Heart Work Research Articles

Length Dependence of Force Generation is Controlled by Phosphorylation of cTnI at Serines 23/24

The steepness of the Frank-Starling relationship is modulated by numerous physiological factors including beta-adrenergic stimulation, which steepens the relationship. This arises in part from increased myofibrillar length dependence of force and power by PKA, a downstream signaling molecule of the beta-adrenergic system. Since PKA has multiple myofibrillar substrates including titin, myosin binding protein-C (MyBP-C), and cardiac troponin I (cTnI), we sought to define if phosphorylation of one of these molecules was sufficient to control length-tension relationships. We focused on cTnI since (i) we previously observed a relationship between cTnI phosphorylation and the steepness of ventricular function curves in rat working hearts, (ii) 2D-DIGE indicated a distribution of cTnI phosphorylation states consistent with our previous observation of two populations of length-tension relationships (one shallow the other steep) in rat skinned cardiac myocytes, and (iii) troponin can be more readily exchanged in permeabilized striated muscle cell preparations. To test if PKA-mediated phosphorylation of cTnI is sufficient to mediate length dependence of force we used skinned rat slow-twitch skeletal muscle fibers, which exhibit shallow length-tension relationships that are unaltered by PKA. A sarcomere length-tension relationship was measured during submaximal Ca2+ activation, then the fiber was incubated in a troponin (Tn) exchange solution, which replaced ∼80% of the endogenous slow-skeletal Tn with cTn. After cTn incorporation the length-tension relationship remained shallow as predicted since the purified cTnI lacks phosphate incorporation. Next, the fiber was incubated in PKA, which caused the length-tension relationship to shift from shallow to steep. In addition, exchange with cTn having cTnI serines 23/24 modified to aspartic acids to mimic phosphorylation steepened the length-tension relationship. These results indicate that phosphorylation of cTnI serines 23/24 is sufficient to control length dependence of force generation in striated muscle.

Additive Compensatory Effects of Cardiac Troponin I and Cardiac Troponin T N-Terminal Truncations on the Disease Phenotypes of a Familial Hypertrophic Cardiomyopathy Mutation (E180G) of α-Tropomyosin

A naturally occurring proteolytic N-terminal truncation of cardiac troponin I (cTnI-ND) has been shown to compensate for functional abnormalities caused by cardiomyopathic mutations. A proteolytic N-terminal truncation of cardiac TnT (cTnT-ND) elongates ventricular ejection time to compensate for cardiac output against high pressure load. To investigate the mechanisms for these troponin modifications to modulate the function of cardiac muscle thin filament, we produced transgenic mouse lines co-expressing cTnI-ND and/or cTnT-ND with a family hypertrophic cardiomyopathy mutation of cardiac α-tropomyosin (TM-E180G). The over expression of TM-E180G resulted in ∼90% replacement of endogenous α-tropomyosin in the cardiac muscle with normal total stoichiometry. Functional studies in ex vivo working hearts of 2-month-old TM-E180G mice showed lower diastolic velocity and higher left ventricular diastolic pressure, indicating higher Ca2+ sensitivity. β-MHC expression together with myocardial fibrosis was found in the left ventricle of 28-day and 2-month-old TM-E180G mice with early failing phenotypes (lower stroke volume and lower systolic velocity). In double and triple transgenic mouse hearts, expression of cTnI-ND and/or cTnT-ND decreased the occurrence of β-MHC in TM-E180G mouse hearts. Functional studies showed cTnI-ND+cTnT-ND did not override the contractile phenotype of TM E180G mutation but had beneficial effects on improving stroke volume and reducing fibrosis, with additive effects in the triple transgenic hearts. While TM-E180G mice usually die between 4 and 5 months of age, cardiac function of TM-E180G+cTnI-ND+cTnT-ND triple transgenic mice remained apparently normal at 10-11 months of age as shown by the compensated heart function and cardiac efficiency with minimal β-MHC occurrence. These results demonstrated compensatory effects of posttranslational modifications of troponin on the functional abnormality of tropomyosin for potential applications in the treatment of heart failure.

