Content In Myocytes Research Articles

Similarities and differences in morphology, CD31 and CD68 expression of male vs. female sinoatrial node and its surrounding atrial muscle in ageing and obesity

Similarities and differences in morphology, CD31 and CD68 expression of male vs. female sinoatrial node and its surrounding atrial muscle in ageing and obesity

Seipin Deficiency Accelerates Heart Failure Due to Calcium Handling Abnormalities and Endoplasmic Reticulum Stress in Mice

Seipin deficiency can induce hypertrophic cardiomyopathy and heart failure, which often leads to death in humans. To explore the effects and the possible mechanisms of Seipin deficiency in myocardial remodeling, Seipin knockout (SKO) mice underwent transverse aortic constriction (TAC) for 12 weeks. We found a more severe left ventricular hypertrophy and diastolic heart failure and increases in inflammatory cell infiltration, collagen deposition, and apoptotic bodies in the SKO group compared to those in the wild type (WT) group after TAC. Electron microscopy also showed a more extensive sarcoplasmic reticulum expansion, deformation of microtubules, and formation of mitochondrial lesions in the cardiomyocytes of SKO mice than in those of WT mice after TAC. Compared with the WT group, the SKO group showed increases in endoplasmic reticulum (ER) stress-, inflammation-, and fibrosis-related gene expression, while calcium ion-related factors, such as Serca2a and Ryr, were decreased in the SKO group after TAC. Increased levels of the ER stress-related protein GRP78 and decreased SERCA2a and P-RYR protein levels were detected in the SKO group compared with the WT group after TAC. Slowing of transient Ca2+ current decay and an increased SR Ca2+ content in myocytes were detected in the cardiomyocytes of SKO mice. Adipose tissue transplantation could not rescue the cardiac hypertrophy after TAC in SKO mice. In conclusion, we found that Seipin deficiency could promote cardiac hypertrophy and diastolic heart failure after TAC in mice. These changes may be related to the impairment of myocardial calcium handling, ER stress, inflammation, and apoptosis.

Mitochondrial Content, but Not Function, Is Altered With a Multimodal Resistance Training Protocol and Adequate Protein Intake in Leucine-Supplemented Pre/Frail Women.

Background: Frailty is a clinical condition associated with loss of muscle mass and strength (sarcopenia). Mitochondria are centrally implicated in frailty and sarcopenia. Leucine (Leu) can alter mitochondrial content in myocytes, while resistance training (RT) is the strongest stimulus to counteract sarcopenia and may enhance mitochondrial biogenesis.Objective: We determined the effects of Leu supplementation and RT on mitochondrial content and function in pre/frail elderly women in a randomized double-blinded placebo-controlled study.Methods: Nineteen pre/frail elderly women (77.5 ± 1.3 y, BMI: 25.1 ± 0.9 kg/m2), based on the Frailty Phenotype, underwent 3-months of RT 3×/week with protein-optimized diet and were randomized to 7.5 g/d of Leu supplementation or placebo alanine (Ala). Pre/post-intervention mitochondrial respiration, reactive oxygen species (ROS) production, calcium retention capacity (CRC), time to permeability transition pore (mPTP) opening, mitochondrial voltage-dependent anion channel (VDAC) protein content, leg press 1-repetition maximum (1RM), and 6-min walk test (6MWT) were measured.Results: No time, supplementation, or interaction effects were observed for respiration, ROS, time to mPTP opening, and CRC. VDAC levels significantly increased in the Leu group post-intervention (p = 0.012). Both groups significantly increased leg press 1RM and 6MWT, with no effect of supplementation.Discussion: Leu supplementation with 3 months of RT increased mitochondrial content. Future studies should investigate if there is an increase in mitochondrial turnover or a shift in quality control (mitophagy) in leucine supplemented pre/frail elderly women who undergo 12 weeks of RT.Clinical Trial Registration: ClinicalTrials.gov, identifier: NCT01922167.

