scholarly journals Flecainide Paradoxically Activates Cardiac Ryanodine Receptor Channels under Low Activity Conditions: A Potential Pro-Arrhythmic Action

Cells ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 2101
Author(s):  
Samantha C. Salvage ◽  
Esther M. Gallant ◽  
James A. Fraser ◽  
Christopher L.-H. Huang ◽  
Angela F. Dulhunty
Keyword(s):  
Atrial Fibrillation ◽  
Ryanodine Receptor ◽  
Polymorphic Ventricular Tachycardia ◽  
Sodium Currents ◽  
Wild Type ◽  
Open Probability ◽  
Active Channels ◽  
Separate Activation ◽  
Low Activity ◽  
Cardiac Ryanodine Receptor

Cardiac ryanodine receptor (RyR2) mutations are implicated in the potentially fatal catecholaminergic polymorphic ventricular tachycardia (CPVT) and in atrial fibrillation. CPVT has been successfully treated with flecainide monotherapy, with occasional notable exceptions. Reported actions of flecainide on cardiac sodium currents from mice carrying the pro-arrhythmic homozygotic RyR2-P2328S mutation prompted our explorations of the effects of flecainide on their RyR2 channels. Lipid bilayer electrophysiology techniques demonstrated a novel, paradoxical increase in RyR2 activity. Preceding flecainide exposure, channels were mildly activated by 1 mM luminal Ca2+ and 1 µM cytoplasmic Ca2+, with open probabilities (Po) of 0.03 ± 0.01 (wild type, WT) or 0.096 ± 0.024 (P2328S). Open probability (Po) increased within 0.5 to 3 min of exposure to 0.5 to 5.0 µM cytoplasmic flecainide, then declined with higher concentrations of flecainide. There were no such increases in a subset of high Po channels with Po ≥ 0.08, although Po then declined with ≥5 µM (WT) or ≥50 µM flecainide (P2328S). On average, channels with Po < 0.08 were significantly activated by 0.5 to 10 µM of flecainide (WT) or 0.5 to 50 µM of flecainide (P2328S). These results suggest that flecainide can bind to separate activation and inhibition sites on RyR2, with activation dominating in lower activity channels and inhibition dominating in more active channels.

scholarly journals The arrhythmogenic N53I variant subtly changes the structure and dynamics in the calmodulin N-terminal domain, altering its interaction with the cardiac ryanodine receptor

2020 ◽  
Vol 295 (22) ◽  
pp. 7620-7634
Author(s):  
Christian Holt ◽  
Louise Hamborg ◽  
Kelvin Lau ◽  
Malene Brohus ◽  
Anders Bundgaard Sørensen ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Ryanodine Receptor ◽  
Hydrophobic Surface ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Polymorphic Ventricular Tachycardia ◽  
Open Probability ◽  
Calmodulin Binding ◽  
Terminal Domain ◽  
Genes Encoding ◽  
Cardiac Ryanodine Receptor

Mutations in the genes encoding the highly conserved Ca2+-sensing protein calmodulin (CaM) cause severe cardiac arrhythmias, including catecholaminergic polymorphic ventricular tachycardia or long QT syndrome and sudden cardiac death. Most of the identified arrhythmogenic mutations reside in the C-terminal domain of CaM and mostly affect Ca2+-coordinating residues. One exception is the catecholaminergic polymorphic ventricular tachycardia–causing N53I substitution, which resides in the N-terminal domain (N-domain). It does not affect Ca2+ coordination and has only a minor impact on binding affinity toward Ca2+ and on other biophysical properties. Nevertheless, the N53I substitution dramatically affects CaM's ability to reduce the open probability of the cardiac ryanodine receptor (RyR2) while having no effect on the regulation of the plasmalemmal voltage-gated Ca2+ channel, Cav1.2. To gain more insight into the molecular disease mechanism of this mutant, we used NMR to investigate the structures and dynamics of both apo- and Ca2+-bound CaM-N53I in solution. We also solved the crystal structures of WT and N53I CaM in complex with the primary calmodulin-binding domain (CaMBD2) from RyR2 at 1.84–2.13 Å resolutions. We found that all structures of the arrhythmogenic CaM-N53I variant are highly similar to those of WT CaM. However, we noted that the N53I substitution exposes an additional hydrophobic surface and that the intramolecular dynamics of the protein are significantly altered such that they destabilize the CaM N-domain. We conclude that the N53I-induced changes alter the interaction of the CaM N-domain with RyR2 and thereby likely cause the arrhythmogenic phenotype of this mutation.