Prying open the space for social work in the new millennium

Social work in the United Kingdom faces all manner of woes. Critical public inquiries, disgruntled users of the service, the bureaucratisation of practice, problems with recruitment, and the overhaul of training, all continue to reinforce a culture of pessimism. It has been suggested that social work in the United Kingdom stands at the crossroads where a decision must be made either to accept these depressing conditions as they are, or to challenge them by asserting a new future for a reinvigorated profession. The latter option is supported by the authors of this article because we share the view that as social workers we have available to us discursive freedom with which to analyse the profession’s contemporary ailments and to find a way through them based on a discourse of social justice. The idea and practice of discursive freedom can be captured in the heuristic notion of ‘space’ which the authors use here as a shared focus for analysing contemporary social work from four different critical perspectives. In this way a dialogue is promoted between theory and practice and within critical theory. In its method and its results this inquiry is still very much work-in-progress. This provisional quality sits comfortably with the notion of ‘space’ and gives rein to its recursive qualities. These qualities, it is argued, must lie at the heart of transformative social work.

Pressure-overload-induced heart failure induces a selective reduction in glucose oxidation at physiological afterload

Development of heart failure is known to be associated with changes in energy substrate metabolism. Information on the changes in energy substrate metabolism that occur in heart failure is limited and results vary depending on the methods employed. Our aim is to characterize the changes in energy substrate metabolism associated with pressure overload and ischaemia-reperfusion (I/R) injury. We used transverse aortic constriction (TAC) in mice to induce pressure overload-induced heart failure. Metabolic rates were measured in isolated working hearts perfused at physiological afterload (80 mmHg) using (3)H- or (14)C-labelled substrates. As a result of pressure-overload injury, murine hearts exhibited: (i) hypertrophy, systolic, and diastolic dysfunctions; (ii) reduction in LV work, (iii) reduced rates of glucose and lactate oxidations, with no change in glycolysis or fatty acid oxidation and a small decrease in triacylglycerol oxidation, and (iv) increased phosphorylation of AMPK and a reduction in malonyl-CoA levels. Sham hearts produced more acetyl CoA from carbohydrates than from fats, whereas TAC hearts showed a reverse trend. I/R in sham group produced a metabolic switch analogous to the TAC-induced shift to fatty acid oxidation, whereas I/R in TAC hearts greatly exacerbated the existing imbalance, and was associated with a poorer recovery during reperfusion. Pressure overload-induced heart failure and I/R shift the preference of substrate oxidation from glucose and lactate to fatty acid due to a selective reduction in carbohydrate oxidation. Normalizing the balance between metabolic substrate utilization may alleviate pressure-overload-induced heart failure and ischaemia.

FOXO1-mediated upregulation of pyruvate dehydrogenase kinase-4 (PDK4) decreases glucose oxidation and impairs right ventricular function in pulmonary hypertension: therapeutic benefits of dichloroacetate

Pyruvate dehydrogenase kinase (PDK) is activated in right ventricular hypertrophy (RVH), causing an increase in glycolysis relative to glucose oxidation that impairs right ventricular function. The stimulus for PDK upregulation, its isoform specificity, and the long-term effects of PDK inhibition are unknown. We hypothesize that FOXO1-mediated PDK4 upregulation causes bioenergetic impairment and RV dysfunction, which can be reversed by dichloroacetate. Adult male Fawn-Hooded rats (FHR) with pulmonary arterial hypertension (PAH) and right ventricular hypertrophy (RVH; age 6-12 months) were compared to age-matched controls. Glucose oxidation (GO) and fatty acid oxidation (FAO) were measured at baseline and after acute dichloroacetate (1 mM × 40 min) in isolated working hearts and in freshly dispersed RV myocytes. The effects of chronic dichloroacetate (0.75 g/L drinking water for 6 months) on cardiac output (CO) and exercise capacity were measured in vivo. Expression of PDK4 and its regulatory transcription factor, FOXO1, were also measured in FHR and RV specimens from PAH patients (n = 10). Microarray analysis of 168 genes related to glucose or FA metabolism showed >4-fold upregulation of PDK4, aldolase B, and acyl-coenzyme A oxidase. FOXO1 was increased in FHR RV, whereas HIF-1 α was unaltered. PDK4 expression was increased, and the inactivated form of FOXO1 decreased in human PAH RV (P < 0.01). Pyruvate dehydrogenase (PDH) inhibition in RVH increased proton production and reduced GO's contribution to the tricarboxylic acid (TCA) cycle. Acutely, dichloroacetate reduced RV proton production and increased GO's contribution (relative to FAO) to the TCA cycle and ATP production in FHR (P < 0.01). Chronically dichloroacetate decreased PDK4 and FOXO1, thereby activating PDH and increasing GO in FHR. These metabolic changes increased CO (84 ± 14 vs. 69 ± 14 ml/min, P < 0.05) and treadmill-walking distance (239 ± 20 vs. 171 ± 22 m, P < 0.05). Chronic dichloroacetate inhibits FOXO1-induced PDK4 upregulation and restores GO, leading to improved bioenergetics and RV function in RVH.