Role of molecular and metabolic defects in impaired performance of dystrophic skeletal muscles

There occurs a progressive weakness and wastage of skeletal muscle in different types of muscular dystrophy. The loss of muscle fibers in dystrophic muscle with impaired function is associated with leakage of intracellular enzymes, maldistribution of electrolyte content and metabolic defects in myocytes. Marked increases in the sarcolemma (SL) Na+-K+ ATPase and Ca2+/Mg2+-ecto ATPase activities, as well as depressions in the sarcoplasmic reticulum (SR) Ca2+-uptake and Ca2+-pump ATPase activities were seen in dystrophic muscles of a hamster model of myopathy. In addition, impaired mitochondrial oxidative phosphorylation and decrease in the high energy stores as a consequence of mitochondrial Ca2+-overload were observed in these myopathic hamsters. In some forms of muscular dystrophy, it has been shown that deficiency of dystrophin produces marked alterations in the SL permeability and promotes the occurrence of intracellular Ca2+-overload for inducing metabolic defects, activation of proteases and contractile abnormalities in dystrophic muscle. Increases in SR Ca2+-release channels, SL Na+-Ca2+ exchanger and SL store-operated Ca2+-channels have been reported to induce Ca2+-handling abnormalities in a mouse model of muscular dystrophy. Furthermore, alterations in lipid metabolism and development of oxidative stress have been suggested as mechanisms for subcellular remodeling and cellular damage in dystrophic muscle. Although, several therapeutic interventions including gene therapy are available, these treatments neither fully prevent the course of development of muscular disorder nor fully improve the function of dystrophic muscle. Thus, extensive reasearch work with some novel inhibitors of oxidative stress, SL Ca2+-entry systems such as store-operated Ca2+-channels, Na+-Ca2+ exchanger and Ca2+/Mg2+-ecto ATPase (Ca2+-gating mechanism), as well as SR Ca2+-release and Ca2+-pump systems needs to be carried out in combination of gene therapy for improved beneficial effects in muscular dystrophy.

K475E PRKAG2 Mutation: Cardiac Phenotype and Targeted Therapy Using Rapamycin

BackgroundWe identified a novel mutation (K475E) in PRKAG2, coding for protein kinase AMP‐activated non‐catalytic subunit γ2, during a 27‐week prenatal ultrasound. A hypertrophic cardiomyopathy (HCM) phenotype was later confirmed. We have demonstrated in vitro that the K475E mutation led to increases in cardiomyocytes size and area which can be reversed by rapamycin. We have developed transgenic mouse lines with cardiac‐specific expression of the human wild type (TgWT) or K475E mutant (TgK475E) PRKAG2. The TgK475E mice exhibit many human PRKAG2 HCM phenotypes, including cardiac hypertrophy, glycogen overload and sudden death.ObjectiveTo characterize K475E‐induced cardiac phenotype in vivo and develop a targeted therapy using mTOR inhibition strategy for PRKAG2 mutation‐induced HCM.MethodsCardiac hypertrophy was monitored and cardiac glycogen levels were measured at several developmental stages. Neonatal mice (2‐wk old) were treated daily with vehicle or rapamycin (2 mg/kg, ip) for 4 weeks. Cardiac function was monitored longitudinally by echocardiography.ResultsHypertrophy in TgK475E mice was confirmed. Histology revealed large vacuoles and high glycogen content in TgK475E myocytes throughout the ventricles. Echocardiography confirmed that LV mass dramatically increased in TgK475E mice starting from 5 weeks of age. Daily rapamycin treatment for 2 weeks dramatically decreased 1) cardiac hypertrophy and 2) glycogen overload in TgK475E mice. These beneficial effects of rapamycin were significantly tempered, however, when we switched to an alternative dosing regimen (one ip injection/3 days) of rapamycin.ConclusionThe new transgenic mouse model reflects the early onset phenotype of the K475E mutation‐induced HCM in humans. The mTOR signaling pathway is involved in K475E induced HCM. Moreover, the mTOR inhibition strategy as targeted therapy for PRKAG2 induced HCM is effective and should be studied further.Support or Funding InformationThis study was supported by NIH P30GM114750 and the Oh‐Zopfi Research Award, Women & Infant's Hospital.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A Novel PRKAG2 Mutation (K475E): Early‐Onset Cardiac Phenotype and Targeted Therapy

