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Ionic Mechanisms of Impulse Propagation Failure in the FHF2-Deficient Heart


Park, David S; Shekhar, Akshay; Santucci, John; Redel-Traub, Gabriel; Solinas, Sergio; Mintz, Shana; Lin, Xianming; Chang, Ernest Whanwook; Narke, Deven; Xia, Yuhe; Goldfarb, Mitchell; Fishman, Glenn I (2020). Ionic Mechanisms of Impulse Propagation Failure in the FHF2-Deficient Heart. Circulation Research, 127(12):1536-1548.

Abstract

Rationale:

FHFs (fibroblast growth factor homologous factors) are key regulators of sodium channel (NaV) inactivation. Mutations in these critical proteins have been implicated in human diseases including Brugada syndrome, idiopathic ventricular arrhythmias, and epileptic encephalopathy. The underlying ionic mechanisms by which reduced Nav availability in Fhf2 knockout (Fhf2KO) mice predisposes to abnormal excitability at the tissue level are not well defined.
Objective:

Using animal models and theoretical multicellular linear strands, we examined how FHF2 orchestrates the interdependency of sodium, calcium, and gap junctional conductances to safeguard cardiac conduction.
Methods and Results:

Fhf2KO mice were challenged by reducing calcium conductance (gCaV) using verapamil or by reducing gap junctional conductance (Gj) using carbenoxolone or by backcrossing into a cardiomyocyte-specific Cx43 (connexin 43) heterozygous background. All conditions produced conduction block in Fhf2KO mice, with Fhf2 wild-type (Fhf2WT) mice showing normal impulse propagation. To explore the ionic mechanisms of block in Fhf2KO hearts, multicellular linear strand models incorporating FHF2-deficient Nav inactivation properties were constructed and faithfully recapitulated conduction abnormalities seen in mutant hearts. The mechanisms of conduction block in mutant strands with reduced gCaV or diminished Gj are very different. Enhanced Nav inactivation due to FHF2 deficiency shifts dependence onto calcium current (ICa) to sustain electrotonic driving force, axial current flow, and action potential (AP) generation from cell-to-cell. In the setting of diminished Gj, slower charging time from upstream cells conspires with accelerated Nav inactivation in mutant strands to prevent sufficient downstream cell charging for AP propagation.
Conclusions:

FHF2-dependent effects on Nav inactivation ensure adequate sodium current (INa) reserve to safeguard against numerous threats to reliable cardiac impulse propagation.

Abstract

Rationale:

FHFs (fibroblast growth factor homologous factors) are key regulators of sodium channel (NaV) inactivation. Mutations in these critical proteins have been implicated in human diseases including Brugada syndrome, idiopathic ventricular arrhythmias, and epileptic encephalopathy. The underlying ionic mechanisms by which reduced Nav availability in Fhf2 knockout (Fhf2KO) mice predisposes to abnormal excitability at the tissue level are not well defined.
Objective:

Using animal models and theoretical multicellular linear strands, we examined how FHF2 orchestrates the interdependency of sodium, calcium, and gap junctional conductances to safeguard cardiac conduction.
Methods and Results:

Fhf2KO mice were challenged by reducing calcium conductance (gCaV) using verapamil or by reducing gap junctional conductance (Gj) using carbenoxolone or by backcrossing into a cardiomyocyte-specific Cx43 (connexin 43) heterozygous background. All conditions produced conduction block in Fhf2KO mice, with Fhf2 wild-type (Fhf2WT) mice showing normal impulse propagation. To explore the ionic mechanisms of block in Fhf2KO hearts, multicellular linear strand models incorporating FHF2-deficient Nav inactivation properties were constructed and faithfully recapitulated conduction abnormalities seen in mutant hearts. The mechanisms of conduction block in mutant strands with reduced gCaV or diminished Gj are very different. Enhanced Nav inactivation due to FHF2 deficiency shifts dependence onto calcium current (ICa) to sustain electrotonic driving force, axial current flow, and action potential (AP) generation from cell-to-cell. In the setting of diminished Gj, slower charging time from upstream cells conspires with accelerated Nav inactivation in mutant strands to prevent sufficient downstream cell charging for AP propagation.
Conclusions:

FHF2-dependent effects on Nav inactivation ensure adequate sodium current (INa) reserve to safeguard against numerous threats to reliable cardiac impulse propagation.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Neuroinformatics
Dewey Decimal Classification:570 Life sciences; biology
Scopus Subject Areas:Life Sciences > Physiology
Health Sciences > Cardiology and Cardiovascular Medicine
Uncontrolled Keywords:Physiology, Cardiology and Cardiovascular Medicine
Language:English
Date:4 December 2020
Deposited On:15 Feb 2021 13:31
Last Modified:16 Feb 2021 21:01
Publisher:Lippincott Williams & Wilkins
ISSN:0009-7330
OA Status:Closed
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1161/circresaha.120.317349

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