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Antagonists of L-type [Ca.sup.2+] channels (LTCCs) have been used to treat human cardiovascular diseases for decades. However, these inhibitors can have untoward effects in patients with heart failure, and their overall therapeutic profile remains nebulous given differential effects in the vasculature when compared with those in cardiomyocytes. To investigate this issue, we examined mice heterozygous for the gene encoding the pore-forming subunit of LTCC (calcium channel, voltage-dependent, L type, α1C subunit [Cacna1c mice; referred to herein as α1[C.sup.+/-] mice]) and mice in which this gene was loxP targeted to achieve graded heart-specific gene deletion (termed herein α1C-loxP mice). Adult cardiomyocytes from the hearts of α1[C.sup.-/+] mice at 10 weeks of age showed a decrease in LTCC current and a modest decrease in cardiac function, which we initially hypothesized would be cardioprotective. However, α1[C.sup.+/-] mice subjected to pressure overload stimulation, isoproterenol infusion, and swimming showed greater cardiac hypertrophy, greater reductions in ventricular performance, and greater ventricular dilation than α1[C.sup.+/-] controls. The same detrimental effects were observed in α1C-loxP animals with a cardiomyocytespecific deletion of one allele. More severe reductions in α1C protein levels with combinatorial deleted alleles produced spontaneous cardiac hypertrophy before 3 months of age, with early adulthood lethality. Mechanisti-cally, our data suggest that a reduction in LTCC current leads to neuroendocrine stress, with sensitized and leaky sarcoplasmic reticulum [Ca.sup.2+] release as a compensatory mechanism to preserve contractility. This state results in calcineurin/nuclear factor of activated T cells signaling that promotes hypertrophy and disease., Introduction Voltage-gated L-type [Ca.sup.2+] channels (LTCCs) are the primary source of [Ca.sup.2+] influx to initiate cardiac excitation-contraction coupling (ECC) (1, 2). The molecular composition of the LTCC in cardiomyocytes includes [...]

During the classic 'fight-or-flight' stress response, sympathetic nervous system activation leads to catechol-amine release, which increases heart rate and contractility, resulting in enhanced cardiac output. Catecholamines bind to β-adrenergic receptors, causing cAMP generation and activation of PKA, which phosphorylates multiple targets in cardiac muscle, including the cardiac ryanodine receptor/calcium release channel (RyR2) required for muscle contraction. PKA phosphorylation of RyR2 enhances channel activity by sensitizing the channel to cytosolic calcium ([Ca.sup.2+]). Here, we found that mice harboring RyR2 channels that cannot be PKA phosphorylated (referred to herein as RyR2-[S2808A.sup.+/+] mice) exhibited blunted heart rate and cardiac contractile responses to catecholamines (isoproterenol). The isoproterenol-induced enhancement of ventricular myocyte [Ca.sup.2+] transients and fractional shortening (contraction) and the spontaneous beating rate of sinoatrial nodal cells were all blunted in RyR2-[S2808A.sup.+/+] mice. The blunted cardiac response to catecholamines in RyR2-[S2808A.sup.+/+] mice resulted in impaired exercise capacity. RyR2-[S2808A.sup.+/+] mice were protected against chronic catecholaminergic-induced cardiac dysfunction. These studies identify what we believe to be new roles for PKA phosphorylation of RyR2 in both the heart rate and contractile responses to acute catecholaminergic stimulation., Introduction During exercise, heart rate (chronotropy) and cardiac contractility (inotropy) increase to meet the metabolic demands of the organs. Stress-induced activation of the sympathetic nervous system (SNS) results in catecholamine [...]

Increased sarcoplasmic reticulum (SR) [Ca.sup.2+] leak via the cardiac ryanodine receptor/calcium release channel (RyR2) is thought to play a role in heart failure (HF) progression. Inhibition of this leak is an emerging therapeutic strategy. To explore the role of chronic PKA phosphorylation of RyR2 in HF pathogenesis and treatment, we generated a knockin mouse with aspartic acid replacing serine 2808 (mice are referred to herein as RyR2-[S2808D.sup.+/+] mice). This mutation mimics constitutive PKA hyperphosphorylation of RyR2, which causes depletion of the stabilizing subunit FKBP12.6 (also known as calstabin2), resulting in leaky RyR2. RyR2-[S2808D.sup.+/+] mice developed age-dependent cardiomyopathy, elevated RyR2 oxidation and nitrosylation, reduced SR [Ca.sup.2+] store content, and increased diastolic SR [Ca.sup.2+] leak. After myocardial infarction, RyR2-[S2808D.sup.+/+] mice exhibited increased mortality compared with WT littermates. Treatment with S107, a 1,4-benzothiazepine derivative that stabilizes RyR2-calstabin2 interactions, inhibited the RyR2-mediated diastolic SR [Ca.sup.2+] leak and reduced HF progression in WT and RyR2-[S2808D.sup.+/+] mice. In contrast, β-adrenergic receptor blockers improved cardiac function in WT but not in RyR2-[S2808D.sup.+/+] mice.Thus, chronic PKA hyperphosphorylation of RyR2 results in a diastolic leak that causes cardiac dysfunction. Reversing PKA hyperphosphorylation of RyR2 is an important mechanism underlying the therapeutic action of β-blocker therapy in HF., Introduction Heart failure (HF), a syndrome characterized by progressive deterioration of cardiac function, represents a major public health burden and is a leading cause of morbidity and mortality in the [...]