BackgroundMutations in PRKAG2 have been implicated in hypertrophic cardiomyopathy (HCM). We identified a novel PRKAG2 mutation, K475E, in a neonate with prenatal onset of HCM noted on a 27‐week prenatal ultrasound. We have demonstrated in vitro that K475E mutation led to increases in cardiomyocytes size and area which can be reversed by rapamycin.ObjectiveTo characterize K475E‐induced cardiac phenotype in vivo, we developed two new transgenic mouse lines with cardiac‐specific expression of the human wild type (TgWT) or K475E mutant (TgK475E) PRKAG2. The goal of this study was to explore the effectiveness of rapamycin for targeted therapy for PRKAG2 mutation‐induced HCM.MethodsHuman WT and K475E DNA constructs were inserted into a pBluescript vector with the mouse α‐myosin heavy chain promoter. Transgenic mice were established by pronucleus microinjection. Rapamycin was treated from two‐week to six‐aged mice. Cardiac hypertrophy was examined and cardiac function changes were monitored by echocardiography.ResultsHypertrophy in TgK475E mice was confirmed by their significant increases in heart weight/body weight and heart weight/tibial length ratios versus the non‐transgenic control and TgWT mice. Histology revealed large vacuoles and high glycogen content in TgK475E myocytes throughout the ventricles. Echocardiography confirmed that LV mass dramatically increased in TgK475E mice starting from 5 weeks of age. Rapamycin treatment dramatically decreased 1) the ratios of heart weight/body weight and heart weight/tibia length and 2) glycogen overload in TgK475E mice. Moreover, K475E mutation caused inhibition of AMPK which was rectified by rapamycin treatment.ConclusionThese results indicate the transgenic mouse model reflects the early onset phenotype of the K475E mutation‐induced HCM. The mTOR signaling pathway is involved in K475E induced HCM. Our study suggests that mTOR inhibition strategy as targeted therapy for PRKAG2 induced HCM is effective and should be studied further.Support or Funding Information1. NIH P30GM114750 2. Oh‐Zopfi Research Award, Women & Infant's Hospital, RI.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Highly variable contractile performance correlates with myocyte content in trabeculae from failing human hearts

Heart failure (HF) is defined by compromised contractile function and is associated with changes in excitation-contraction (EC) coupling and cardiomyocyte organisation. Tissue level changes often include fibrosis, while changes within cardiomyocytes often affect structures critical to EC coupling, including the ryanodine receptor (RyR), the associated protein junctophilin-2 (JPH2) and the transverse tubular system architecture. Using a novel approach, we aimed to directly correlate the influence of structural alterations with force development in ventricular trabeculae from failing human hearts. Trabeculae were excised from explanted human hearts in end-stage failure and immediately subjected to force measurements. Following functional experiments, each trabecula was fixed, sectioned and immuno-stained for structural investigations. Peak stress was highly variable between trabeculae from both within and between failing hearts and was strongly correlated with the cross-sectional area occupied by myocytes (MCSA), rather than total trabecula cross-sectional area. At the cellular level, myocytes exhibited extensive microtubule densification which was linked via JPH2 to time-to-peak stress. Trabeculae fractional MCSA variability was much higher than that in adjacent free wall samples. Together, these findings identify several structural parameters implicated in functional impairment in human HF and highlight the structural variability of ventricular trabeculae which should be considered when interpreting functional data.

Rhabdomyolysis-Associated Acute Kidney Injury With Normal Creatine Phosphokinase

Rhabdomyolysis is a syndrome characterized by the breakdown of skeletal muscle and leakage of intracellular myocyte contents, such as creatine phosphokinase (CPK) and myoglobin, into the interstitial space and plasma resulting in acute kidney injury (AKI). Elevated CPK of at least 5 times the upper limit of normal is an important diagnostic marker of Rhabdomyolysis. We present a case of rhabdomyolysis with severe AKI with a normal CPK at presentation. A 32-year-old man presented with acute respiratory failure and AKI after an overdose of recreational drugs. Urinalysis at presentation showed trace amounts of blood, identified as rare red blood cells under microscopy. CPK was 156 U/L at presentation. Workup for glomerulonephritis and vasculitis was negative. He was initiated on renal replacement therapy, and a kidney biopsy showed severe acute tubular injury with positive myoglobin casts. Supportive management and renal replacement therapy was provided, and renal function spontaneously improved after a few weeks. This is an uncommon clinical presentation of severe rhabdomyolysis complicated by AKI. This suggests that CPK alone may not be a sensitive marker for rhabdomyolysis-induced AKI in some cases.