Rehabilitative exercise in a rat model of doxorubicin cardiotoxicity

The use of exercise to minimize doxorubicin (DOX)-induced cardiotoxicity is gaining attention. However, very few clinically relevant reports exist investigating the effects of exercise performed during and following DOX treatments. The purpose of this study, therefore, was to examine the effects of voluntary wheel running during and following DOX treatment using two models of late-onset DOX cardiotoxicity in the rat. Female Sprague-Dawley rats received either DOX or saline injections using one of two separate treatment regimens. These regimens involved either daily or weekly DOX injections with cumulative doses for both protocols totaling 15 mg/kg. Daily DOX injections were 1 mg/kg and lasted for 15 consecutive days while weekly DOX injections were 2.5 mg/kg and lasted for six consecutive weeks with control animals receiving matched saline injection regimens. Immediately following the initial DOX/saline injection, animals were randomly housed in cages with voluntary running wheels or standard rat cages throughout DOX/saline treatments and continued until reaching 10 weeks. Cardiac function was then assessed using echocardiography and an isolated working heart model, and myosin heavy chain (MHC) isoform distribution was assessed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. When compared wth controls, daily DOX treatment resulted in reduced running wheel distances at weeks 2-10 (P < 0.05), and weekly DOX treatment resulted in reduced running wheel distances at weeks 2, 6 and 10 (P < 0.05). Nonetheless, wheel running during and following daily and weekly DOX dosing protected against DOX-induced cardiotoxicity by preserving maximal mitral and aortic blood flow velocities, left ventricular developed pressure and MHC isoform expression. In conclusion, the overall reduced volume of activity during and following daily and weekly DOX treatments attenuated DOX-induced cardiac dysfunction suggesting that low-volume endurance training may be an effective rehabilitative approach in minimizing DOX cardiotoxicity in cancer patients.

QnAs with Benjamin D. Santer

When Benjamin Santer began studying the Earth’s climate in the late 1970s, he simply wanted to understand the links between human behavior and global climate change. Computer models and statistical analysis enabled him to measure this relationship. By developing “fingerprints” that distinguish between human and natural influences on climate, Santer, a recently elected member of the National Academy of Sciences and atmospheric scientist at the Lawrence Livermore National Laboratory in Livermore, California, became one of the first scientists to prove the existence of human-induced climate change. Many groups have since independently confirmed those findings. Santer’s work has put him at the heart of the political debate surrounding anthropogenic climate change. The fight, at times, has turned vicious: in 1996, the Global Climate Coalition accused him of “scientific cleansing,” a spiteful claim, he says, given the ethnic cleansing going on in Bosnia at that time. Undeterred, Santer continued his “fingerprint” research and received two awards for this work in 1998: the prestigious MacArthur Fellowship and the Norbert Gerbier–MUMM International Award from the World Meteorological Organization, given annually to the researcher with the year’s best climate science study. Here, Santer discusses how his research helps shift discussions of climate change from ideology to science. Benjamin D. Santer. > PNAS:The heart of your work relies on a method known as fingerprinting. Can you describe …

UCP3 Regulates Cardiac Efficiency and Mitochondrial Coupling in High Fat–Fed Mice but Not in Leptin-Deficient Mice

