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During exercise or stress, the sympathetic system stimulates cardiac contractility via β‐adrenergic receptor (β‐AR) activation, resulting in phosphorylation of the cardiac ryanodine receptor (RyR2). Three RyR2 phosphorylation sites have taken prominence in excitation–contraction coupling: S2808 and S2030 are described as protein kinase A specific and S2814 as a Ca2+/calmodulin kinase type‐2‐specific site. To examine the contribution of these phosphosites to Ca2+ signalling, we generated double knock‐in (DKI) mice in which Ser2808 and Ser2814 phosphorylation sites have both been replaced by alanine (RyR2‐S2808A/S2814A). These mice did not exhibit an overt phenotype. Heart morphology and haemodynamic parameters were not altered. However, they had a higher susceptibility to arrhythmias. We performed confocal Ca2+ imaging and electrophysiology experiments. Isoprenaline was used to stimulate β‐ARs. Measurements of Ca2+ waves and latencies in myocytes revealed an increased propensity for spontaneous Ca2+ releases in DKI myocytes, both in control conditions and during β‐AR stimulation. In DKI cells, waves were initiated from a lower threshold concentration of Ca2+ inside the sarcoplasmic reticulum, suggesting higher Ca2+ sensitivity of the RyRs. The refractoriness of Ca2+ spark triggering depends on the Ca2+ sensitivity of the RyR2. We found that RyR2‐S2808A/S2814A channels were more Ca2+ sensitive in control conditions. Isoprenaline further shortened RyR refractoriness in DKI cardiomyocytes. Together, our results suggest that ablation of both the RyR2‐Ser2808 and RyR2‐S2814 sites increases the propensity for pro‐arrhythmic spontaneous Ca2+ releases, as previously suggested for hyperphosphorylated RyRs. Given that the DKI cells present a full response to isoprenaline, the data suggest that phosphorylation of Ser2030 might be sufficient for β‐AR‐mediated sensitization of RyRs. Key points: Phosphorylation of cardiac sarcoplasmic reticulum Ca2+‐release channels (ryanodine receptors, RyRs) is involved in the regulation of cardiac function.Ablation of both the RyR2‐Ser2808 and RyR2‐Ser2814 sites increases the propensity for pro‐arrhythmic spontaneous Ca2+ releases, as previously suggested for hyperphosphorylated RyRs.The intra‐sarcoplasmic reticulum Ca2+ threshold for spontaneous Ca2+ wave generation is lower in RyR2‐double‐knock‐in cells.The RyR2 from double‐knock‐in cells exhibits increased Ca2+ sensitivity.Phosphorylation of Ser2808 and Ser2814 might be important for basal activity of the channel.Phosphorylation of Ser2030 might be sufficient for a β‐adrenergic response. [ABSTRACT FROM AUTHOR]

Striated muscle cells, encompassing cardiac myocytes and skeletal muscle fibers, are fundamental to athletic performance, facilitating blood circulation and coordinated movement through contraction. Despite their distinct functional roles, these muscle types exhibit similarities in cytoarchitecture, protein expression, and excitation-contraction coupling. Both muscle types also undergo molecular remodeling in energy metabolism and cell size in response to acute and repeated exercise stimuli to enhance exercise performance. Reactive oxygen species (ROS) produced by NADPH oxidase (NOX) isoforms 2 and 4 have emerged as signaling molecules that regulate exercise adaptations. This review systematically compares NOX2 and NOX4 expression, regulation, and roles in cardiac and skeletal muscle responses across exercise modalities. We highlight the many gaps in our knowledge and opportunities to let future skeletal muscle research into NOX-dependent mechanisms be inspired by cardiac muscle studies and vice versa. Understanding these processes could enhance the development of exercise routines to optimize human performance and health strategies that capitalize on the advantages of physical activity. [Display omitted] • Striated muscle cells exhibit many redox-regulated similarities, including the expression of NOX2 and NOX4. • NOX2 and NOX4 are linked to responses to exercise in skeletal and cardiac muscles, influencing glucose metabolism and cell growth. • Further studies on NOX-dependent redox regulation of striated skeletal muscle may improve our understanding of the factors that limit human performance. [ABSTRACT FROM AUTHOR]

Omecamtiv mecarbil (OM) is a small molecule that has been shown to improve the function of the slow human ventricular myosin (MyHC) motor through a complex perturbation of the thin/thick filament regulatory state of the sarcomere mediated by binding to myosin allosteric sites coupled to inorganic phosphate (Pi) release. Here, myofibrils from samples of human left ventricle (β-slow MyHC-7) and left atrium (α-fast MyHC-6) from healthy donors were used to study the differential effects of μmolar [OM] on isometric force in relaxing conditions (pCa 9.0) and at maximal (pCa 4.5) or half-maximal (pCa 5.75) calcium activation, both under control conditions (15 °C; equimolar DMSO; contaminant inorganic phosphate [Pi] ~170 μM) and in the presence of 5 mM [Pi]. The activation state and OM concentration within the contractile lattice were rapidly altered by fast solution switching, demonstrating that the effect of OM was rapid and fully reversible with dose-dependent and myosin isoform-dependent features. In MyHC-7 ventricular myofibrils, OM increased submaximal and maximal Ca2+-activated isometric force with a complex dose-dependent effect peaking (40% increase) at 0.5 μM, whereas in MyHC-6 atrial myofibrils, it had no effect or—at concentrations above 5 µM—decreased the maximum Ca2+-activated force. In both ventricular and atrial myofibrils, OM strongly depressed the kinetics of force development and relaxation up to 90% at 10 μM [OM] and reduced the inhibition of force by inorganic phosphate. Interestingly, in the ventricle, but not in the atrium, OM induced a large dose-dependent Ca2+-independent force development and an increase in basal ATPase that were abolished by the presence of millimolar inorganic phosphate, consistent with the hypothesis that the widely reported Ca2+-sensitising effect of OM may be coupled to a change in the state of the thick filaments that resembles the on–off regulation of thin filaments by Ca2+. The complexity of this scenario may help to understand the disappointing results of clinical trials testing OM as inotropic support in systolic heart failure compared with currently available inotropic drugs that alter the calcium signalling cascade. [ABSTRACT FROM AUTHOR]

Myotropes are pharmaceuticals that have recently been developed or are under investigation for the treatment of heart diseases. Myotropes have had varied success in clinical trials. Initial research into myotropes have widely focused on animal models of cardiac dysfunction in comparison with normal animal cardiac physiology—primarily using males. In this study we examined the effect of danicamtiv, which is one type of myotrope within the class of myosin activators, on contractile function in permeabilized (skinned) myocardial strips from male and female Sprague–Dawley rats. We found that danicamtiv increased steady-state isometric force production at sub-maximal calcium levels, leading to greater Ca2+-sensitivity of contraction for both sexes. Danicamtiv did not affect maximal Ca2+-activated force for either sex. Sinusoidal length-perturbation analysis was used to assess viscoelastic myocardial stiffness and cross-bridge cycling kinetics. Data from these measurements did not vary with sex, and the data suggest that danicamtiv slows cross-bridge cycling kinetics. These findings imply that danicamtiv increases force production via increasing cross-bridge contributions to activation of contraction, especially at sub-maximal Ca2+-activation. The inclusion of both sexes in animal models during the formative stages of drug development could be helpful for understanding the efficacy or limitation of a drug's therapeutic impact on cardiac function. [ABSTRACT FROM AUTHOR]