Rhabdomyolysis: Heroin induced or HCV related

Abstract Rhabdomyolysis is defined as dissolution of skeletal muscle, manifested by the release of myocyte contents into the circulation. It is a well recognized complication of toxins, recreational drugs, and medications. We report a case of a 32 year old man, intravenous heroin abuser who took heroin 2 days before presentation. He presented with oliguria, tea colored urine and painful bilateral lower limb swelling. Evaluation revealed azotemia, dyselectrolytemia (hyperkalemia and hyponatremia), proteinuria and hematuria. Highly elevated serum lactate dehydrogenase and creatinine kinase led to the diagnosis of rhabdomyolysis and acute renal failure. The patient was managed with hydration and haemodialysis, following which he improved appreciably. Rhabdomyolysis in heroin addicts is caused by muscle ischemia, direct myotoxic effects of heroin, skeletal muscle vasoconstriction and immunologic reaction. The patient was also found to have concurrent hepatitis C virus infection (HCV). HCV is known to produce extrahepatic manifestations like myositis. Some studies have proved isolation of HCV RNA from perivascular infiltrative lymphocytes and skeletal muscle fibers, implying that HCV may decrease the threshold for muscle lysis. This case highlights the probable role of HCV in predisposing rhabdomyolysis in an illicit drug abuser, which has not been reported in Indian literature.

Novel approaches to targeting PDE3 in cardiovascular disease.

Inhibitors of PDE3, a family of dual-specificity cyclic nucleotide phosphodiesterases, are used clinically to increase cardiac contractility by raising intracellular cAMP content in cardiac myocytes and to reduce vascular resistance by increasing intracellular cGMP content in vascular smooth muscle myocytes. When used in the treatment of patients with heart failure, PDE3 inhibitors are effective in the acute setting but increase sudden cardiac death with long-term administration, possibly reflecting pro-apoptotic and pro-hypertrophic consequences of increased cAMP-mediated signaling in cardiac myocytes. cAMP-mediated signaling in cardiac myocytes is highly compartmentalized, and different phosphodiesterases, by controlling cAMP content in functionally discrete intracellular microcompartments, regulate different cAMP-mediated pathways. Four variants/isoforms of PDE3 (PDE3A1, PDE3A2, PDE3A3, and PDE3B) are expressed in cardiac myocytes, and new experimental results have demonstrated that these isoforms, which are differentially localized intracellularly through unique protein-protein interactions, control different physiologic responses. While the catalytic regions of these isoforms may be too similar to allow the catalytic activity of each isoform to be selectively inhibited, targeting their unique protein-protein interactions may allow desired responses to be elicited without the adverse consequences that limit the usefulness of existing PDE3 inhibitors.

The Function of Stromal Interaction Molecule 1 (STIM1) in Heart

Stromal interaction molecule 1 (STIM1), an ER/SR Ca2+ sensor, has been well described as an activator of store-operated calcium channel (SOCC) Orai1 or the equivalents, upon SR/ER (Sarco/endoplasmic reticulum) Ca2+ depletion in many cell types. In heart, however, we found that the canonical actions of STIM1 do not apply. For example, STIM1 appears to be organized in puncta and linear segments apparently at the junctional SR (jSR) whether or not the SR is loaded with Ca2+. In normal ventricular myocytes the mobility of STIM1 was not changed by SR Ca2+ load when evaluated by fluorescence recovery after photobleaching (FRAP). Furthermore, in ventricular myocytes, STIM1 function does not depend on Orai1 while in sinoatrial node (SAN) cells, it does. In the ventricular myocytes, we found that STIM1 binds to non-phosphorylated phospholamban, an endogenous inhibitor of SERCA2a (Sarco/endoplasmic reticulum Ca2+ ATPase). By this means increased STIM1 levels activate (or “dis-inhibit”) SERCA2a in ventricular myocytes. In the SAN cells, however, STIM1 is involved in SAN automaticity regulation through Orai1 (and possibly by other means). Consistent with these findings, STIM1 null cells show decreased SR Ca2+ content in SAN and STIM1 overexpressing cells show increased SR Ca2+ content in ventricular myocytes. We therefore conclude that in heart, STIM1 contributes to the regulation of SR Ca2+ content through binding to different partners (including Orai1 and phospholamban) in ventricular myocytes and SAN. The kinetics and more complete physiological and pathophysiological influences of STIM1 on SR Ca2+ content in heart are under active investigation.