These studies investigate the role of uncoupling protein 3 (UCP3) in cardiac energy metabolism, cardiac O2 consumption (MVO2), cardiac efficiency (CE), and mitochondrial uncoupling in high fat (HF)–fed or leptin-deficient mice. UCP3KO and wild-type (WT) mice were fed normal chow or HF diets for 10 weeks. Substrate utilization rates, MVO2, CE, and mitochondrial uncoupling were measured in perfused working hearts and saponin-permeabilized cardiac fibers, respectively. Similar analyses were performed in hearts of ob/ob mice lacking UCP3 (U3OB mice). HF increased cardiac UCP3 protein. However, fatty acid (FA) oxidation rates were similarly increased by HF diet in WT and UCP3KO mice. By contrast, MVO2 increased in WT, but not in UCP3KO with HF, leading to increased CE in UCP3KO mice. Consistent with increased CE, mitochondrial coupling was increased in the hearts of HF-fed UCP3KO mice. Unexpectedly, UCP3 deletion in ob/ob mice reduced FA oxidation but had no effect on MVO2 or CE. In addition, FA-induced mitochondrial uncoupling was similarly enhanced in U3OB compared with ob/ob hearts and was associated with elevated mitochondrial thioesterase-1 protein content. These studies show that although UCP3 may mediate mitochondrial uncoupling and reduced CE after HF feeding, it does not mediate uncoupling in leptin-deficient states.

Anita Ilta Garey and Karen V. Hansen (Eds.). At the Heart of Work and Family: Engaging the Ideas of Arlie Hochschild. Foreword by Barabara Ehrenreich. New Brunswick, New Jersy, and London: Rutgers University Press

"Anita Ilta Garey and Karen V. Hansen (Eds.). At the Heart of Work and Family: Engaging the Ideas of Arlie Hochschild. Foreword by Barabara Ehrenreich. New Brunswick, New Jersy, and London: Rutgers University Press." Journal of Comparative Family Studies, 43(6), pp. 943–944

Effects of temperature on the nitric oxide-dependent modulation of the Frank–Starling mechanism: the fish heart as a case study

The Frank–Starling law is a fundamental property of the vertebrate myocardium which allows, when the end-diastolic volume increases, that the consequent stretch of the myocardial fibers generates a more forceful contraction. It has been shown that in the eel (Anguilla anguilla) heart, nitric oxide (NO) exerts a direct myocardial relaxant effect, increasing the sensitivity of the Frank–Starling response (Garofalo et al., 2009). With the use of isolated working heart preparations, this study investigated the relationship between NO modulation of Frank–Starling response and temperature challenges in the eel. The results showed that while, in long-term acclimated fish (spring animals perfused at 20°C and winter animals perfused at 10°C) the inhibition of NO production by L-N5 (1-iminoethyl)ornithine (L-NIO) significantly reduced the Frank–Starling response, under thermal shock conditions (spring animals perfused at 10 or 15°C and winter animals perfused at 15 or 20°C) L-NIO treatment resulted without effect. Western blotting analysis revealed a decrease of peNOS and pAkt expressions in samples subjected to thermal shock. Moreover, an increase in Hsp90 protein levels was observed under heat thermal stress. Together, these data suggest that the NO synthase/NO-dependent modulation of the Frank–Starling mechanism in fish is sensitive to thermal stress.

Hearts from Donations after Circulatory Death (DCD) Donors - Ischaemic Post-Conditioning Significantly Improves Recovery of Cardiac Function Following Warm Ischaemia in A Porcine Model

