title: Conditional knockout of Fgf13 in murine hearts increases arrhythmia susceptibility and reveals novel ion channel modulatory roles.
abstract: The intracellular fibroblast growth factors (iFGF/FHFs) bind directly to cardiac voltage gated Na+channels, and modulate their function. Mutations that affect iFGF/FHF-Na+channel interaction are associated with arrhythmia syndromes. Although suspected to modulate other ionic currents, such as Ca2+channels based on acute knockdown experiments in isolated cardiomyocytes, the in vivo consequences of iFGF/FHF gene ablation on cardiac electrical activity are still unknown. We generated inducible, cardiomyocyte-restricted Fgf13 knockout mice to determine the resultant effects of Fgf13 gene ablation. Patch clamp recordings from ventricular myocytes isolated from Fgf13 knockout mice showed a ~25% reduction in peak Na+channel current density and a hyperpolarizing shift in steady-state inactivation. Electrocardiograms on Fgf13 knockout mice showed a prolonged QRS duration. The Na+channel blocker flecainide further prolonged QRS duration and triggered ventricular tachyarrhythmias only in Fgf13 knockout mice, suggesting that arrhythmia vulnerability resulted, at least in part, from a loss of functioning Na+channels. Consistent with these effects on Na+channels, action potentials in Fgf13 knockout mice, compared to Cre control mice, exhibited slower upstrokes and reduced amplitude, but unexpectedly had longer durations. We investigated candidate sources of the prolonged action potential durations in myocytes from Fgf13 knockout mice and found a reduction of the transient outward K+current (Ito). Fgf13 knockout did not alter whole-cell protein levels of Kv4.2 and Kv4.3, the Itopore-forming subunits, but did decrease Kv4.2 and Kv4.3 at the sarcolemma. No changes were seen in the sustained outward K+current or voltage-gated Ca2+current, other candidate contributors to the increased action potential duration. These results implicate that FGF13 is a critical cardiac Na+channel modulator and Fgf13 knockout mice have increased arrhythmia susceptibility in the setting of Na+channel blockade. The unanticipated effect on Itorevealed new FGF13 properties and the unexpected lack of an effect on voltage-gated Ca2+channels highlight potential compensatory changes in vivo not readily revealed with acute Fgf13 knockdown in cultured cardiomyocytes.
authors.affiliation: Department of Pharmacology, Hebei Medical University, Shijiazhuang 050017, China; The Key Laboratory of Neural and Vascular Biology, Ministry of Education, China, Shijiazhuang, 050017, China; The Key Laboratory of New Drug Pharmacology and Toxicology, Hebei Province, Shijiazhuang 050017, China.
authors.forename: Xiangchong
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Pharmacology, Hebei Medical University, Shijiazhuang 050017, China; The Key Laboratory of Neural and Vascular Biology, Ministry of Education, China, Shijiazhuang, 050017, China; The Key Laboratory of New Drug Pharmacology and Toxicology, Hebei Province, Shijiazhuang 050017, China.
authors.forename: He
authors.initials: H
authors.lastname: Tang
authors.affiliation: Ion Channel Research Unit, Department of Medicine/Cardiology and Pharmacology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Eric Q
authors.initials: EQ
authors.lastname: Wei
authors.affiliation: Department of Pharmacology, Hebei Medical University, Shijiazhuang 050017, China; The Key Laboratory of Neural and Vascular Biology, Ministry of Education, China, Shijiazhuang, 050017, China; The Key Laboratory of New Drug Pharmacology and Toxicology, Hebei Province, Shijiazhuang 050017, China.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Cardiology, The Second Hospital of Hebei Medical University, Shijiazhuang 050000, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Yang
authors.affiliation: Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Pharmacology, Hebei Medical University, Shijiazhuang 050017, China; The Key Laboratory of Neural and Vascular Biology, Ministry of Education, China, Shijiazhuang, 050017, China; The Key Laboratory of New Drug Pharmacology and Toxicology, Hebei Province, Shijiazhuang 050017, China.
authors.forename: Yongjian
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Ion Channel Research Unit, Department of Medicine/Cardiology and Pharmacology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Pitt
authors.affiliation: Department of Pharmacology, Hebei Medical University, Shijiazhuang 050017, China; The Key Laboratory of Neural and Vascular Biology, Ministry of Education, China, Shijiazhuang, 050017, China; The Key Laboratory of New Drug Pharmacology and Toxicology, Hebei Province, Shijiazhuang 050017, China. Electronic address: zhanghl@hebmu.edu.cn.
authors.forename: Hailin
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology, Hebei Medical University, Shijiazhuang 050017, China; The Key Laboratory of Neural and Vascular Biology, Ministry of Education, China, Shijiazhuang, 050017, China; The Key Laboratory of New Drug Pharmacology and Toxicology, Hebei Province, Shijiazhuang 050017, China. Electronic address: wangchuan@hebmu.edu.cn.
authors.forename: Chuan
authors.initials: C
authors.lastname: Wang
mesh_terms: D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism* / Q000503:physiopathology; D004195:Disease Models, Animal; D004562:Electrocardiography; D005260:Female; D005346:Fibroblast Growth Factors / Q000172:deficiency*; D055786:Gene Knockout Techniques; D018390:Gene Targeting; D056426:Genetic Loci; D020022:Genetic Predisposition to Disease; D007473:Ion Channels / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology
chemical_list: D007473:Ion Channels; D015222:Sodium Channels; C108111:fibroblast growth factor 13; D005346:Fibroblast Growth Factors
keywords: Cardiac conditional knockout mice; FGF13; Fibroblast growth factor homologous factors; K(+) channel; Na(+) channel; Ventricular tachyarrhythmias