R4496C RyR2 mutation impairs atrial and ventricular contractility

Ryanodine receptor (RyR2) is the major Ca(2+) channel of the cardiac sarcoplasmic reticulum (SR) and plays a crucial role in the generation of myocardial force. Changes in RyR2 gating properties and resulting increases in its open probability (Po) are associated with Ca(2+) leakage from the SR and arrhythmias; however, the effects of RyR2 dysfunction on myocardial contractility are unknown. Here, we investigated the possibility that a RyR2 mutation associated with catecholaminergic polymorphic ventricular tachycardia, R4496C, affects the contractile function of atrial and ventricular myocardium. We measured isometric twitch tension in left ventricular and atrial trabeculae from wild-type mice and heterozygous transgenic mice carrying the R4496C RyR2 mutation and found that twitch force was comparable under baseline conditions (30°C, 2 mM [Ca(2+)]o, 1 Hz). However, the positive inotropic responses to high stimulation frequency, 0.1 µM isoproterenol, and 5 mM [Ca(2+)]o were decreased in R4496C trabeculae, as was post-rest potentiation. We investigated the mechanisms underlying inotropic insufficiency in R4496C muscles in single ventricular myocytes. Under baseline conditions, the amplitude of the Ca(2+) transient was normal, despite the reduced SR Ca(2+) content. Under inotropic challenge, however, R4496C myocytes were unable to boost the amplitude of Ca(2+) transients because they are incapable of properly increasing the amount of Ca(2+) stored in the SR because of a larger SR Ca(2+) leakage. Recovery of force in response to premature stimuli was faster in R4496C myocardium, despite the unchanged rates of recovery of L-type Ca(2+) channel current (ICa-L) and SR Ca(2+) content in single myocytes. A faster recovery from inactivation of the mutant R4496C channels could explain this behavior. In conclusion, changes in RyR2 channel gating associated with the R4496C mutation could be directly responsible for the alterations in both ventricular and atrial contractility. The increased RyR2 Po and fractional Ca(2+) release from the SR induced by the R4496C mutation preserves baseline contractility despite a slight decrease in SR Ca(2+) content, but cannot compensate for the inability to increase SR Ca(2+) content during inotropic challenge.

Irisin, a unique non-inflammatory myokine in stimulating skeletal muscle metabolism

Exercise offers several benefits for health, including increased lean body mass and heightened energy expenditure, which may be partially attributable to secretory factors known as myokines. Irisin, a recently identified myokine, was shown to increase metabolic rate and mitochondrial content in both myocytes and adipocytes; however, the mechanism(s) of action still remain largely unexplained. This work investigated if irisin functions by acting as an inflammatory myokine leading to cellular stress and energy expenditure. C2C12 myotubes were treated with various concentrations of irisin, TNFα, or IL6 for various durations. Glycolytic and oxidative metabolism, as well as mitochondrial uncoupling, were quantified by measurement of acidification and oxygen consumption, respectively. Metabolic gene and protein expression were measured by quantitative real-time polymerase chain reaction (qRT-PCR) and immunoblotting, respectively. Mitochondrial content was assessed by fluorescent imaging. NFκB activity was assessed using an NFκB GFP-linked reporter system. Consistent with previous findings, irisin significantly increased expression of several genes including peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) leading to increased mitochondrial content and oxygen consumption. Despite some similarities between TNFα and irisin treatment, irisin failed to activate the NFκB pathway like TNFα, suggesting that irisin may not act as an inflammatory signal. Irisin has several effects on myotube metabolism which appear to be dependent on substrate availability; however, the precise mechanism(s) by which irisin functions in skeletal muscle remain unclear. Our observations support the hypothesis that irisin does not function through inflammatory NFκB activation like other myokines (such as TNFα).