AbstractDoxorubicin (Dox) is an effective and commonly used anticancer drug; however, it leads to several side effects including cardiotoxicity which contributes to poor quality of life for cancer patients. Creatine (Cr) is a promising intervention to alleviate Dox-induced cardiotoxicity. This study aimed to examine the effects of Cr beforeDox on cardiac mitochondrial creatine kinase (MtCK). Male rats were randomly assigned to one of two 4-week Cr feeding interventions (standard Cr diet or Cr loading diet) or a control diet (Con, n = 20). Rats in the standard Cr diet (Cr1, n = 20) were fed 2% Cr for 4-weeks. Rats in the Cr loading diet (Cr2, n = 20) were fed 4% Cr for 1-week followed by 2% Cr for 3-weeks. After 4-weeks, rats received either a bolus injection of 15 mg/kg Dox or a placebo saline injection (Sal). Five days post-injections left ventricle (LV) was excised and analyzed for MtCK expression using Western blot and ELISA. A significant drug effect was observed for LV mass (p < 0.05), post hoc testing revealed LV mass of Con + Dox and Cr2 + Dox was significantly lower than Con + Sal (p < 0.05). A significant drug effect was observed for MtCK (p = 0.03) through Western blot. A significant drug effect (p = 0.03) and interaction (p = 0.02) was observed for MtCK using ELISA. Post hoc testing revealed that Cr2 + Dox had significantly higher MtCK than Cr1 + Sal and Cr2 + Sal. Data suggest that a reduction in LV mass and MtCK may contribute to Dox-induced cardiotoxicity, and Cr supplementation may play a potential role in mitigating cardiotoxicity by preserving mitochondrial CK. [ABSTRACT FROM AUTHOR]

This article explores the movement of sarcomeres in the heart muscle and the role of the protein titin in this process. It challenges previous beliefs by showing that sarcomeres do not all move in synchrony during muscle contraction. The asynchrony is influenced by factors such as sarcomere length and calcium levels. The article suggests that this asynchrony may contribute to impaired heart function in conditions like dilated cardiomyopathy. Further research is needed to understand the link between sarcomere movement and heart disease. [Extracted from the article]

Lead and cadmium are heavy metals widely distributed in the environment and contribute significantly to cardiovascular morbidity and mortality. Using Leadmium Green dye, we have shown that lead and cadmium enter cardiomyocytes, distributing throughout the cell. Using an in vitro motility assay, we have shown that sliding velocity of actin and native thin filaments over myosin decreases with increasing concentrations of Pb2+ and Cd2+. Significantly lower concentrations of Pb2+ and Cd2+ (0.6 mM) were required to stop sliding of thin filaments over myosin compared to the stopping actin sliding over the same myosin (1.1-1.6 mM). Lower concentration of Cd2+ (1.1 mM) needed to stop actin sliding over myosin compared to the Pb2++Cd2+ combination (1.3 mM) and lead alone (1.6 mM). There were no differences found in the effects of lead and cadmium cations on relative force developed by myosin heads or number of actin filaments bound to myosin. Sliding velocity of actin over myosin in the left atrium, right and left ventricles changed equally when exposed to the same dose of the same metal. Thus, we have demonstrated for the first time that Pb2+ and Cd2+ can directly affect myosin and thin filament function, with Cd2+ exerting a more toxic influence on myosin function compared to Pb2+. [ABSTRACT FROM AUTHOR]

The impact of tissue engineering has extended beyond a traditional focus in medicine to the rapidly growing realm of biohybrid robotics. Leveraging living actuators as functional components in machines has been a central focus of this field, generating a range of compelling demonstrations of robots capable of muscle-powered swimming, walking, pumping, gripping, and even computation. In this review, we highlight key advances in fabricating tissue-scale cardiac and skeletal muscle actuators for a range of functional applications. We discuss areas for future growth including scalable manufacturing, integrated feedback control, and predictive modeling and also propose methods for ensuring inclusive and bioethics-focused pedagogy in this emerging discipline. We hope this review motivates the next generation of biomedical engineers to advance rational design and practical use of living machines for applications ranging from telesurgery to manufacturing to on- and off-world exploration. [ABSTRACT FROM AUTHOR]

Maintaining the structure of cardiac membranes and membrane organelles is essential for heart function. A critical cardiac membrane organelle is the transverse tubule system (called the t-tubule system) which is an invagination of the surface membrane. A unique structural characteristic of the cardiac muscle t-tubule system is the extension of the extracellular matrix (ECM) from the surface membrane into the t-tubule lumen. However, the importance of the ECM extending into the cardiac t-tubule lumen is not well understood. Dystroglycan (DG) is an ECM receptor in the surface membrane of many cells, and it is also expressed in t-tubules in cardiac muscle. Extensive posttranslational processing and O-glycosylation are required for DG to bind ECM proteins and the binding is mediated by a glycan structure known as matriglycan. Genetic disruption resulting in defective O-glycosylation of DG results in muscular dystrophy with cardiorespiratory pathophysiology. Here, we show that DG is essential for maintaining cardiac t-tubule structural integrity. Mice with defects in O-glycosylation of DG developed normal t-tubules but were susceptible to stress-induced t-tubule loss or severing that contributed to cardiac dysfunction and disease progression. Finally, we observed similar stress-induced cardiac t-tubule disruption in a cohort of mice that solely lacked matriglycan. Collectively, our data indicate that DG in t-tubules anchors the luminal ECM to the t-tubule membrane via the polysaccharide matriglycan, which is critical to transmitting structural strength of the ECM to the t-tubules and provides resistance to mechanical stress, ultimately preventing disruptions in cardiac t-tubule integrity. [ABSTRACT FROM AUTHOR]

Mechanisms of interaction of ionizing radiation with biological objects are a chain of successive physical and physico-chemical changes, which manifest themselves in the form of excitation, primary and secondary ionization of molecules. Biosynthesis of ATP, which is carried out by a system of oxidation-reduction enzymes localized in the inner membrane of mitochondria - the respiratory chain, belongs to the vital processes that are directly disturbed under the action of ionizing radiation. The high degree of damage to this system is due to the significant radiosensitivity of metal-containing enzymes. The purpose of the work is to study the formation of the adaptive response of muscle tissue of sexually mature rats to the influence of ionizing radiation at a dose of 0.5 Gy. It was concluded that a day after irradiation with the dose of 0.5 Gy, the content of contractile proteins in skeletal muscle decreases slightly. On the 15th day, the content of contractile proteins began to decrease. By the 30th day, the content of contractile proteins decreased by 22.9% for myosin, by more than 11% for actin, and by 7 and 8% for troponin and tropomyosin, respectively, compared to the values of the intact group. A similar picture is observed in the cardiac muscle. Mg2+,Ca2+-ATP-ase activity of actomyosin, starting from the 1st day was shown to be increased in both the skeletal and cardiac muscles, reaching its peak in the cardiac muscle on the 15th day, in contrast to the skeletal muscle, where this indicator reached its peak on the 7th day. The authors conclude that irradiation of sexually mature animals with the dose of 0.5 Gy forms an adaptive response that is accompanied by an increase in Mg2+,Ca2+-ATP-ase activity due to the formation of a strong form of binding between F-actin and myosin, actin monomers go into the typical for actomyosin “turned on stage”, and the myosin heads acquire an ordered orientation in the muscle fiber. According to author’s idea, the data obtained indicated the benefit and reasonability of using in post-radiation dysfunctions complex pharmacological treatment drugs that are able to normalize intracellular homeostasis, eliminate probable acidic changes initiated by radiation exposure, activate the processes of intramuscle energy generation and which have protective properties in relation to the muscular system.