Introduction: Utilisation of hearts from Donations after circulatory death (DCD) donors has been limited by fear of warm ischaemic damage. We aim to investigate the impact of varying periods of warm ischaemia on cardiac function in DCD hearts, and evaluate ischaemic post-conditioning strategies to limit warm ischaemic injury. Methods: Utilising a porcine DCD model, 3 warm ischaemic time (WIT) periods were evaluated. All hearts were antegrade flushed with Celsior solution after the designated period of warm ischaemia. Ischaemic post-conditioning was affected with the supplementation of Celsior with glyceryl trinitrate (GTN), erythropoietin (EPO), and zoniporide - this approach has been studied extensively in our laboratory1. (table 1)Hearts were explanted onto an isolated working heart circuit. Left heart performance was assessed for 4 hours - functional assessment (Cardiac Output, Coronary Flow, Left Atrial Pressure (LAP) vs Aortic Flow (AF) challenge), metabolic recovery (pH, lactate, myocardial oxygen consumption), and biochemical parameters (troponin, LDH) were evaluated. Results: When compared with control hearts, Group 1 hearts showed complete functional recovery, Group 2 had partial recovery and Group 3 had no recovery. Cardiac Output was inferior with Group 2 hearts (graph 1). The increase in AF in response to increased LAP was significantly blunted for Group 2 (p=0.05), when compared with control and Group 1. Group 2 hearts also remained more acidotic (p=0.03), had higher lactate levels (p=0.03), greater troponin release (p=0.03) and had non-significant trends towards higher LDH levels than control or Group 1 hearts. Following the supplementation of the preservation flush for 30 minute warm ischaemia hearts (Group 4) there was a significantly improved functional and biochemical recovery when compared with group 2 hearts (unsupplemented 30 minute warm ischaemia hearts). Comparing group 2 and group 4, group 4 had superior Cardiac Output (p < 0.01, see graph 1), higher coronary flows (p < 0.01), superior performance in the AF vs LAP challenge (p = 0.03), and decreased troponin release (p=0.05).Figure: [Graph 1]Conclusion: Hearts with a WIT of less than 20 minutes demonstrate excellent recovery, supporting the potential for DCD hearts in transplantation. The detrimental effects of warm ischaemia become evident beyond 20 minutes - here, ischaemc post-conditioning strategies aimed at mitigating ischaemia-reperfusion injury significantly improve cardiac recovery. With the utilization of such strategies in preserving cardiac function following 30 minutes of warm ischaemia, the potential for translation to clinical DCD heart transplantation is greatly strengthened and warrants further investigation.

Stabilizing endothelium of donor hearts with fusogenic liposomes reduces myocardial injury and dysfunction

BackgroundMyocardial injury after heart transplantation is a consequence of pathophysiologic events initiated by local ischemia/reperfusion injury that is further aggravated by the inflammatory response due to blood exposure to the pump’s artificial surfaces during cardiopulmonary bypass. The purpose of the present study was to determine the effectiveness of fusogenic lipid vesicles (FLVs) in enhancing the cardioprotective effect of St. Thomas organ preservation solution (ST). We hypothesized that donor hearts preserved with ST+FLVs will stabilize the endothelium during reperfusion, which, in turn, will reduce both endothelial barrier dysfunction and myocardial damage. MethodsTo examine the effect of ST+FLVs therapy in vitro, C3b deposition and adhesion molecule expression studies were performed on human umbilical vein endothelial cells challenged with plastic contact-activated plasma. To assess the therapy in vivo, a cervical heterotopic working heart transplantation model in rats was used. Donor hearts were preserved for 1 h at 27°C (15 min) and 4°C (45 min) and, after transplantation, were followed up for 2 h. Left ventricular function and the blood cardiac troponin I levels were quantified. ResultsHuman umbilical vein endothelial cells treated with ST+FLVs had reduced C3b deposition and expression of adhesion molecules compared with ST alone (P < 0.05). Donor hearts receiving ST+FLVs therapy had reduced left ventricular dysfunction and cardiac troponin I compared with ST alone. ConclusionsWe concluded that FLVs enhanced the cardioprotective effect of ST and reduced postischemic left ventricular dysfunction and myocardial damage. The mechanism of protection appears to be associated with the stabilization of endothelial cell membranes owing to incorporation of FLV-derived lipids.