The Study of Synthesis, Accumulation and Release Processes of Atrial and Brain Natriuretic Peptides in Experimental Renovascular Hypertension

DOI: 10.17691/stm2015.7.2.04 Received November 10, 2014М.V. Galkina, PhD, Senior Researcher, Electron Microscopy unit, Central Scientific Research laboratory;О.s. baskina, PhD, Senior Researcher, Morphology Department, Central Scientific Research laboratory;М.L. bugrova, PhD, Associate Professor, Head of Electron Microscopy unit, Central Scientific Research laboratory Nizhny Novgorod State Medical Academy, 10/1 Minin and Pozharsky Square, Nizhny Novgorod, 603005, Russian federationThe aim of the investigation was to study the dynamics of synthesis, accumulation and release processes of atrial (ANP) and brain (BNP) natriuretic peptides on day 60 of experimental renovascular hypertension.Materials and Methods. The experiments were carried put on white non-pedigree male rats. we studied renovascular hypertension using a two-kidney model with the left renal artery ligation. Arterial pressure (AP) was measured via caudal artery using an invasive technique. we analyzed left ventricular cardiac myocyte areas by light optics. Electron microscopic investigation was applied to study the left ventricular and right atrial tissue samples. ANP and BNP accumulation and release processes were assessed using a quantitative analysis of immunolabeled granules of atrial myocytes (А-type, “mature, storing”, and B-type, “dissolving”) under the transmission electron microscope. we performed a morphometric analysis of morphological types of the left ventricular and right atrial mitochondria.Results. The number of granules containing ANP and BNP in atrial myocytes on day 60 after the left renal artery ligation in rats was found to be no significantly different from that in the intact group. we revealed AP decrease up to the initial level. ANP and BNP content in atrial myocytes and AP recovered against the background of cardiac myocyte hypertrophy, mitochondrial de-energization and destructive changes in microcirculatory bloodstream.Conclusion. In a long-term period of experimental renovascular hypertension, ANP and BNP have a positive effect on AP level falling up to the initial one due to ANP and BNP release on day 30 of the experiment. The efficiency of natriuretic peptides acting as a regulatory component in primary hypertension formation depends on arterial hypertension genesis.Key words: аtrial natriuretic peptide; brain natriuretic peptide; renovascular hypertension.For contacts: Galkina Maria Vladimirovna, e-mail: maryrax82@gmail.comAtrial and Brain Natriuretic Peptides in Experimental Renovascular Hypertension

VEGF165A microsphere therapy for myocardial infarction suppresses acute cytokine release and increases microvascular density but does not improve cardiac function.

Angiogenesis induced by growth factor-releasing microspheres can be an off-the-shelf and immediate alternative to stem cell therapy for acute myocardial infarction (AMI), independent of stem cell yield and comorbidity-induced dysfunction. Reliable and prolonged local delivery of intact proteins such as VEGF is, however, notoriously difficult. Our objective was to create a platform for local angiogenesis in human-sized hearts, using polyethylene-glycol/polybutylene-terephthalate (PEG-PBT) microsphere-based VEGF165A delivery. PEG-PBT microspheres were biocompatible, distribution was size dependent, and a regimen of 10 × 10(6) 15-μm microspheres at 0.5 × 10(6)/min did not induce cardiac necrosis. Efficacy, studied in a porcine model of AMI with reperfusion rather than chronic ischemia used for most reported VEGF studies, shows that microspheres were retained for at least 35 days. Acute VEGF165A release attenuated early cytokine release upon reperfusion and produced a dose-dependent increase in microvascular density at 5 wk following AMI. However, it did not improve major variables for global cardiac function, left ventricular dimensions, infarct size, or scar composition (collagen and myocyte content). Taken together, controlled VEGF165A delivery is safe, attenuates early cytokine release, and leads to a dose-dependent increase in microvascular density in the infarct zone but does not translate into changes in global or regional cardiac function and scar composition.

Hyperphosphorylation of RyRs underlies triggered activity in transgenic rabbit model of LQT2 syndrome.