Membrane contact sites between endoplasmic reticulum (ER) and plasma membrane (PM), or ER-PM junctions, are found in all eukaryotic cells. In excitable cells they play unique roles in organizing diverse forms of Ca2+ signaling as triggered by membrane depolarization. ER-PM junctions underlie crucial physiological processes such as excitation-contraction coupling, smooth muscle contraction and relaxation, and various forms of activity-dependent signaling and plasticity in neurons. In many cases the structure and molecular composition of ER-PM junctions in excitable cells comprise important regulatory feedback loops linking depolarization-induced Ca2+ signaling at these sites to the regulation of membrane potential. Here, we describe recent findings on physiological roles and molecular composition of native ER-PM junctions in excitable cells. We focus on recent studies that provide new insights into canonical forms of depolarization-induced Ca2+ signaling occurring at junctional triads and dyads of striated muscle, as well as the diversity of ER-PM junctions in these cells and in smooth muscle and neurons.

Abstract In a previous report, we demonstrated that Cbx1, PurB and Sp3 inhibited cardiac muscle differentiation by increasing nucleosome density around cardiac muscle gene promoters. Since cardiac and skeletal muscle express many of the same proteins, we asked if Cbx1, PurB and Sp3 similarly regulated skeletal muscle differentiation. In a C2C12 model of skeletal muscle differentiation, Cbx1 and PurB knockdown increased myotube formation. In contrast, Sp3 knockdown inhibited myotube formation, suggesting that Sp3 played opposing roles in cardiac muscle and skeletal muscle differentiation. Consistent with this finding, Sp3 knockdown also inhibited various muscle-specific genes. The Cbx1, PurB and Sp3 proteins are believed to influence gene-expression in part by altering nucleosome position. Importantly, we developed a statistical approach to determine if changes in nucleosome positioning were significant and applied it to understanding the architecture of muscle-specific genes. Through this novel statistical approach, we found that during myogenic differentiation, skeletal muscle-specific genes undergo a set of unique nucleosome changes which differ significantly from those shown in commonly expressed muscle genes. While Sp3 binding was associated with nucleosome loss, there appeared no correlation with the aforementioned nucleosome changes. In summary, we have identified a novel role for Sp3 in skeletal muscle differentiation and through the application of quantifiable MNase-seq have discovered unique fingerprints of nucleosome changes for various classes of muscle genes during myogenic differentiation.

In a previous report, we demonstrated that Cbx1, PurB and Sp3 inhibited cardiac muscle differentiation by increasing nucleosome density around cardiac muscle gene promoters. Since cardiac and skeletal muscle express many of the same proteins, we asked if Cbx1, PurB and Sp3 similarly regulated skeletal muscle differentiation. In a C2C12 model of skeletal muscle differentiation, Cbx1 and PurB knockdown increased myotube formation. In contrast, Sp3 knockdown inhibited myotube formation, suggesting that Sp3 played opposing roles in cardiac muscle and skeletal muscle differentiation. Consistent with this finding, Sp3 knockdown also inhibited various muscle-specific genes. The Cbx1, PurB and Sp3 proteins are believed to influence gene-expression in part by altering nucleosome position. Importantly, we developed a statistical approach to determine if changes in nucleosome positioning were significant and applied it to understanding the architecture of muscle-specific genes. Through this novel statistical approach, we found that during myogenic differentiation, skeletal muscle-specific genes undergo a set of unique nucleosome changes which differ significantly from those shown in commonly expressed muscle genes. While Sp3 binding was associated with nucleosome loss, there appeared no correlation with the aforementioned nucleosome changes. In summary, we have identified a novel role for Sp3 in skeletal muscle differentiation and through the application of quantifiable MNase-seq have discovered unique fingerprints of nucleosome changes for various classes of muscle genes during myogenic differentiation. [ABSTRACT FROM AUTHOR]

Concerted robust opening of cardiac ryanodine receptors' (RyR2) Ca2+ release 1oplasmic reticulum (SR) is fundamental for normal systolic cardiac function. During diastole, infrequent spontaneous RyR2 openings mediate the SR Ca2+ leak that normally constrains SR Ca2+ load. Abnormal large diastolic RyR2-mediated Ca2+ leak events can cause delayed after depolarizations (DADs) and arrhythmias. The RyR2-associated mechanisms underlying these processes are being extensively studied at multiple levels utilizing various model animals. Since there are well-described species-specific differences in cardiac intracellular Ca2+ handing in situ, we tested whether or not single RyR2 function in vitro retains this species specificity. We isolated RyR2-rich heavy SR microsomes from mouse, rat, rabbit, and human ventricular muscle and quantified RyR2 function using identical solutions and methods. The single RyR2 cytosolic Ca2+ sensitivity was similar across these species. However, there were significant species differences in single RyR2 mean open times in both systole and diastole-like solutions. In diastole-like solutions, single rat/mouse RyR2 open probability and frequency of long openings (> 6 ms) were similar, but these values were significantly greater than those of either single rabbit or human RyR2s. We propose these in vitro single RyR2 functional differences across species stem from the species-specific RyR2 regulatory environment present in the source tissue. Our results show the single rabbit RyR2 functional attributes, particularly in diastole-like conditions, replicate those of single human RyR2 best among the species tested. [ABSTRACT FROM AUTHOR]

The review provides a brief analysis of the current knowledge of such a post-translational modification of titin as phosphorylation, with a focus on changes that occur during the development of heart diseases. Studies using animal models of heart diseases and cardiac biopsy from patients with various pathologies reveal changes in the level of titin phosphorylation compared to healthy controls. The development of cardiac pathology is typically accompanied by hyperphosphorylation of the S11878 site and hypophosphorylation of the S12022 site in the titin PEVK region, as well as changes in the level of site phosphorylation in the titin N2B region. The cooperative functional effect of these changes is an increase in the stiffness of cardiomyocytes and cardiac muscle as a whole, based on the viscoelastic properties of titin. Changes in the latter, in turn, result from hypo- or hyperphosphorylation of certain titin sites. The review also addresses a number of therapeutic approaches aimed at modifying titin phosphorylation levels as a means to manage viscoelastic properties of the pathological myocardium in order to normalize its contractility. [ABSTRACT FROM AUTHOR]

The different embryological origins of striated muscle tissue make it an interesting tissue but at the same time difficult to understand, this is how the musculature of the face comes from the first pharyngeal arch, on the other hand. The muscles of the tongue derive from the somites. The muscles of the larynx come from the pharyngeal arches. The muscles of the spine come from the medial or internal myotome of the somite, while the muscles of the limbs and body wall come from the external myotome. The cardiac musculature originates from the lateral splanchnic mesoderm. In this work, the development of myoblasts in human, mouse and chicken fetuses was studied in the facial region, tongue, and spine, limbs, body wall and cardiac muscles using histological histochemical techniques and immunohistochemical technique. The objective of the work is to compare the histogenesis of striated muscle (skeletal, visceral and cardiac), indicating the differences in origin, evolution of the morphological characteristics in each of them and the signaling routes that are involved in its development. [ABSTRACT FROM AUTHOR]

Force generation in striated muscle is primarily controlled by structural changes in the actin-containing thin filaments triggered by an increase in intracellular calcium concentration. However, recent studies have elucidated a new class of regulatory mechanisms, based on the myosin-containing thick filament, that control the strength and speed of contraction by modulating the availability of myosin motors for the interaction with actin. This review summarizes the mechanisms of thin and thick filament activation that regulate the contractility of skeletal and cardiac muscle. A novel dual-filament paradigm of muscle regulation is emerging, in which the dynamics of force generation depends on the coordinated activation of thin and thick filaments. We highlight the interfilament signaling pathways based on titin and myosin-binding protein-C that couple thin and thick filament regulatory mechanisms. This dual-filament regulation mediates the length-dependent activation of cardiac muscle that underlies the control of the cardiac output in each heartbeat. [ABSTRACT FROM AUTHOR]

