title: Exchange protein directly activated by cAMP mediates slow delayed-rectifier current remodeling by sustained β-adrenergic activation in guinea pig hearts.
abstract: BACKGROUND
  β-Adrenoceptor activation contributes to sudden death risk in heart failure. Chronic β-adrenergic stimulation, as occurs in patients with heart failure, causes potentially arrhythmogenic reductions in slow delayed-rectifier K(+) current (IKs).
  
  
  OBJECTIVE
  To assess the molecular mechanisms of IKs downregulation caused by chronic β-adrenergic activation, particularly the role of exchange protein directly activated by cAMP (Epac).
  
  
  RESULTS
  Isolated guinea pig left ventricular cardiomyocytes were incubated in primary culture and exposed to isoproterenol (1 μmol/L) or vehicle for 30 hours. Sustained isoproterenol exposure decreased IKs density (whole cell patch clamp) by 58% (P<0.0001), with corresponding decreases in potassium voltage-gated channel subfamily E member 1 (KCNE1) mRNA and membrane protein expression (by 45% and 51%, respectively). Potassium voltage-gated channel, KQT-like subfamily, member 1 (KCNQ1) mRNA expression was unchanged. The β1-adrenoceptor antagonist 1-[2-((3-Carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol dihydrochloride (CGP-20712A) prevented isoproterenol-induced IKs downregulation, whereas the β2-antagonist ICI-118551 had no effect. The selective Epac activator 8-pCPT-2'-O-Me-cAMP decreased IKs density to an extent similar to isoproterenol exposure, and adenoviral-mediated knockdown of Epac1 prevented isoproterenol-induced IKs/KCNE1 downregulation. In contrast, protein kinase A inhibition with a cell-permeable highly selective peptide blocker did not affect IKs downregulation. 1,2-Bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetate-AM acetoxymethyl ester (BAPTA-AM), cyclosporine, and inhibitor of nuclear factor of activated T cell (NFAT)-calcineurin association-6 (INCA6) prevented IKs reduction by isoproterenol and INCA6 suppressed isoproterenol-induced KCNE1 downregulation, consistent with signal-transduction via the Ca(2+)/calcineurin/NFAT pathway. Isoproterenol induced nuclear NFATc3/c4 translocation (immunofluorescence), which was suppressed by Epac1 knockdown. Chronic in vivo administration of isoproterenol to guinea pigs reduced IKs density and KCNE1 mRNA and protein expression while inducing cardiac dysfunction and action potential prolongation. Selective in vivo activation of Epac via sp-8-pCPT-2'-O-Me-cAMP infusion decreased IKs density and KCNE1 mRNA/protein expression.
  
  
  CONCLUSIONS
  Prolonged β1-adrenoceptor stimulation suppresses IKs by downregulating KCNE1 mRNA and protein via Epac-mediated Ca(2+)/calcineurin/NFAT signaling. These results provide new insights into the molecular basis of K(+) channel remodeling under sustained adrenergic stimulation.
authors: From the Department of Medicine, Research Center, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (M.A., X.-Y.Q., L.X., B.O., A.T., X.L., A.M., Y.S., J.-C.T., S.N.); and Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada (M.A., S.N.).
authors: Mona
authors: M
authors: Aflaki
authors: Xiao-Yan
authors: XY
authors: Qi
authors: Ling
authors: L
authors: Xiao
authors: Balazs
authors: B
authors: Ordog
authors: Artavazd
authors: A
authors: Tadevosyan
authors: Xiaobin
authors: X
authors: Luo
authors: Ange
authors: A
authors: Maguy
authors: Yanfen
authors: Y
authors: Shi
authors: Jean-Claude
authors: JC
authors: Tardif
authors: Stanley
authors: S
authors: Nattel
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000318:Adrenergic beta-Agonists / Q000633:toxicity*; D000818:Animals; D019703:Calcineurin / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D051668:Delayed Rectifier Potassium Channels / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D006168:Guinea Pigs; D017379:Hypertrophy, Left Ventricular / Q000209:etiology; D007093:Imidazoles / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology / Q000633:toxicity*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D011412:Propanolamines / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology; D018342:Receptors, Adrenergic, beta-1 / Q000187:drug effects / Q000502:physiology*; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology
chemical_list: C473217:8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate; D000318:Adrenergic beta-Agonists; D051668:Delayed Rectifier Potassium Channels; D020662:Guanine Nucleotide Exchange Factors; D007093:Imidazoles; D050778:NFATC Transcription Factors; D011412:Propanolamines; D034741:RNA, Small Interfering; D018342:Receptors, Adrenergic, beta-1; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D005576:Colforsin; C026777:ICI 118551; D004533:Egtazic Acid; C049763:CGP 20712A; D000242:Cyclic AMP; D019703:Calcineurin; D007545:Isoproterenol; D011188:Potassium; D002118:Calcium
keywords: arrhythmias, cardiac; calcineurin; heart failure; ion channels; β-adrenergic receptors