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The RyR2-P2328S mutation downregulates Nav1.5 producing arrhythmic substrate in murine ventricles.

Published version
Peer-reviewed

Repository DOI


Type

Article

Change log

Authors

Ning, Feifei 
Luo, Ling 
Ahmad, Shiraz 
Valli, Haseeb 
Jeevaratnam, Kamalan 

Abstract

Catecholaminergic polymorphic ventricular tachycardia (CPVT) predisposes to ventricular arrhythmia due to altered Ca(2+) homeostasis and can arise from ryanodine receptor (RyR2) mutations including RyR2-P2328S. Previous reports established that homozygotic murine RyR2-P2328S (RyR2 (S/S)) hearts show an atrial arrhythmic phenotype associated with reduced action potential (AP) conduction velocity and sodium channel (Nav1.5) expression. We now relate ventricular arrhythmogenicity and slowed AP conduction in RyR2 (S/S) hearts to connexin-43 (Cx43) and Nav1.5 expression and Na(+) current (I Na). Stimulation protocols applying extrasystolic S2 stimulation following 8 Hz S1 pacing at progressively decremented S1S2 intervals confirmed an arrhythmic tendency despite unchanged ventricular effective refractory periods (VERPs) in Langendorff-perfused RyR2 (S/S) hearts. Dynamic pacing imposing S1 stimuli then demonstrated that progressive reductions of basic cycle lengths (BCLs) produced greater reductions in conduction velocity at equivalent BCLs and diastolic intervals in RyR2 (S/S) than WT, but comparable changes in AP durations (APD90) and their alternans. Western blot analyses demonstrated that Cx43 protein expression in whole ventricles was similar, but Nav1.5 expression in both whole tissue and membrane fractions were significantly reduced in RyR2 (S/S) compared to wild-type (WT). Loose patch-clamp studies similarly demonstrated reduced I Na in RyR2 (S/S) ventricles. We thus attribute arrhythmogenesis in RyR2 (S/S) ventricles resulting from arrhythmic substrate produced by reduced conduction velocity to downregulated Nav1.5 reducing I Na, despite normal determinants of repolarization and passive conduction. The measured changes were quantitatively compatible with earlier predictions of linear relationships between conduction velocity and the peak I Na of the AP but nonlinear relationships between peak I Na and maximum Na(+) permeability.

Description

Keywords

Arrhythmogenicity, CPVT, Ca2+ homeostasis, Conduction velocity, Nav1.5, RyR2, Action Potentials, Animals, Arrhythmias, Cardiac, Connexin 43, Down-Regulation, Female, Heart Ventricles, Male, Mice, Mutation, Missense, NAV1.5 Voltage-Gated Sodium Channel, Ryanodine Receptor Calcium Release Channel, Ventricular Function

Journal Title

Pflugers Arch

Conference Name

Journal ISSN

0031-6768
1432-2013

Volume Title

468

Publisher

Springer Science and Business Media LLC
Sponsorship
Royal Society (1562)
Medical Research Council (MR/M001288/1)
Wellcome Trust (105727/Z/14/Z)
British Heart Foundation (None)
This work was supported by Royal Society / National Science Foundation of China International Joint Project Grant (JP100994/ No.81211130599) (JAF and AM), Issac Newton Trust/ Wellcome Trust ISSF/ University of Cambridge Joint Research Grants Scheme (JAF) and by the Wellcome Trust and Medical Research Council (CLH).