The [Ca.sup.2+] release channel ryanodine receptor 2 (RyR2) is required for excitation-contraction coupling in the heart and is also present in the brain. Mutations in RyR2 have been linked to exercise-induced sudden cardiac death (catecholaminergic polymorphic ventricular tachycardia [CPVT]). CPVT-associated RyR2 mutations result in "leaky" RyR2 channels due to the decreased binding of the calstabin2 (FKBP12.6) subunit, which stabilizes the closed state of the channel. We found that mice heterozygous for the R2474S mutation in Ryr2 (Ryr2-R2474S mice) exhibited spontaneous generalized tonic-clonic seizures (which occurred in the absence of cardiac arrhythmias), exercise-induced ventricular arrhythmias, and sudden cardiac death. Treatment with a novel RyR2-specific compound (S107) that enhances the binding of calstabin2 to the mutant Ryr2-R2474S channel inhibited the channel leak and prevented cardiac arrhythmias and raised the seizure threshold. Thus, CPVT-associated mutant leaky Ryr2-R2474S channels in the brain can cause seizures in mice, independent of cardiac arrhythmias. Based on these data, we propose that CPVT is a combined neurocardiac disorder in which leaky RyR2 channels in the brain cause epilepsy, and the same leaky channels in the heart cause exercise-induced sudden cardiac death., Introduction Pharmacological seizure models have implicated abnormalities in intracellular [Ca.sup.2+] cycling of inhibitory interneurons and/or astrocytes as a mechanism of seizure generation (1), (2), and the inositol 1,4,5-trisphosphate receptor (IP3R), [...]

Abnormalities in intracellular calcium release and reuptake are responsible for decreased contractility in heart failure (HF). We have previously shown that cardiac ryanodine receptors (RyRs) are protein kinase A-hyperphosphorylated and depleted of the regulatory subunit calstabin-2 in HF. Moreover, similar alterations in skeletal muscle RyR have been linked to increased fatigability in HF. To determine whether restoration of calstabin binding to RyR may ameliorate cardiac and skeletal muscle dysfunction in HF, we treated WT and calstabin-[2.sup.-/-] mice subjected to myocardial infarction (MI) with JTV519. JTV519, a 1,4-benzothiazepine, is a member of a class of drugs known as calcium channel stabilizers, previously shown to increase calstabin binding to RyR. Echocardiography at 21 days after MI demonstrated a significant increase in ejection fraction in WT mice treated with JTV519 (45.8 [+ or -] 5.1%) compared with placebo (31.1 [+ or -] 3.1%; P < 0.05). Coimmunoprecipitation experiments revealed increased amounts of calstabin-2 bound to the RyR2 channel in JTV519-treated WT mice. However, JTV519 did not show any of these beneficial effects in calstabin-[2.sup.-/-] mice with MI. Additionally, JTV519 improved skeletal muscle fatigue in WT and calstabin-[2.sup.-/-] mice with HF by increasing the binding of calstabin-1 to RyR1. The observation that treatment with JTV519 improved cardiac function in WT but not calstabin-[2.sup.-/-] mice indicates that calstabin-2 binding to RyR2 is required for the beneficial effects in failing hearts. We conclude that JTV519 may provide a specific way to treat the cardiac and skeletal muscle myopathy in HF by increasing calstabin binding to RyR. calcium | FKBP12.6 | myocardial infarction | contractility

Ventricular arrhythmias can cause sudden cardiac death (SCD) in patients with normal hearts and in those with underlying disease such as heart failure. In animals with heart failure and in patients with inherited forms of exercise-induced SCD, depletion of the channel-stabilizing protein calstabin2 (FKBP12.6) from the ryanodine receptor-calcium release channel (RyR2) complex causes an intracellular [Ca.sup.2+] leak that can trigger fatal cardiac arrhythmias. A derivative of 1,4-benzothiazepine (JTV519) increased the affinity of calstabin2 for RyR2, which stabilized the closed state of RyR2 and prevented the [Ca.sup.2+] leak that triggers arrhythmias. Thus, enhancing the binding of calstabin2 to RyR2 may be a therapeutic strategy for common ventricular arrhythmias., Ventricular tachyarrhythmias that cause SCD are often associated with common heart diseases, such as heart failure, but may also occur in individuals without structural heart disease (1). Treatment remains largely [...]

Regulation by protein kinase A (PKA) of phosphorylation binding of FKBP12.6 to the calcium release channel (ryanodine receptor) is discussed relative to defective regulation in human hearts in decline. RyR2 is PKA hyperphosphorylated and that brings defective channel function caused by increased sensitivity to Ca(super.2+)-induced activation.

