Shortened Ca2+ signaling refractoriness underlies cellular arrhythmogenesis in a postinfarction model of sudden cardiac death.

Rationale: Diastolic spontaneous Ca(2+) waves (DCWs) are recognized as important contributors to triggered arrhythmias. DCWs are thought to arise when [Ca(2+)] in sarcoplasmic reticulum ([Ca(2+)](SR)) reaches a certain threshold level, which might be reduced in cardiac disease as a consequence of sensitization of ryanodine receptors (RyR2s) to luminal Ca(2+).

Objective: We investigated the mechanisms of DCW generation in myocytes from normal and diseased hearts, using a canine model of post-myocardial infarction ventricular fibrillation (VF).

Regulation of myocyte contraction via neuronal nitric oxide synthase: role of ryanodine receptor S-nitrosylation.

The sarcoplasmic reticulum (SR) Ca(2+) release channel (ryanodine receptor, RyR2) has been proposed to be an end target of neuronal nitric oxide synthase (NOS1) signalling. The purpose of this study is to investigate the mechanism of NOS1 modulation of RyR2 activity and the corresponding effect on myocyte function. Myocytes were isolated from NOS1 knockout (NOS1(/)) and wild-type mice.

Redox modification of ryanodine receptors contributes to sarcoplasmic reticulum Ca2+ leak in chronic heart failure.

Abnormal cardiac ryanodine receptor (RyR2) function is recognized as an important factor in the pathogenesis of heart failure (HF). However, the specific molecular causes underlying RyR2 defects in HF remain poorly understood. In the present study, we used a canine model of chronic HF to test the hypothesis that the HF-related alterations in RyR2 function are caused by posttranslational modification by reactive oxygen species generated in the failing heart.

Protein protein interactions between triadin and calsequestrin are involved in modulation of sarcoplasmic reticulum calcium release in cardiac myocytes.

In cardiac muscle, intracellular Ca2+ release is controlled by a number of proteins including the ryanodine receptor (RyR2), calsequestrin (CASQ2), triadin-1 (Trd) and junctin (Jn) which form a complex in the junctional sarcoplasmic reticulum (SR) membrane. Within this complex, Trd appears to link CASQ2 to RyR2 although the functional significance of this interaction is unclear. In this study, we explored the functional importance of Trd-CASQ2 interactions for intracellular Ca2+ handling in rat ventricular myocytes.

Abnormal interactions of calsequestrin with the ryanodine receptor calcium release channel complex linked to exercise-induced sudden cardiac death.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a familial arrhythmogenic disorder associated with mutations in the cardiac ryanodine receptor (RyR2) and cardiac calsequestrin (CASQ2) genes. Previous in vitro studies suggested that RyR2 and CASQ2 interact as parts of a multimolecular Ca(2+)-signaling complex; however, direct evidence for such interactions and their potential significance to myocardial function remain to be determined. We identified a novel CASQ2 mutation in a young female with a structurally normal heart and unexplained syncopal episodes.

Abnormal intrastore calcium signaling in chronic heart failure.

Diminished Ca release from the sarcoplasmic reticulum (SR) is an important contributor to the impaired contractility of the failing heart. Despite extensive effort, the underlying causes of abnormal SR Ca release in heart failure (HF) remain unknown. We used a combination of simultaneous imaging of cytosolic and SR intraluminal [Ca] in isolated cardiomyocytes and recordings from single-ryanodine receptor (RyR) channels reconstituted into lipid bilayers to investigate alterations in intracellular Ca handling in an experimental model of chronic HF.

Triadin overexpression stimulates excitation-contraction coupling and increases predisposition to cellular arrhythmia in cardiac myocytes.

Triadin 1 (TRD) is an integral membrane protein that associates with the ryanodine receptor (RyR2), calsequestrin (CASQ2) and junctin to form a macromolecular Ca signaling complex in the cardiac junctional sarcoplasmic reticulum (SR). To define the functional role of TRD, we examined the effects of adenoviral-mediated overexpression of the wild-type protein (TRD(WT)) or a TRD mutant lacking the putative CASQ2 interaction domain residues 200 to 224 (TRD(Del.200-224)) on intracellular Ca signaling in adult rat ventricular myocytes.