A progressive neurological disorder was observed in a male neutered Weimaraner. Clinical signs included fecal incontinence, lethargy, moderate paraparesis, proprioceptive pelvic limb ataxia, falling, cognitive decline, incoordination, decreased interest in food, changes in posture, and episodes of trance-like behavior. Neurologic signs were first observed at approximately 4 years, 10 months of age and progressed slowly. Magnetic resonance imaging showed generalized brain atrophy with areas of white matter pathology. Humane euthanasia was elected at 6 years, 7 months of age due to increasing severity of the neurological signs. Autofluorescent intracellular granules were observed in the cerebral and cerebellar cortexes, optic nerve, and cardiac muscle of the affected dog. These abnormal inclusions in the cerebral cortex and cardiac muscle immunolabeled with antibodies to mitochondrial ATP synthase subunit c protein, like that observed in the neuronal ceroid lipofuscinosis group of lysosomal storage diseases. Immunolabeling also demonstrated pronounced neuroinflammation in brain tissues. The ultrastructural appearances of the disease-related inclusion bodies in the brain and optic nerve were quite variable. The ultrastructure and locations of many of the inclusions in the nervous tissues suggested that they were derived, at least in part, from the myelin surrounding axons. The storage bodies in the cardiac muscle were located in mitochondria-rich regions and consisted of parallel arrays of membrane-like components interspersed with electron-dense flocculent material. The disease was characterized by pronounced abnormalities in the myelin of the brain and optic nerve consisting of distinctive areas of ballooning between the layers of myelin. The whole genome sequence generated from the affected dog contained a homozygous G-to-A missense mutation in CNP, which encodes proteins with CNPase enzyme activity and a structural role in myelin. The mutation predicts a Thr42Met amino acid sequence substitution. Genotyping of archived Weimaraner DNA samples identified an additional G > A variant homozygote with a clinical history and brain lesions similar to those of the proband. Of 304 Weimaraners and over 4000 other dogs of various breeds, the proband and the other Weimaraner that exhibited similar signs were the only two that were homozygous for the CNP missense variant. CNPase immunolabeling was widespread in brain tissues from normal dogs but was undetectable in the same tissues from the proband. Based on the clinical history, fluorescence and electron-microscopy, immunohistochemistry, and molecular genetic findings, the late-onset Weimaraner disorder likely results from the missense mutation that results in CNPase deficiency, leading to myelin abnormalities, accumulation of lysosomal storage bodies, and brain atrophy. Similar disorders have been associated with different CNP variants in Dalmatians and in human subjects. [ABSTRACT FROM AUTHOR]

Omecamtiv mecarbil (OM) is a small molecule that has been shown to improve the function of the slow human ventricular myosin (MyHC) motor through a complex perturbation of the thin/thick filament regulatory state of the sarcomere mediated by binding to myosin allosteric sites coupled to inorganic phosphate (Pi) release. Here, myofibrils from samples of human left ventricle (β-slow MyHC-7) and left atrium (α-fast MyHC-6) from healthy donors were used to study the differential effects of μmolar [OM] on isometric force in relaxing conditions (pCa 9.0) and at maximal (pCa 4.5) or half-maximal (pCa 5.75) calcium activation, both under control conditions (15 °C; equimolar DMSO; contaminant inorganic phosphate [Pi] ~170 μM) and in the presence of 5 mM [Pi]. The activation state and OM concentration within the contractile lattice were rapidly altered by fast solution switching, demonstrating that the effect of OM was rapid and fully reversible with dose-dependent and myosin isoform-dependent features. In MyHC-7 ventricular myofibrils, OM increased submaximal and maximal Ca2+-activated isometric force with a complex dose-dependent effect peaking (40% increase) at 0.5 μM, whereas in MyHC-6 atrial myofibrils, it had no effect or—at concentrations above 5 µM—decreased the maximum Ca2+-activated force. In both ventricular and atrial myofibrils, OM strongly depressed the kinetics of force development and relaxation up to 90% at 10 μM [OM] and reduced the inhibition of force by inorganic phosphate. Interestingly, in the ventricle, but not in the atrium, OM induced a large dose-dependent Ca2+-independent force development and an increase in basal ATPase that were abolished by the presence of millimolar inorganic phosphate, consistent with the hypothesis that the widely reported Ca2+-sensitising effect of OM may be coupled to a change in the state of the thick filaments that resembles the on–off regulation of thin filaments by Ca2+. The complexity of this scenario may help to understand the disappointing results of clinical trials testing OM as inotropic support in systolic heart failure compared with currently available inotropic drugs that alter the calcium signalling cascade.

Cardiac myosin binding protein C (cMyBP-C) is one of the essential control components of the myosin cross-bridge cycle. The C-terminal part of cMyBP-C is located on the surface of the thick filament, and its N-terminal part interacts with actin, myosin, and tropomyosin, affecting both kinetics of the ATP hydrolysis cycle and lifetime of the cross-bridge, as well as calcium regulation of the actin–myosin interaction, thereby modulating contractile function of myocardium. The role of cMyBP-C in atrial contraction has not been practically studied. We examined effect of the N-terminal C0-C1-m-C2 (C0-C2) fragment of cMyBP-C on actin–myosin interaction using ventricular and atrial myosin in an in vitro motility assay. The C0-C2 fragment of cMyBP-C significantly reduced the maximum sliding velocity of thin filaments on both myosin isoforms and increased the calcium sensitivity of the actin–myosin interaction. The C0-C2 fragment had different effects on the kinetics of ATP and ADP exchange, increasing the affinity of ventricular myosin for ADP and decreasing the affinity of atrial myosin. The effect of the C0-C2 fragment on the activation of the thin filament depended on the myosin isoforms. Atrial myosin activates the thin filament less than ventricular myosin, and the C0-C2 fragment makes these differences in the myosin isoforms more pronounced. [ABSTRACT FROM AUTHOR]

Seasonally breeding birds express variations of traits (phenotypic flexibility) throughout their life history stages that represent adaptations to environmental conditions. Changes of body condition during migration have been well studied, whereas alterations of skeletal and cardiac muscles, body mass, and fat scores have yet to be characterized throughout the spring or fall migratory stages. Additionally, we examined flexible patterns of muscle, body mass, and fat score in migrant white-crowned sparrows (Zonotrichia leucophrys gambelii) in comparison with those in a resident subspecies (Zonotrichia leucophrys nuttalli) during the stages they share to evaluate the influence of different life histories. Migrants showed hypertrophy of the pectoralis muscle fiber area on the wintering grounds in late prealternate molt, yet increased pectoralis muscle mass was not detected until birds readied for spring departure. While pectoralis profile and fat scores enlarged at predeparture in spring and fall, pectoralis, cardiac, and body masses were greater only in spring stages, suggesting seasonal differences for migratory preparation. Gastrocnemius mass showed little change throughout all stages, whereas gastrocnemius fiber area declined steadily but rebounded in fall on the wintering grounds, where migrants become more sedentary. In general, residents are heavier birds with larger leg structures, while migrants sport longer wings and greater heart mass. Phenotypic flexibility was most prominent among residents with peaks of pectoralis, gastrocnemius, and body masses during the winter stage, when local weather is most severe. Thus, the subspecies express specific patterns of phenotypic flexibility with peaks coinciding with the stages of heightened energy demands: the winter stage for residents and the spring stages for migrants. [ABSTRACT FROM AUTHOR]

