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This Article Full Text Full Text (PDF) All Versions of this Article: 288/6/H2887    most recent 00320.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (14) Citing Articles via Google Scholar Google Scholar Articles by Akar, F. G. Articles by Tomaselli, G. F. Search for Related Content PubMed PubMed Citation Articles by Akar, F. G. Articles by Tomaselli, G. F.

Molecular mechanisms underlying K⁺ current downregulation in canine tachycardia-induced heart failure

Institute of Molecular Cardiobiology, Division of Cardiology, School of Medicine, Johns Hopkins University, Baltimore, Maryland

Submitted 30 March 2004 ; accepted in final form 21 January 2005

Heart failure (HF) is characterized by marked prolongation of action potential duration and reduction in cellular repolarization reserve. These changes are caused in large part by HF-induced K⁺ current downregulation. Molecular mechanisms underlying these changes remain unclear. We determined whether downregulation of K⁺ currents in a canine model of tachycardia-induced HF is caused by altered expression of underlying K⁺ channel - and -subunits encoding these currents. K⁺ channel subunit expression was quantified in normal and failing dogs at the mRNA and protein levels in epicardial (Epi), midmyocardial (Mid), and endocardial (Endo) layers of left ventricle. Analysis of mRNA and protein levels of candidate genes encoding the transient outward K⁺ current (I_to) revealed marked reductions in canine cKv4.3 expression in HF in Epi (44% mRNA, 39% protein), Mid (52% mRNA, 34% protein), and Endo (49% mRNA, 73% protein) layers and a paradoxical enhancement (41% Epi, 97% Mid, 113% Endo) in cKv1.4 protein levels, without significant changes in Kv channel-interacting protein cKChIP2 expression. Expression of cKir2.1, the gene underlying inward rectifier K⁺ current (I_K1), was unaffected by HF at mRNA and protein levels despite significant reduction in I_K1, whereas canine ether-à-go-go-related gene (cERG), which encodes the rapidly activating component of the delayed rectifier current (I_K), exhibited increased protein expression. HF was not accompanied by significant changes in cKvLQT1 or cMinK mRNA and protein levels. These data indicate that 1) downregulation of I_to in HF is associated with decreased cKv4.3 and not cKv1.4 or cKChIP2, and 2) alterations in both the rapidly activating and slowly activating components of I_K as well as I_K1 in nonischemic dilated cardiomyopathy are not caused by changes in either transcript or immunoreactive protein levels of relevant channel subunits, which suggests posttranslational modification of these currents by HF.

potassium current; inward rectifier; transient outward; myocardial infarction

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