Modulation of sarcoplasmic reticulum calcium release by calsequestrin in cardiac myocytes.

Calsequestrin (CASQ2) is a high capacity Ca-binding protein expressed inside the sarcoplasmic reticulum (SR). Mutations in the cardiac calsequestrin gene (CASQ2) have been linked to arrhythmias and sudden death induced by exercise and emotional stress. We have studied the function of CASQ2 and the consequences of arrhythmogenic CASQ2 mutations on intracellular Ca signalling using a combination of approaches of reverse genetics and cellular physiology in adult cardiac myocytes.

Modulation of cytosolic and intra-sarcoplasmic reticulum calcium waves by calsequestrin in rat cardiac myocytes.

Waves of Ca2+-induced Ca2+ release occur in various cell types and are involved in the pathology of certain forms of cardiac arrhythmia. These arrhythmias include catecholaminergic polymorphic ventricular tachycardia (CPVT), certain cases of which are associated with mutations in the cardiac calsequestrin gene (CASQ2). To explore the mechanisms of Ca2+ wave generation and unravel the underlying causes of CPVT, we investigated the effects of adenoviral-mediated changes in CASQ2 protein levels on the properties of cytosolic and sarcoplasmic reticulum (SR) Ca2+ waves in permeabilized rat ventricular myocytes.

The role of calsequestrin, triadin, and junctin in conferring cardiac ryanodine receptor responsiveness to luminal calcium.

The level of Ca inside the sarcoplasmic reticulum (SR) is an important determinant of functional activity of the Ca release channel/ryanodine receptor (RyR) in cardiac muscle. However, the molecular basis of RyR regulation by luminal Ca remains largely unknown. In the present study, we investigated the potential role of the cardiac SR luminal auxiliary proteins calsequestrin (CSQ), triadin 1, and junctin in forming the luminal calcium sensor for the cardiac RyR.

Abnormal calcium signaling and sudden cardiac death associated with mutation of calsequestrin.

Mutations in human cardiac calsequestrin (CASQ2), a high-capacity calcium-binding protein located in the sarcoplasmic reticulum (SR), have recently been linked to effort-induced ventricular arrhythmia and sudden death (catecholaminergic polymorphic ventricular tachycardia). However, the precise mechanisms through which these mutations affect SR function and lead to arrhythmia are presently unknown. In this study, we explored the effect of adenoviral-directed expression of a canine CASQ2 protein carrying the catecholaminergic polymorphic ventricular tachycardia-linked mutation D307H (CASQ2(D307H)) on Ca2+ signaling in adult rat myocytes.

Calsequestrin determines the functional size and stability of cardiac intracellular calcium stores: Mechanism for hereditary arrhythmia.

Calsequestrin is a high-capacity Ca-binding protein expressed inside the sarcoplasmic reticulum (SR), an intracellular Ca release and storage organelle in muscle. Mutations in the cardiac calsequestrin gene (CSQ2) have been linked to arrhythmias and sudden death. We have used Ca-imaging and patch-clamp methods in combination with adenoviral gene transfer strategies to explore the function of CSQ2 in adult rat heart cells.

Protein phosphatases decrease sarcoplasmic reticulum calcium content by stimulating calcium release in cardiac myocytes.

Phosphorylation/dephosphorylation of Ca2+ transport proteins by cellular kinases and phosphatases plays an important role in regulation of cardiac excitation-contraction coupling; furthermore abnormal protein kinase and phosphatase activities have been implicated in heart failure. However, the precise mechanisms of action of these enzymes on intracellular Ca2+ handling in normal and diseased hearts remains poorly understood. We have investigated the effects of protein phosphatases PP1 and PP2A on spontaneous Ca2+ sparks and SR Ca2+ load in myocytes permeabilized with saponin.

Regulation of sarcoplasmic reticulum calcium release by luminal calcium in cardiac muscle.

The amount of Ca2+ released from the sarcoplasmic reticulum (SR) is a principal determinant of cardiac contractility. Normally, the SR Ca2+ stores are mobilized through the mechanism of Ca2+-induced Ca2+ release (CICR). In this process, Ca2+ enters the cell through plasmalemmal voltage-dependent Ca2+ channels to activate the Ca2+ release channels in the SR membrane.