Introduction: Nandrolone (ND) is one of the Anabolic-androgenic steroid widely used among athletes in doses that result in severe adverse effects on many organs specially heart. Nigella sativa oil and Omega-3 have antioxidant effect. Aim of the Work: To evaluate the potential defensive effect of Nigella sativa oil and Omega-3 on Nandrolone-induced cardiac muscle histological changes in rats. Materials and Methods: Forty adult male rats, were divided into four groups, Group I (control group). Group II; treated with ND only (10 mg/kg b.w.) 3 times per week injection for 6 weeks. Group III; treated with ND as group II and N. sativa oil orally (400 mg/kg b.w.) daily for 6 weeks. Group IV; treated with ND as group II and omega- 3 orally (400 mg/kg b.w.) daily for 6 weeks. Then cardiac muscle specimens prepared for histological and immunohistochemical studies by light and electron microscopes. Results: Group II showed marked distortion, fragmentation, loss of cardiac muscle striation, inflammatory cellular infiltrations, significantly increased deposition of collagen fibers, interruption in intercalated disc. Significantly increased immuno- expressions of Caspase-3 and alpha –Smooth muscle actin (α-SMA) when compared to control group. Group III & IV that treated with either Nigella sativa oil or Omega-3 respectively showed improvement of the histological architecture of cardiac muscle and significantly decreased immune- expressions of Caspase-3 and alpha –Smooth muscle actin (α-SMA) when compared to group II. Conclusion: Nigella sativa oil and Omega-3 could protect the heart from the injurious effect of ND. The results of Nigella sativa oil were better than Omega-3 at histological and immunohistochemical levels. [ABSTRACT FROM AUTHOR]

The effect of mechano‐electrical feedback on re‐entry formation and maintenance was studied using a model of myocardial electromechanics that accounts for two components of myocardial conductivity and delayed strain‐dependent changes in membrane capacitance that causes a conduction slowing. Two scenarios were simulated in 2D numerical experiments: (i) propagation of an excitation–contraction wave beyond the edge of a nonconductive nonexcitable obstacle; (ii) circulation of a re‐entry wave around a nonconductive nonexcitable obstacle. The simulations demonstrated that the delayed strain‐dependent deceleration of the conduction waves promotes the detachment of the excitation‐contraction waves from the sharp edge of an elongated obstacle and modulates the re‐entry waves rotating around a compact obstacle. The data show that the mechano‐electrical feedback, together with an increase in the stimulation frequency and an increase in the excitation threshold, is an arrhythmogenic factor that must be taken into account when analyzing the possibility of the re‐entry formation. [ABSTRACT FROM AUTHOR]

Cigarette smoke exposure is a well-known risk factor for developing numerous chronic health conditions, including pulmonary disease and cardiometabolic disorders. However, the cellular mechanisms mediating the toxicity of cigarette smoke in extrapulmonary tissues are still poorly understood. Therefore, the purpose of this study was to characterize the acute dose-dependent toxicity of cigarette smoke on mitochondrial metabolism by determining the susceptibility and sensitivity of mitochondrial respiration from murine skeletal (gastrocnemius and soleus) and cardiac muscles, as well as the aorta to cigarette smoke concentrate (CSC). In all tissues, exposure to CSC inhibited tissue-specific respiration capacity, measured by high-resolution respirometry, according to a biphasic pattern. With a break point of 451 ± 235 µg/mL, the aorta was the least susceptible to CSC-induced mitochondrial respiration inhibition compared with the gastrocnemius (151 ± 109 µg/mL; P = 0.008, d = 2.3), soleus (211 ± 107 µg/mL; P = 0.112; d = 1.7), and heart (94 ± 51 µg/mL; P < 0.001; d = 2.6) suggesting an intrinsic resistance of the vascular smooth muscle mitochondria to cigarette smoke toxicity. In contrast, the cardiac muscle was the most susceptible and sensitive to the effects of CSC, demonstrating the greatest decline in tissue-specific respiration with increasing CSC concentration (P < 0.001, except the soleus). However, when normalized to citrate synthase activity to account for differences in mitochondrial content, cardiac fibers' sensitivity to cigarette smoke inhibition was no longer significantly different from both fast-twitch gastrocnemius and slow-twitch soleus muscle fibers, thus suggesting similar mitochondrial phenotypes. Collectively, these findings established the acute dosedependent toxicity of cigarette smoke on oxidative phosphorylation in permeabilized tissues involved in the development of smoke-related cardiometabolic diseases. [ABSTRACT FROM AUTHOR]

Dilated cardiomyopathy (DCM) is a life-threatening form of heart disease that is typically characterized by progressive thinning of the ventricular walls, chamber dilation, and systolic dysfunction. Multiple mutations in the gene encoding filamin C (FLNC), an actin-binding cytoskeletal protein in cardiomyocytes, have been found in patients with DCM. However, the mechanisms that lead to contractile impairment and DCM in patients with FLNC variants are poorly understood. To determine how FLNC regulates systolic force transmission and DCM remodeling, we used an inducible, cardiac-specific FLNC-knockout (icKO) model to produce a rapid onset of DCM in adult mice. Loss of FLNC reduced systolic force development in single cardiomyocytes and isolated papillary muscles but did not affect twitch kinetics or calcium transients. Electron and immunofluorescence microscopy showed significant defects in Z-disk alignment in icKO mice and altered myofilament lattice geometry. Moreover, a loss of FLNC induces a softening myocyte cortex and structural adaptations at the subcellular level that contribute to disrupted longitudinal force production during contraction. Spatially explicit computational models showed that these structural defects could be explained by a loss of inter-myofibril elastic coupling at the Z-disk. Our work identifies FLNC as a key regulator of the multiscale ultrastructure of cardiomyocytes and therefore plays an important role in maintaining systolic mechanotransmission pathways, the dysfunction of which may be key in driving progressive DCM.

Simple Summary: Horses participating in cross-country tests are subjected to high physical stress. In this study, the blood values of 20 horses were examined before and after cross-country rides. The aim was to determine whether blood-based markers of muscle function change after cross-country rides. Parameters that provide information about fluid balance, muscle enzymes, metabolites and cardiac muscle-specific markers were investigated. We developed an approach to eliminate the concentration changes caused by shifts in fluid balance. Parameters were measured before, 10 and 30 min after exercise and the next morning and were evaluated using a mixed model. At 30 min post exercise, most parameter concentrations changed in an exercise-dependent manner. The next morning, most exercise-dependent markers recovered rapidly; creatine kinase (CK) (26% increase; p = 0.008) and lactate dehydrogenase (LDH) (15% increase; p < 0.001) showed a declining but sustained increase. Cardiac troponin I (cTnI) increased above the reference range in 40 of the 55 rides (73%) and in 18 of 20 horses in the morning after exercise. Horses competing in cross-country tests are subjected to high physical demands. Within the scope of this prospective longitudinal study, blood values of 20 elite eventing horses were examined before and after two- to four-star cross-country rides. The aim was to find out whether blood-based markers for skeletal muscle and cardiac muscle function change after cross-country exercise. Parameters that provide information about fluid balance, muscle enzymes, metabolites and cardiac muscle-specific markers were investigated. We developed an approach to eliminate the concentration changes caused by reduced plasma volume. Parameters were measured pre, 10 and 30 min post exercise and the next morning and were evaluated using a mixed model. Thirty minutes after exercise, most parameter concentrations changed in an exercise-dependent manner. The next morning, most exercise-related markers recovered rapidly, while creatine kinase (CK) (26% increase; p = 0.008) and lactate dehydrogenase (LDH) (15% increase; p < 0.001) showed a declining but sustained increase. Cardiac troponin I (cTnI) increased above the reference range in 40 of the 55 rides (73%) and in 18 of 20 horses in the morning after exercise. [ABSTRACT FROM AUTHOR]

