title: Mechanisms underlying rate-dependent remodeling of transient outward potassium current in canine ventricular myocytes.
abstract: Transient outward K+ current (I to) downregulation following sustained tachycardia in vivo is usually attributed to tachycardiomyopathy. This study assessed potential direct rate regulation of cardiac I(to) and underlying mechanisms. Cultured adult canine left ventricular cardiomyocytes (37 degrees C) were paced continuously at 1 or 3 Hz for 24 hours. I to was recorded with whole-cell patch clamp. The 3-Hz pacing reduced I to by 44% (P<0.01). Kv4.3 mRNA and protein expression were significantly reduced (by approximately 30% and approximately 40%, respectively) in 3-Hz paced cells relative to 1-Hz cells, but KChIP2 expression was unchanged. Prevention of Ca2+ loading with nimodipine or calmodulin inhibition with W-7, A-7, or W-13 eliminated 3-Hz pacing-induced I to downregulation, whereas downregulation was preserved in the presence of valsartan. Inhibition of Ca2+/calmodulin-dependent protein kinase (CaMK)II with KN93, or calcineurin with cyclosporin A, also prevented I to downregulation. CaMKII-mediated phospholamban phosphorylation at threonine 17 was increased in 3-Hz paced cells, compatible with enhanced CaMKII activity, with functional significance suggested by acceleration of the Ca2+i transient decay time constant (Indo 1-acetoxymethyl ester microfluorescence). Total phospholamban expression was unchanged, as was expression of Na+/Ca2+ exchange and sarcoplasmic reticulum Ca2+-ATPase proteins. Nuclear localization of the calcineurin-regulated nuclear factor of activated T cells (NFAT)c3 was increased in 3-Hz paced cells compared to 1-Hz (immunohistochemistry, immunoblot). INCA-6 inhibition of NFAT prevented I to reduction in 3-Hz paced cells. Calcineurin activity increased after 6 hours of 3-Hz pacing. CaMKII inhibition prevented calcineurin activation and NFATc3 nuclear translocation with 3-Hz pacing. We conclude that tachycardia downregulates I to expression, with the Ca2+/calmodulin-dependent CaMKII and calcineurin/NFAT systems playing key Ca2+-sensing and signal-transducing roles in rate-dependent I to control.
authors: Department of Medicine, Montreal Heart Institute and Université de Montréal, Montreal, Quebec, Canada.
authors: Ling
authors: L
authors: Xiao
authors: Pierre
authors: P
authors: Coutu
authors: Louis R
authors: LR
authors: Villeneuve
authors: Artavazd
authors: A
authors: Tadevosyan
authors: Ange
authors: A
authors: Maguy
authors: Sabrina
authors: S
authors: Le Bouter
authors: Bruce G
authors: BG
authors: Allen
authors: Stanley
authors: S
authors: Nattel
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002135:Calcium-Binding Proteins / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D004285:Dogs; D006352:Heart Ventricles; D017136:Ion Transport / Q000187:drug effects; D051605:Kv Channel-Interacting Proteins / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism*; D050778:NFATC Transcription Factors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D051672:Shal Potassium Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism; D013610:Tachycardia / Q000378:metabolism*; D000099211:Phospholamban
chemical_list: D019703:Calcineurin; D002118:Calcium; D002121:Calcium Channel Blockers; D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D051605:Kv Channel-Interacting Proteins; D050778:NFATC Transcription Factors; D047428:Protein Kinase Inhibitors; D051672:Shal Potassium Channels; D019831:Sodium-Calcium Exchanger; D000099211:Phospholamban; C445503:transcription factor NF-AT c3