Sustained ryanodine receptor (RyR) Ca2+ leak is associated with pathological conditions such as heart failure or skeletal muscle weakness. We report that a single session of sprint interval training (SIT), but not of moderate intensity continuous training (MICT), triggers RyR1 protein oxidation and nitrosylation leading to calstabin1 dissociation in healthy human muscle and in in vitro SIT models (simulated SIT or S-SIT). This is accompanied by decreased sarcoplasmic reticulum Ca2+ content, increased levels of mitochondrial oxidative phosphorylation proteins, supercomplex formation and enhanced NADH-linked mitochondrial respiratory capacity. Mechanistically, (S-)SIT increases mitochondrial Ca2+ uptake in mouse myotubes and muscle fibres, and decreases pyruvate dehydrogenase phosphorylation in human muscle and mouse myotubes. Countering Ca2+ leak or preventing mitochondrial Ca2+ uptake blunts S-SIT-induced adaptations, a result supported by proteomic analyses. Here we show that triggering acute transient Ca2+ leak through RyR1 in healthy muscle may contribute to the multiple health promoting benefits of exercise. Ryanodine receptor type 1 (RyR1) are involved in skeletal muscle contraction. Here, the authors show that a transient calcium leak in response to exercise-induced post translational modifications of RyR1 causes mitochondrial remodeling to improve respiration. [ABSTRACT FROM AUTHOR]

Background: Advances in congestive heart failure (CHF) management depend on biomarkers for monitoring disease progression and therapeutic response. During systole, intracellular Ca2+ is released from the sarcoplasmic reticulum into the cytoplasm through type-2 ryanodine receptor/Ca2+ release channels. In CHF, chronically elevated circulating catecholamine levels cause pathological remodeling of type-2 ryanodine receptor/Ca2+ release channels resulting in diastolic sarcoplasmic reticulum Ca2+ leak and decreased myocardial contractility. Similarly, skeletal muscle contraction requires sarcoplasmic reticulum Ca2+ release through type-1 ryanodine receptors (RyR1), and chronically elevated catecholamine levels in CHF cause RyR1-mediated sarcoplasmic reticulum Ca2+ leak, contributing to myopathy and weakness. Circulating B-lymphocytes express RyR1 and catecholamine-responsive signaling cascades, making them a potential surrogate for defects in intracellular Ca2+ handling because of leaky RyR channels in CHF.Methods: Whole blood was collected from patients with CHF, CHF following left-ventricular assist device implant, and controls. Blood was also collected from mice with ischemic CHF, ischemic CHF+S107 (a drug that specifically reduces RyR channel Ca2+ leak), and wild-type controls. Channel macromolecular complex was assessed by immunostaining RyR1 immunoprecipitated from lymphocyte-enriched preparations. RyR1 Ca2+ leak was assessed using flow cytometry to measure Ca2+ fluorescence in B-lymphocytes in the absence and presence of RyR1 agonists that empty RyR1 Ca2+ stores within the endoplasmic reticulum.Results: Circulating B-lymphocytes from humans and mice with CHF exhibited remodeled RyR1 and decreased endoplasmic reticulum Ca2+ stores, consistent with chronic intracellular Ca2+ leak. This Ca2+ leak correlated with circulating catecholamine levels. The intracellular Ca2+ leak was significantly reduced in mice treated with the Rycal S107. Patients with CHF treated with left-ventricular assist devices exhibited a heterogeneous response.Conclusions: In CHF, B-lymphocytes exhibit remodeled leaky RyR1 channels and decreased endoplasmic reticulum Ca2+ stores consistent with chronic intracellular Ca2+ leak. RyR1-mediated Ca2+ leak in B-lymphocytes assessed using flow cytometry provides a surrogate measure of intracellular Ca2+ handling and systemic sympathetic burden, presenting a novel biomarker for monitoring response to pharmacological and mechanical CHF therapy. [ABSTRACT FROM AUTHOR]

Endothelial cells (ECs) are critical mediators of blood pressure (BP) regulation, primarily via the generation and release of vasorelaxants, including nitric oxide (NO). NO is produced in ECs by endothelial NO synthase (eNOS),which is activated by both calcium(Ca2+)-dependent and independent pathways. Here, we report that intracellular Ca2+ release from the endoplasmic reticulum(ER) via inositol 1,4,5-trisphosphate receptor (IP3R) is required for Ca2+-dependent eNOS activation. EC-specific type 1 1,4,5-trisphosphate receptor knockout (IP3R1-/-) mice are hypertensive and display blunted vasodilation in response to acetylcholine (ACh). Moreover, eNOS activity is reduced in both isolated IP3R1-deficient murine ECs and human ECs following IP3R1 knockdown. IP3R1 is upstream of calcineurin, a Ca2+/calmodulinactivated serine/threonine protein phosphatase. We show here that the calcineurin/nuclear factor of activated T cells (NFAT) pathway is less active and eNOS levels are decreased in IP3R1-deficient ECs. Furthermore, the calcineurin inhibitor cyclosporin A, whose use has been associated with the development of hypertension, reduces eNOS activity and vasodilation following ACh stimulation. Our results demonstrate that IP3R1 plays a crucial role in the ECmediated vasorelaxation and the maintenance of normal BP. [ABSTRACT FROM AUTHOR]