Current pharmacological options for hypertrophic cardiomyopathy (HCM) are not disease-specific; while it treats symptoms, mavacamten targets the underlying pathology. We aim to assess the efficacy and safety of mavacamten, a first-in-class cardiac myosin inhibitor, in symptomatic obstructive HCM. This systematic review of the literature followed the PRISMA guidelines. Title/abstract and topics were searched using the following term: "mavacamten". The electronic research literature databases included the Cochrane Library, MedLine, and clinicaltrials.gov from July to August 2022. Primary efficacy endpoint was to assess clinical response at the end of treatment compared with baseline, defined as, at least one New York Heart Association (NYHA) class reduction. Two secondary endpoints from baseline were determined. The first was defined as improvement in mixed venous oxygen pressure (pVO 2). The second was defined as reduction of the post-exercise left ventricular outflow tract (LVOT) gradient. We included in our analyses data from four studies that met our review eligibility criteria. There were three randomised placebo-controlled clinical trials and one non-randomised open-label clinical trial. All four studies showed a reduction in NYHA class from mavacamten use. Three out of four studies demonstrated >1 NYHA functional class improvement ranging from 34% to 80%, while only one study showed a smaller percentage of patients remaining at class 3. Three out of four studies measured pVO 2 as an outcome, and all three studies noticed an increase in peak oxygen consumption after mavacamten treatment. Additionally, three out of four studies measured post-exercise LVOT gradient reduction as an outcome and all three found significant reduction in the post-exercise LVOT gradient after treatment. The most commonly observed adverse side effects were atrial fibrillation and decreased left ventricular ejection fraction, but all participants recovered without long-term sequelae and only one patient dropped out of the trial. Mavacamten has a greater efficacy than placebo in the treatment of HCM. It also showed promising tolerability and efficacy profiles in the treatment of HCM in adults. The three endpoints used in the evaluation of studies were reduction in NYHA class, increase in pVO 2 , and post-exercise LVOT gradient reduction. Mavacamten showed greater reduction in NYHA, larger effects on increase of pVO 2 , and significant reduction of the LVOT gradient. Mavacamten was also found to be well tolerated, like the placebo. The side effect profile was limited for the majority of individuals taking mavacamten. In the future, authors recommended dose-optimisation studies, and studies that evaluate mavacamten both in comparison to, and in conjunction with other current treatments. [ABSTRACT FROM AUTHOR]

Phthalates are common plasticizers present in medical-grade plastics and other everyday products. Di-ethylhexyl phthalate (DEHP) has been noted as a causative risk factor for the initiation and augmentation of cardiovascular functional disorders. G-CSF is a glycoprotein found in numerous tissues throughout the body and is currently applied in clinical practice and has been tested in congestive heart failure. We aimed to examine in depth the effect of DEHP on the histological and biochemical structure of the cardiac muscle in adult male albino rats and the mechanisms underlying the possible ameliorative effect of G-CSF. Forty-eight adult male albino rats were divided into control group, DEHP group, DEHP+ G-CSF group and DEHP-recovery group. We measured serum levels of aspartate aminotransferase (AST), creatine kinase MB isoenzyme (CK-MB) and lactate dehydrogenase (LDH). Left ventricular sections were processed for light and electron microscope examination, and immunohistochemical staining of Desmin, activated Caspase-3 and CD34. DEHP significantly increased enzyme levels, markedly distorted the normal architecture of cardiac muscle fibers, downregulated Desmin protein levels and enhanced fibrosis, and apoptosis. G-CSF treatment significantly decreased the enzyme levels compared to DEHP group. It enhanced CD34 positive stem cells recruitment to injured cardiac muscle, therefore improved the ultrastructural features of most cardiac muscle fibers via anti-fibrotic and anti-apoptotic effects in addition to increased Desmin protein expression levels. The recovery group showed partial improvement due to persistent DEHP effect. In conclusion, administration of G-CSF effectively corrected the histopathological, immunohistochemical and biochemical alterations in the cardiac muscle after DEHP administration by stem cells recruitment, Desmin protein regulation, antifibrotic and antiapoptotic mechanisms. [ABSTRACT FROM AUTHOR]

Background and objective: In this present research paper, a mathematical model has been developed to study myocyte contraction in the human cardiac muscle, using the Land model. Different parts of the human heart with a focus on the composition of the myocyte cells have been explored numerically to enabling us to determine the interaction of various parameters in the heart muscle. The main objective of the work is to direct the study of the Land model, which has been exploited to simulate the contraction of real human myocytes. Methods: Mathematical models has been developed based on the Hill model and Huxley model. Myocyte contraction for different scenarios, such as in isometric tension and isotonic tension have been studied. Results: It is found that increase in stretch, the peak active tension increases, in line with well-established length-dependent tension generation. Five parameters are selected: [Ca2+]T50, Tref, TRPN50, β0, and β1, which have been varied in between the range of −50%–100%, to examine the isometric effects of each parameter on the behavior of the tension developed in the intact myocyte cells, with the most sensitive parameter being [Ca2+]T50. Conclusion: In conclusion, it is found that the Land model provides a good platform for the analysis of the active contraction of the human cardiac myocyte.

Recent work on high‐performance lower‐field MR systems has renewed the interest in assessing relative advantages and disadvantages of magnetic fields less than 1 T. The objective of the present work was to investigate signal‐to‐noise ratio (SNR) scaling of point‐resolved spectroscopy as a function of field strength and to test the feasibility of proton MRS of triglycerides (TGs) in human in vivo myocardium at 0.75 T relative to 1.5 T and 3 T. Measurements at 0.75 T were obtained by temporarily ramping down a clinical 3 T MR scanner. System configurations at 0.75, 1.5 and 3 T featured identical hard‐ and software, except for differences in transmit/receive coil geometries and receive channel count, which were accounted for in SNR comparisons. Proton MRS was performed at 0.75 T, 1.5 T and 3 T in ex vivo tissue and in vivo calf muscle to measure T1 and T2 values as a function of field strength, which in turn served as input to simulations of SNR scaling and field‐dependent TG fit errors. Preliminary in vivo spectra of myocardium were acquired at 0.75 T, 1.5 T and 3 T in healthy subjects. Measurements of both ex vivo tissue and in vivo muscle tissue at 0.75 T versus 1.5 T and 3 T confirmed decreasing T1 and increasing T2* for decreasing field strengths. Using measured T1, T2 and T2* as input and using field‐dependent echo time and bandwidth scaling, simulated Cramér‐Rao lower bounds of TG amplitudes at 0.75 T were 2.3 and 4.5 times larger with respect to 1.5 T and 3 T, respectively. In vivo measurements demonstrate that human proton spectroscopy of TGs in cardiac muscle is feasible at 0.75 T, supporting the potential practical value of lower‐field high‐performance MR systems. [ABSTRACT FROM AUTHOR]

Molecularly imprinted polymers (MIPs) are synthetic polymers with specific binding sites that present high affinity and spatial and chemical complementarities to a targeted analyte. They mimic the molecular recognition seen naturally in the antibody/antigen complementarity. Because of their specificity, MIPs can be included in sensors as a recognition element coupled to a transducer part that converts the interaction of MIP/analyte into a quantifiable signal. Such sensors have important applications in the biomedical field in diagnosis and drug discovery, and are a necessary complement of tissue engineering for analyzing the functionalities of the engineered tissues. Therefore, in this review, we provide an overview of MIP sensors that have been used for the detection of skeletal- and cardiac-muscle-related analytes. We organized this review by targeted analytes in alphabetical order. Thus, after an introduction to the fabrication of MIPs, we highlight different types of MIP sensors with an emphasis on recent works and show their great diversity, their fabrication, their linear range for a given analyte, their limit of detection (LOD), specificity, and reproducibility. We conclude the review with future developments and perspectives. [ABSTRACT FROM AUTHOR]

