Abstract 795: Enhanced Sensitivity Of The Cardiac Ryanodine Receptor To Activation By Luminal Ca 2+ As A Primary Cause Of Catecholaminergic Polymorphic Ventricular Tachycardia

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Hitoshi Uchinoumi ◽  
Masafumi Yano ◽  
Makoto Ohno ◽  
Xiaojuan Xu ◽  
Hiroki Tateishi ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Ryanodine Receptor ◽  
Underlying Mechanism ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Polymorphic Ventricular Tachycardia ◽  
Enhanced Sensitivity ◽  
Histological Abnormality ◽  
Ryr2 Channel ◽  
The Relationship ◽  
Cardiac Ryanodine Receptor

Mutations in cardiac ryanodine receptor (RyR2) was found to be linked with catecholaminergic polymorphic ventricular tachycardia (CPVT). To study the underlying mechanism of CPVT, we developed knock-in mice harboring the Arg-to-Ser (R2474S) mutation. The RyR2 R2474S/+ knock-in (KI) mice revealed no structural or histological abnormality in hearts. Echocardiography showed no contractile or relaxation dysfunction at rest. In all KI mice (n=6), bidirectional ventricular tachycardia (VT) was observed during or after exercise with treadmill, but never observed in wild-type (WT) mice (n=6). In intact cardiomyocytes, the frequency of Ca 2+ sparks (SpF; s −1 ·100μm −1 ) was significantly increased in KI mice, but not in WT mice (at 2 mM [Ca 2+ ]; KI:6.4±0.7, WT:0.9±0.08, p<0.01). To investigate the sensitivity of the RyR2 channel to activation by luminal Ca 2+ {[Ca 2+ ] in sarcoplasmic reticulum (SR)}, we measured cytoplasmic [Ca 2+ ] ([Ca 2+ ] C ) and luminal [Ca 2+ ] ([Ca 2+ ] L ) simultaneously in saponin-permeabilized cardiomyocytes, using Rhod-2 and Fluo-5N AM as Ca 2+ indicators, respectively. When [Ca 2+ ] C was buffered at 100 nM (by 1 mM EGTA), the spontaneous Ca 2+ sparks were frequently observed both in KI and WT cardiomyocyts (SpF: KI:22.1±0.9, WT:22.0±0.8, p=ns). When we added thapsigargin (1 μM) to the cardiomyocytes under this condition ([Ca 2+ ] C =100 nM), both SpF and [Ca 2+ ] L gradually decreased due to a decrease in SR Ca 2+ content caused by an inhibition of SR Ca 2+ ATPase. The relationship curve between SpF and [Ca 2+ ] L (SpF -[Ca 2+ ] L ) during the addition of thapsigargin was markedly shifted to the left in KI cardiomyocytes compared to WT cardiomyocytes, thereby lowering the threshold of [Ca 2+ ] L to induce Ca 2+ sparks to approximately one-fifth in KI cardiomyocytes. In conclusion, the enhanced sensitivity of the RyR2 channel to activation by [Ca 2+ ] L : i.e. decreased threshold [Ca 2+ ] L to induce spontaneous Ca 2+ release, may be a primary cause of CPVT.

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.

Nebivolol suppresses cardiac ryanodine receptor-mediated spontaneous Ca2+ release and catecholaminergic polymorphic ventricular tachycardia

2016 ◽  
Vol 473 (22) ◽  
pp. 4159-4172 ◽  
Author(s):  
Zhen Tan ◽  
Zhichao Xiao ◽  
Jinhong Wei ◽  
Jingqun Zhang ◽  
Qiang Zhou ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Ryanodine Receptor ◽  
Critical Role ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Hek293 Cells ◽  
Polymorphic Ventricular Tachycardia ◽  
Triggered Arrhythmias ◽  
Β Blockers ◽  
Pleiotropic Properties ◽  
Cardiac Ryanodine Receptor

β-Blockers are a standard treatment for heart failure and cardiac arrhythmias. There are ∼30 commonly used β-blockers, representing a diverse class of drugs with different receptor affinities and pleiotropic properties. We reported that among 14 β-blockers tested previously, only carvedilol effectively suppressed cardiac ryanodine receptor (RyR2)-mediated spontaneous Ca2+ waves during store Ca2+ overload, also known as store overload-induced Ca2+ release (SOICR). Given the critical role of SOICR in arrhythmogenesis, it is of importance to determine whether there are other β-blockers that suppress SOICR. Here, we assessed the effect of other commonly used β-blockers on RyR2-mediated SOICR in HEK293 cells, using single-cell Ca2+ imaging. Of the 13 β-blockers tested, only nebivolol, a β-1-selective β-blocker with nitric oxide synthase (NOS)-stimulating action, effectively suppressed SOICR. The NOS inhibitor (N-nitro-l-arginine methyl ester) had no effect on nebivolol's SOICR inhibition, and the NOS activator (histamine or prostaglandin E2) alone did not inhibit SOICR. Hence, nebivolol's SOICR inhibition was independent of NOS stimulation. Like carvedilol, nebivolol reduced the opening of single RyR2 channels and suppressed spontaneous Ca2+ waves in intact hearts and catecholaminergic polymorphic ventricular tachycardia (CPVT) in the mice harboring a RyR2 mutation (R4496C). Interestingly, a non-β-blocking nebivolol enantiomer, (l)-nebivolol, also suppressed SOICR and CPVT without lowering heart rate. These data indicate that nebivolol, like carvedilol, possesses a RyR2-targeted action that suppresses SOICR and SOICR-evoked VTs. Thus, nebivolol represents a promising agent for Ca2+-triggered arrhythmias.

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