastname: Edvardsen
authors.forename: Reidar
authors.initials: R
authors.lastname: Bjørnerheim
authors.forename: M Shakil
authors.initials: MS
authors.lastname: Ahmed
authors.forename: Birthe W
authors.initials: BW
authors.lastname: Mikkelsen
authors.forename: Erik
authors.initials: E
authors.lastname: Oie
authors.forename: Toril
authors.initials: T
authors.lastname: Attramadal
authors.forename: Tor
authors.initials: T
authors.lastname: Skomedal
authors.forename: Otto A
authors.initials: OA
authors.lastname: Smiseth
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koch
authors.forename: Terje S
authors.initials: TS
authors.lastname: Larsen
authors.forename: Håvard
authors.initials: H
authors.lastname: Attramadal
mesh_terms: D000818:Animals; D001794:Blood Pressure; D002478:Cells, Cultured; D054770:G-Protein-Coupled Receptor Kinase 3 / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation; D006352:Heart Ventricles / Q000473:pathology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D010641:Phenotype; D010991:Plethysmography; D017434:Protein Structure, Tertiary; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*
chemical_list: D018340:Receptors, Adrenergic, alpha-1; D054770:G-Protein-Coupled Receptor Kinase 3; C517850:GRK3 protein, mouse