Mitochondrial health declines with age, and older patients can demonstrate dysfunction in mitochondrial-rich tissues, such as cardiac and skeletal muscle. Aged mitochondria may make older adults more susceptible to adverse drug reactions (ADRs). We assessed mitochondrial metabolic function by measuring two metabolites, l-carnitine and acetylcarnitine, to determine their effectiveness as candidate clinical biomarkers for age-related, drug-induced alterations in mitochondrial metabolism. To study age- and medication-related changes in mitochondrial metabolism, we administered the FDA-approved mitochondriotropic drug, clofazimine (CFZ), or vehicle for 8 weeks to young (4-week-old) and old (61-week-old) male C57BL/6J mice. At the end of treatment, whole blood and cardiac and skeletal muscle were analyzed for l-carnitine, acetylcarnitine, and CFZ levels; muscle function was measured via a treadmill test. No differences were found in blood or cardiac carnitine levels of CFZ-treated mice, but CFZ-treated mice displayed lost body mass and alterations in endurance and levels of skeletal muscle mitochondrial metabolites. These findings demonstrate the age-related susceptibility of the skeletal muscle to mitochondria drug toxicity. Since drug-induced alterations in mitochondrial metabolism in skeletal muscle were not reflected in the blood by l-carnitine or acetylcarnitine levels, drug-induced catabolism and changes in muscle function appear more relevant to stratifying individuals at increased risk for ADRs. [ABSTRACT FROM AUTHOR]

Cardiac excitation-contraction (E-C) coupling is influenced by (at least) three dynamic systems that couple and feedback to one another (see Abstract Figure). Here we review the mechanical effects on cardiomyocytes that include mechano-electro-transduction (commonly referred to as mechano-electric coupling, MEC) and mechano-chemo-transduction (MCT) mechanisms at cell and molecular levels which couple to Ca2+ -electro and E-C coupling reviewed elsewhere. These feedback loops from muscle contraction and mechano-transduction to the Ca2+ homeodynamics and to the electrical excitation are essential for understanding the E-C coupling dynamic system and arrhythmogenesis in mechanically loaded hearts. This white paper comprises two parts, each reflecting key aspects from the 2018 UC Davis symposium: MEC (how mechanical load influences electrical dynamics) and MCT (how mechanical load alters cell signalling and Ca2+ dynamics). Of course, such separation is artificial since Ca2+ dynamics profoundly affect ion channels and electrogenic transporters and vice versa. In time, these dynamic systems and their interactions must become fully integrated, and that should be a goal for a comprehensive understanding of how mechanical load influences cell signalling, Ca2+ homeodynamics and electrical dynamics. In this white paper we emphasize current understanding, consensus, controversies and the pressing issues for future investigations. Space constraints make it impossible to cover all relevant articles in the field, so we will focus on the topics discussed at the symposium.

Rhesus macaques are physiologically similar to humans and, thus, have served as useful animal models of human diseases including cardiovascular disease. The purpose of this study was to characterize the distribution, composition, and phenotype of macrophages in heart tissues of very young (fetus: 0.5 years, n = 6), young adult (2-12 years, n = 12), and older adult (13-24 years, n = 9) rhesus macaques using histopathology and immunofluorescence microscopy. Results demonstrated that macrophages were uniformly distributed throughout the heart in animals of all age groups and were more prevalent than CD3-positve T-cells and CD20-positive B-cells. Macrophages comprised approximately 2% of heart tissue cells in the younger animals and increased to a mean of nearly 4% in the older adults. CD163-positive macrophages predominated over HAM56-positive and CD206-positive macrophages, and were detected at significantly higher percentage in the animals between 13 and 24 years of age, as well as in heart tissues exhibiting severe histopathology or inflammation in animals of all age groups. In vivo dextran labeling and retention indicated that approximately half of the macrophages were longer lived in healthy adult heart tissues and may comprise the tissue-resident population of macrophages. These results provide a basis for continued studies to examine the specific functional roles of macrophage subpopulations in heart tissues during homeostasis and in cardiovascular disease for then developing intervention strategies.

Dantrolene is an intra-cellularly acting skeletal muscle relaxant used for the treatment of the rare genetic disorder, malignant hyperthermia (MH). In most cases, MH susceptibility is caused by dysfunction of the skeletal ryanodine receptor (RyR1) harboring one of nearly 230 single-point MH mutations. The therapeutic effect of dantrolene is the result of a direct inhibitory action on the RyR1 channel, thus suppressing aberrant Ca2+ release from the sarcoplasmic reticulum. Despite the almost identical dantrolene-binding sequence exits in all three mammalian RyR isoforms, dantrolene appears to be an isoform-selective inhibitor. Whereas RyR1 and RyR3 channels are competent to bind dantrolene, the RyR2 channel, predominantly expressed in the heart, is unresponsive. However, a large body of evidence suggests that the RyR2 channel becomes sensitive to dantrolene-mediated inhibition under certain pathological conditions. Although a consistent picture of the dantrolene effect emerges from in vivo studies, in vitro results are often contradictory. Hence, our goal in this perspective is to provide the best possible clues to the molecular mechanism of dantrolene's action on RyR isoforms by identifying and discussing potential sources of conflicting results, mainly coming from cell-free experiments. Moreover, we propose that, specifically in the case of the RyR2 channel, its phosphorylation could be implicated in acquiring the channel responsiveness to dantrolene inhibition, interpreting functional findings in the structural context. [ABSTRACT FROM AUTHOR]

Background: The rapidly increasing applications of zinc oxide nanoparticles (ZnO NPs) in various industries have led to growing concerns about their damaging influence on human health. The present research was designed to determine the protective action of vitamins (Vits) A, C and E on the heart toxicity induced by ZnO NPs. Methods: Fifty-four male Wistar rats were allocated into 9 groups of 6 and then exposed to ZnO NPs (200 mg/kg), water (Control1), olive oil (Control2), Vit A (1000 IU/kg), Vit C (200 mg/kg), Vit E (100 IU/kg) and three groups were co-treated with ZnO and one of the Vits A, C or E. The oxidative stress situation was evaluated by measuring oxidative stress markers and the tissue antioxidant enzyme activity. Besides, the mRNA expression of Bcl-2 and Bax and caspase 3,7 activity were assessed. A histopathological examination was also performed to determine the rate of cardiac injury. Results: The results indicated that co-administration of ZnO NPs and the aforementioned Vits significantly reduced the total oxidant status and lipid peroxidation relative to the ZnO group (P < 0.05). Furthermore, the supplementation of vitamins, notably Vit E, decreased the ZnO NPs-induced oxidative damage by enhancing the activity of antioxidant enzymes compared to the ZnO NPs-fed rats (P < 0.05). Data also showed the mitigating effects of Vits against ZnO NPs-mediated apoptosis by suppressing the ratio of Bax/Bcl-2 expression and caspase 3,7 activity. Conclusion: This study highlights the protective role of Vits A, C and E against ZnO NPs cardiotoxicity, though at different levels of effectiveness. [ABSTRACT FROM AUTHOR]

Impaired calcium uptake resulting from reduced expression and activity of the cardiac sarco-endoplasmic reticulum Ca2+ ATPase (SERCA2a) is a hallmark of heart failure (HF). Recently, new mechanisms of SERCA2a regulation, including post-translational modifications (PTMs), have emerged. Our latest analysis of SERCA2a PTMs has identified lysine acetylation as another PTM which might play a significant role in regulating SERCA2a activity. SERCA2a is acetylated, and that acetylation is more prominent in failing human hearts. In this study, we confirmed that p300 interacts with and acetylates SERCA2a in cardiac tissues. Several lysine residues in SERCA2a modulated by p300 were identified using in vitro acetylation assay. Analysis of in vitro acetylated SERCA2a revealed several lysine residues in SERCA2a susceptible to acetylation by p300. Among them, SERCA2a Lys514 (K514) was confirmed to be essential for SERCA2a activity and stability using an acetylated mimicking mutant. Finally, the reintroduction of an acetyl-mimicking mutant of SERCA2a (K514Q) into SERCA2 knockout cardiomyocytes resulted in deteriorated cardiomyocyte function. Taken together, our data demonstrated that p300-mediated acetylation of SERCA2a is a critical PTM that decreases the pump's function and contributes to cardiac impairment in HF. SERCA2a acetylation can be targeted for therapeutic aims for the treatment of HF. [ABSTRACT FROM AUTHOR]