Loss-of-function mutations in human ether go-go (HERG) potassium channels underlie long QT syndrome type 2 (LQT2) and are associated with fatal ventricular tachyarrhythmia. Previously, most studies focused on plasma membrane-related pathways involved in arrhythmogenesis in long QT syndrome, whereas proarrhythmic changes in intracellular Ca(2+) handling remained unexplored. We investigated the remodeling of Ca(2+) homeostasis in ventricular cardiomyocytes derived from transgenic rabbit model of LQT2 to determine whether these changes contribute to triggered activity in the form of early after depolarizations (EADs). Confocal Ca(2+) imaging revealed decrease in amplitude of Ca(2+) transients and sarcoplasmic reticulum Ca(2+) content in LQT2 myocytes. Experiments using sarcoplasmic reticulum-entrapped Ca(2+) indicator demonstrated enhanced ryanodine receptor (RyR)-mediated sarcoplasmic reticulum Ca(2+) leak in LQT2 cells. Western blot analyses showed increased phosphorylation of RyR in LQT2 myocytes versus controls. Coimmunoprecipitation experiments demonstrated loss of protein phosphatases type 1 and type 2 from the RyR complex. Stimulation of LQT2 cells with β-adrenergic agonist isoproterenol resulted in prolongation of the plateau of action potentials accompanied by aberrant Ca(2+) releases and EADs, which were abolished by inhibition of Ca(2+)/calmodulin-dependent protein kinase type 2. Computer simulations showed that late aberrant Ca(2+) releases caused by RyR hyperactivity promote EADs and underlie the enhanced triggered activity through increased forward mode of Na(+)/Ca(2+) exchanger type 1. Hyperactive, hyperphosphorylated RyRs because of reduced local phosphatase activity enhance triggered activity in LQT2 syndrome. EADs are promoted by aberrant RyR-mediated Ca(2+) releases that are present despite a reduction of sarcoplasmic reticulum content. Those releases increase forward mode Na(+)/Ca(2+) exchanger type 1, thereby slowing repolarization and enabling L-type Ca(2+) current reactivation.

Continuous renal replacement therapy (CRRT) for rhabdomyolysis

Rhabdomyolysis is a condition that is characterised by the breakdown of skeletal muscle tissue and leakage of intracellular myocyte contents into circulating blood. Rhabdomyolysis can lead to acute kidney injury (AKI) and is a potentially life-threatening condition. Studies have indicated that continuous renal replacement therapy (CRRT) may provide benefits for people with rhabdomyolysis by removing potentially damaging myoglobin and stabilising haemodynamic and metabolic status. We aimed to: i) assess the efficacy of CRRT in removing myoglobin; ii) investigate the influence of CRRT on mortality and kidney-related outcomes; and iii) evaluate the safety of CRRT for the treatment of people with rhabdomyolysis. We searched the Cochrane Renal Group's Specialised Register to 6 January 2014 through contact with the Trials' Search Co-ordinator using search terms relevant to this review. We also searched China National Knowledge Infrastructure (from 1 January 1979 to 16 April 2013) and the Chinese Clinical Trials Register (to 16 April 2013). All randomised controlled trials (RCTs) and quasi-RCTs that investigated clinical outcomes of CRRT for people with rhabdomyolysis were included. Two authors independently assessed studies for inclusion and extracted data. We derived risk ratios (RR) for dichotomous data and mean differences (MD) for continuous data with 95% confidence intervals (CI). Methodological risk of bias was assessed using the Cochrane risk of bias tool. Of the three included studies (101 participants), one evaluated continuous arteriovenous haemodialysis and two investigated continuous venovenous haemofiltration; all included conventional therapy as control.We found significant decreases in myoglobin in patients among whom CRRT therapy was initiated on days four, eight, and 10 (day 4: MD -11.00 (μg/L), 95% CI -20.65 to -1.35; Day 8: MD -23.00 (μg/L), 95% CI -30.92 to -15.08; day 10: MD -341.87 (μg/L), 95% CI -626.15 to -57.59) compared with those who underwent conventional therapy.Although CRRT was associated with improved serum creatinine, blood urea nitrogen, and potassium levels; reduced duration of the oliguria phase; and was associated with reduced time in hospital, no significant differences were found in mortality rates compared with conventional therapy (RR 0.17, 95% CI 0.02 to 1.37). The included studies did not report on long-term outcomes or prevention of AKI.Overall, we found that study quality was suboptimal: blinding and randomisation allocation were not reported by any of the included studies, leading to the possibility of selection, performance and detection bias. Although CRRT may provide some benefits for people with rhabdomyolysis, the poor methodological quality of the included studies and lack of data relating to clinically important outcomes limited our findings about the effectiveness of CRRT for people with rhabdomyolysis.There was insufficient evidence to discern any likely benefits of CRRT over conventional therapy for people with rhabdomyolysis and prevention of rhabdomyolysis-induced AKI.