Abstract 944: Tight Binding Of Calmodulin To The Cardiac Ryanodine Receptor May Reduce The Spontaneous Ca 2+ Release Events Induced By Mutation-linked, Defective Inter-domain Interaction

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Xiaojuan Xu ◽  
Masafumi Yano ◽  
Makoto Ohno ◽  
Hitoshi Uchinoumi ◽  
Hiroki Tateishi ◽  
...  
Keyword(s):  
Ryanodine Receptor ◽  
Release Kinetics ◽  
Arrhythmogenic Right Ventricular Cardiomyopathy ◽  
Critical Role ◽  
Polymorphic Ventricular Tachycardia ◽  
Fluorescence Labeling ◽  
Domain Interaction ◽  
Human Mutation ◽  
Domain Peptide ◽  
Cardiac Ryanodine Receptor

Interaction between N-terminal 1– 600 and central domains 2000 –2500 of ryanodine receptor (RyR2), where many mutations have been found in patients with arrhythmogenic right ventricular cardiomyopathy type 2 (ARVC2) or catecholaminergic polymorphic ventricular tachycardia (CPVT), was recently found to play a critical role in channel regulation. Using the domain peptide approach, here, we investigated the role of calmodulin (CaM), one of the accessory proteins of the cardiac ryanodine receptor (RyR2), on Ca 2+ release kinetics. Sarcoplasmic reticulum (SR) vesicles were isolated from dog LV muscles (n=4), then RyR2 was fluorescently labeled with methylcoumarin acetate (MCA) using DP 163–195 , which harbors a human mutation site in ARVC (R176Q), as a site-directing carrier. DP 163–195 mediated a specific MCA fluorescence labeling of central domain (60Kd) of RyR2. Addition of DP 163–195 to the MCA-labeled SR competitively induced the domain unzipping between N-terminal and central domains, as evidenced by an increased accessibility of the bound MCA to a large-size fluorescence quencher. In saponin-permeabilized cardiomyocytes, the addition of DP 163–195 markedly increased the frequency of Ca 2+ sparks (SpF; s −1 ·100μm −1 :13.1±0.9, p<0.01), compared with normal cells (6.9±0.3). Addition of recombinant CaM (100nM), in the presence of KN-93 (CaMKII inhibitor), inhibited the DP 163–195 -induced increase in SpF (7.2±0.5, p<0.01). This effect of CaM was, however, abolished by co-addition of the antibody against the binding site of CaM within RyR2 (3583–3603) (SpF:12.9±0.7, p=ns), strongly suggesting that the binding of CaM to RyR2 corrects the abnormal Ca 2+ release induced by DP 163–195 . The mutation made in the domain peptide, mimicking the same human mutation in ARVC (R176Q) abolished all of the effects that would have been produced by DP 163–195 . In conclusion, the mutation-linked defective inter-domain interaction between N-terminal and central domains within RyR2 (viz. domain unzipping) may increase spontaneous Ca 2+ release, perhaps by weakening CaM-binding to RyR2. Restored binding of CaM to RyR2 may correct defective channel gating of the mutant RyR2.

scholarly journals Mutations of the Cardiac Ryanodine Receptor (RyR2) Gene in Familial Polymorphic Ventricular Tachycardia

Circulation ◽  
2001 ◽  
Vol 103 (4) ◽  
pp. 485-490 ◽  
Author(s):  
Päivi J. Laitinen ◽  
Kevin M. Brown ◽  
Kirsi Piippo ◽  
Heikki Swan ◽  
Joe M. Devaney ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Ryanodine Receptor ◽  
Polymorphic Ventricular Tachycardia ◽  
Cardiac Ryanodine Receptor

Role of ryanodine receptor mutations in cardiac pathology: more questions than answers?

2006 ◽  
Vol 34 (5) ◽  
pp. 913-918 ◽  
Author(s):  
N.L. Thomas ◽  
C.H. George ◽  
F.A. Lai
Keyword(s):  
Ryanodine Receptor ◽  
Ventricular Arrhythmias ◽  
Striated Muscle ◽  
Polymorphic Ventricular Tachycardia ◽  
Wild Type ◽  
Cell Interior ◽  
Cardiac Pathology ◽  
Physiological Processes ◽  
The Common

The RyR (ryanodine receptor) mediates rapid Ca2+ efflux from the ER (endoplasmic reticulum) and is responsible for triggering numerous Ca2+-activated physiological processes. The most studied RyR-mediated process is excitation–contraction coupling in striated muscle, where plasma membrane excitation is transmitted to the cell interior and results in Ca2+ efflux that triggers myocyte contraction. Recently, single-residue mutations in the cardiac RyR (RyR2) have been identified in families that exhibit CPVT (catecholaminergic polymorphic ventricular tachycardia), a condition in which physical or emotional stress can trigger severe tachyarrhythmias that can lead to sudden cardiac death. The RyR2 mutations in CPVT are clustered in the N- and C-terminal domains, as well as in a central domain. Further, a critical signalling role for dysfunctional RyR2 has also been implicated in the generation of arrhythmias in the common condition of HF (heart failure). We have prepared cardiac RyR2 plasmids with various CPVT mutations to enable expression and analysis of Ca2+ release mediated by the wild-type and mutated RyR2. These studies suggest that the mutational locus may be important in the mechanism of Ca2+ channel dysfunction. Understanding the causes of aberrant Ca2+ release via RyR2 may assist in the development of effective treatments for the ventricular arrhythmias that often leads to sudden death in HF and in CPVT.

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