Membrane contact sites between endoplasmic reticulum (ER) and plasma membrane (PM), or ER-PM junctions, are found in all eukaryotic cells. In excitable cells they play unique roles in organizing diverse forms of Ca2+ signaling as triggered by membrane depolarization. ER-PM junctions underlie crucial physiological processes such as excitation-contraction coupling, smooth muscle contraction and relaxation, and various forms of activity-dependent signaling and plasticity in neurons. In many cases the structure and molecular composition of ER-PM junctions in excitable cells comprise important regulatory feedback loops linking depolarization-induced Ca2+ signaling at these sites to the regulation of membrane potential. Here, we describe recent findings on physiological roles and molecular composition of native ER-PM junctions in excitable cells. We focus on recent studies that provide new insights into canonical forms of depolarization-induced Ca2+ signaling occurring at junctional triads and dyads of striated muscle, as well as the diversity of ER-PM junctions in these cells and in smooth muscle and neurons. [ABSTRACT FROM AUTHOR]

During ischemic heart failure (IHF), cardiac muscle contraction is typically impaired, though the molecular changes within the myocardium are not fully understood. Thus, we aimed to characterize the biophysical properties of cardiac myosin in IHF. Cardiac tissue was harvested from 10 age-matched males, either with a history of IHF or nonfailing (NF) controls that had no history of structural or functional cardiac abnormalities. Clinical measures before cardiac biopsy demonstrated significant differences in measures of ejection fraction and left ventricular dimensions. Myofibrils and myosin were extracted from left ventricular free wall cardiac samples. There were no changes in myofibrillar ATPase activity or calcium sensitivity between groups. Using isolated myosin, we found a 15% reduction in the IHF group in actin sliding velocity in the in vitro motility assay, which was observed in the absence of a myosin isoform shift. Oxidative damage (carbonylation) of isolated myosin was compared, in which there were no significant differences between groups. Synthetic thick filaments were formed from purified myosin and the ATPase activity was similar in both basal and actin-activated conditions (20 mM actin). Correlation analysis and Deming linear regression were performed between all studied parameters, in which we found statistically significant correlations between clinical measures of contractility with molecular measures of sliding velocity and ELC carbonylation. Our data indicate that subtle deficits in myosin mechanochemical properties are associated with reduced contractile function and pathological remodeling of the heart, suggesting that the myosin motor may be an effective pharmacological intervention in ischemia. [ABSTRACT FROM AUTHOR]

Background: Energy drinks are non-alcoholic beverages containing mainly caffeine. Chronic consumption of energy drinks may be associated with increased blood pressure, and cardiac work load, as well as, increased heart rate. Energy drinks consumption has been related to myocardial infarction in healthy young adult. Aim of the Work: The aim of the present work was to study the harmful effect of energy drinks histologically and morphometrically, on the myocardium of the adult male albino rats. Material and Methods: 20 Adult male albino rats aging 4-6 moths were divided randomly into two groups; Group I (Control group) which consisted of 10 male albino rats with free access to food (rat chew) and water and Group II (Experimental group): 10 male albino rats which received 3.75 ml/kg body weight red bull through oral gavage daily for 4 weeks with free access to food (rat chew) and water. At the end of experiment, rats were-scarificed, and cardiac muscle was extracted and processed into paraffin blocks for light microscopic examination. Morphometric study and statistical analysis were done. Results: The present work demonstrated that Red Bull induced several histopathological changes of the cardiac muscle. The results showed the cardiac muscle of rats with irregularities in the arrangement of fibers and wide spaces in between. Some cardiomyocytes showed areas of pale stained sarcoplasm, partial loss of the cross striations and ill-defined intercalated discs. Localized areas of hyaline degeneration and areas of tissue disruption were also noticed with less frequently localized coalesced cytoplasmic vacuoles. The nuclei of the cardiomyocytes appeared small, darkly stained, and pyknotic. Others were flattened and deeply stained. Congested, and thick walled blood vessels were also observed, with mononuclear cellular infiltrations. In Masson's Trichrome sections, relative increase in collagen deposition between the cardiac muscle fibers was observed which was associated with focal fibrous degeneration. Examination of the semithin sections showed partial disruption of the cardiomyocytes. The nuclei of the cardiomyocytes were small, darkly stained with perinuclear degeneration. Some nuclei were eccentric, or with an irregular outline, and peripheral chromatin condensation. The characteristic finding was the presence of longitudinal wavy cardiac muscle fibers with relatively wide spaces in between and localized areas of partially lost cross striations and intercalated discs. Dilated, thick walled blood vessels was noticed between the bundles of cardiac muscle. Mononuclear inflammatory cellular infiltrations were also detected. Conclusion: The present study demonstrated the degenerative and cardiotoxic effects of Red Bull as an example of energy drinks on the histological structure of the cardiac muscle. [ABSTRACT FROM AUTHOR]

After years of intense research using structural, biological, and biochemical experimental procedures, it is clear that myosin molecules are essential for striated muscle contraction. However, this is just the tip of the iceberg of their function. Interestingly, it has been shown recently that these molecules (especially myosin heavy chains) are also crucial for cardiac and skeletal muscle resting state. In the present review, we first overview myosin heavy chain biochemical states and how they influence the consumption of ATP. We then detail how neighboring partner proteins including myosin light chains and myosin binding protein C intervene in such processes, modulating the ATP demand in health and disease. Finally, we present current experimental drugs targeting myosin ATP consumption and how they can treat muscle diseases. [ABSTRACT FROM AUTHOR]

The cardiac sarcomere is a triumph of biological evolution wherein myriad contractile and regulatory proteins assemble into a quasi-crystalline lattice to serve as the central point upon which cardiac muscle contraction occurs. This review focuses on the many signaling components and mechanisms of regulation that impact cardiac sarcomere function. We highlight the roles of the thick and thin filament, both as necessary structural and regulatory building blocks of the sarcomere as well as targets of functionally impactful modifications. Currently, a new focus emerging in the field is inter-myofilament signaling, and we discuss here the important mediators of this mechanism, including myosin-binding protein C and titin. As the understanding of sarcomere signaling advances, so do the methods with which it is studied. This is reviewed here through discussion of recent live muscle systems in which the sarcomere can be studied under intact, physiologically relevant conditions. [ABSTRACT FROM AUTHOR]

The sarco/endoplasmic reticulum Ca-ATPase (SERCA) is a P-type ion pump that transports Ca2+ from the cytosol into the endoplasmic/sarcoplasmic reticulum (ER/SR) in most mammalian cells. It is critically important in muscle, facilitating relaxation and enabling subsequent contraction. Increasing SERCA expression or specific activity can alleviate muscle dysfunction, most notably in the heart, and we seek to develop small-molecule drug candidates that activate SERCA. Therefore, we adapted an NADH-coupled assay, measuring Ca-dependent ATPase activity of SERCA, to high-throughput screening (HTS) format, and screened a 46,000-compound library of diverse chemical scaffolds. This HTS platform yielded numerous hits that reproducibly alter SERCA Ca-ATPase activity, with few false positives. The top 19 activating hits were further tested for effects on both Ca-ATPase and Ca2+ transport, in both cardiac and skeletal SR. Nearly all hits increased Ca2+ uptake in both cardiac and skeletal SR, with some showing isoform specificity. Furthermore, dual analysis of both activities identified compounds with a range of effects on Ca2+-uptake and ATPase, which fit into distinct classifications. Further study will be needed to identify which classifications are best suited for therapeutic use. These results reinforce the need for robust secondary assays and criteria for selection of lead compounds, before undergoing HTS on a larger scale. [ABSTRACT FROM AUTHOR]