Hypercholesterolemia Protects Against Ischemia-Induced Ventricular Tachycardia and Ventricular Fibrillation

Background:Membrane cholesterol regulates ion channels. Hypercholesterolemia protect against ventricular fibrillation in patients with myocardial infarction. Hypothesis: Hypercholesterolemia increases action potential duration due to altered ion channels function and protects against ischemia induced re-entrant arrhythmias.Methods:QTc intervals were measured in 10 week old LDL-receptor (LDLr-/-) and APO1 (APO1-/-) knockout mice, and wild type mice (WT). Action potentials, calcium handling and ion currents were recorded in ventricular myocytes. In perfused hearts regional ischemia was induced by ligating the left anterior descending artery . Arrhythmias inducibility was tested every 30 s by applying premature stimuli followed by a 500 ms pause. The area at risk (AAR) was determined by perfusion with Evans Blue.Results:Serum LDL cholesterol was higher in LDLr-/- and serum HDL cholesterol was lower in APO1-/- mice than in WT. Resulting in an increased cholesterol content in ventricular myocytes. The L-type calcium current was increased in LDLr-/- and APO1-/- (12.1±0.7 and 12.8±0.8) compared to WT (9.4±1.1 pA/pF) resulting in altered calcium handling in LDLr-/- and APO1-/- vs WT mice (increased calcium transient and fractional SR calcium release) and prolongation of AP and QTc duration (APD90 102±4 and 106±3 vs 84.4±3.1 and QTc 50.9±1.3 and 52.3 vs 43.8±1.18 ms, respectively.In LDLr-/- and APO1-/- hearts 1.7 and 1.3% of the attempts to induce arrhythmias resulted in VT/VF compared to 6.9% in WT. There was no significant difference in the induction of premature beats although (12.8% in WT vs 15.5 and 15.8 in LDL-/- and APO-/-). The AAR was not significantly different in LDLr -/-, APO1-/- and WT mice.Conclusion:Hypercholesterolemia protects against the occurrence of re-entrant arrhythmias during myocardial ischemia due to AP prolongation caused by an increase of the L-type calcium current.

Acute kidney injury due to rhabdomyolysis after status epilepticus: Two pediatric case reports

Rhabdomyolysis is defined as degeneration of skeletal muscle due to traumatic or non-traumatic causes. With the injury of sarcolemma, myocyte contents (myoglobin, enzymes and electrolytes) leakage into the plasma and urine occurs. If rhabdomyolysis is not recognized and untreated, severe even fatal complications such as acute kidney injury (AKI), hypocalcemia, hyperkalemia, hypovolemia, muscle necrosis, cardiac arrythmias and compartment syndrome may occur. Status epilepticus is an uncommon cause of rhabdomyolysis and myoglobinuria. We report here two pediatric patients, who developed myoglobinuria and AKI due to status epilepticus.

Enhanced Ca2+ Influx through Cardiac L-Type Ca2+ Channels Maintains the Systolic Ca2+ Transient in Cardiac Unloading

Purpose The Ca2+ transient couples excitation and contraction in cardiac myocytes. Its magnitude is determined by both, sarcolemmal Ca2+ influx and Ca2+ release from the sarcoplasmic reticulum (SR). Alteration of the Ca2+ transient can cause contractile failure and ventricular arrhythmias. The effect of cardiac atrophy on the cardiac Ca2+ transient and its underlying mechanisms is unknown. Methods and Materials To induce cardiac atrophy we unloaded left ventricles of male Lewis rats for two weeks using heterotopic heart transplantation. The SR Ca2+ content was determined by caffeine induced Ca2+ release. Results The SR Ca2+ content in myocytes isolated from atrophic hearts was ~50% lower than in control myocytes. Similarly, diastolic spark frequency was reduced by ~80% in atrophic cardiac myocytes. Surprisingly, however, systolic Ca2+ transients remained unaffected in spite of the reduced SR Ca2+ content and SR Ca2+ release. Action potential clamping demonstrated a marked prolongation of action potentials in endocardial (~+50%) and epicardial myocytes (~+250%) of atrophic hearts which was associated with a ~2- to 4-fold increased action potential driven sarcolemmal Ca2+ influx. Conclusions These results show that cardiac atrophy causes a large reduction of myocyte SR Ca2+ content. Nevertheless, the systolic Ca2+ transient is maintained by an enhanced sarcolemmal Ca2+ influx which compensates for the reduced Ca2+ release from the unloaded SR.