Review of "Selling Out: Academic Freedom and the Corporate Academy"

Woodhouse, Howard (2009). Selling Out: Academic and Corporate Academy. Montreal & Kingston: McGill-Queen's University Press. Pages: 360. Price: 35.95 CAD (cloth).Dr. Howard Woodhouse (College of Education, University of Saskatchewan) begins book by disclosing his own firing from University of Western Ontario close thirty years ago. This extreme disciplinary action took root when without protection of tenure or freedom, he authored a letter that was published in university newspaper in which he criticized a peer's position on South Africa apartheid and it culminated when he penned a report about the future plans of educational development office(p.3). Woodhouse sued for wrongful dismissal and ultimately Ontario Human Rights Commission found on his side of dispute. This author has both direct personal and professional experience with an freedom case and has published in this area for several decades. This considerable vantage point might be, in part, what prompted him frame his cumulative argument in a series of case studies of people have opposed influence of on teaching and research at Canadian universities (p.3) that serve examine both personal and institutional levels. He also takes care situate concrete narratives alongside abstract theory with key attention paid the concept of 'generalization' operant in wok of Alfred North Whitehead (p.5). essence of ongoing argument is that traditional goal of university, provoke and share knowledge, is antithetical to, or in necessary conflict with (p.21), corporatist academy of 21 century which privileges demands over independent thought, research, teaching and learning. Woodhouse warns that current innovation, commercialization and federal government funding driven Canadian higher education engineers ready-made products and standardized ideas for corporate market (p.38) while simultaneously academic skills are decoupled from any disciplinary base (p.26).The structure of monograph is comprised of an introduction, seven chapters supported by approximately 70 pages of notes, and a short back of book index. heart of work is engaging set of case studies which vary from iconic Nancy Olivieri affair (Chapter 3: Taking on Big Pharma) lesser known set of circumstances of other scholars who spoke out against forces in Canadian higher education. These stories of resistance are complemented by broader narratives, including The Market Model of Education and Threat Academic Freedom and The Value Program in Theory in Practice. Through two closing chapters, which counter ubiquitous model of student evaluation as customer satisfaction and examine People's Free University of Saskatchewan, book ultimately pushes questions that many of us in academe grapple with today. To what extent is resistance in form of a civil commons (p.261) a possibility? How much daring will it take and at what personal and professional cost, for example to be shunned, persecuted and possibly dismissed (p.11)?Selling Out is highly relevant contemporary Canadian higher education, including its current dramas, such as August 2011 agreement between York University and RIM co-founder Jim Balsillie's private think tank, Centre for International Governance Innovation (CIGI) in which the University agrees that it will allow CIGI not only a voice in who should be hired in program at York, but veto power over whom University can consider for hiring. …

Left ventricular output and aortic blood flow in response to changes in preload and afterload in the preterm piglet heart

Low systemic blood flow occurs in up to 30% of infants born at less than 30 wk gestation. It is associated with increased morbidity and mortality, and current treatments are ineffective in 40% of cases. The aim of this study was to assess the ability of the preterm heart to respond to the acute shifts in preload and afterload that occur at the time of birth. Myocardial and coronary vascular function was assessed using an isolated working heart model in term (115 days) and preterm (92 days) piglets. Cardiac output/kg body wt in preterm hearts was ∼50% lower than that of term hearts (P = 0.001). Pressure development was similar in term and preterm hearts. Elevations in preload increased cardiac output and aortic flow similarly in term and preterm hearts, demonstrating significant preload "reserve". By contrast, elevations in afterload markedly depressed aortic flow, with a greater proportion of cardiac output being distributed to coronary flow in preterm hearts at high afterloads. The demands of increased workload were associated with greater increases in coronary flow in preterm hearts compared with term hearts. In preterm hearts, exposure to maternal glucocorticoids resulted in increased aortic flow when afterload was below 25 mmHg. These data suggest the preterm heart lacks the functional capacity to acutely adapt to postnatal afterload. To maximize systemic blood flow in preterm infants, treatments limiting afterload, while harnessing significant preload reserve, should be further explored.

Abstract 11: Transgenic Overexpression of Snf1-Related Kinase in the Heart Improves Cardiac Metabolic Efficiency and Response to Myocardial Ischemia

Introduction: Snf1-related Kinase (SNRK) is a serine/threonine kinase with sequence similarity to AMP-activated kinase. The function and substrates of SNRK are unknown. We have found that SNRK is upregulated in hearts from patients with ischemic cardiomyopathy, and our previous gene array data suggested that SNRK alters metabolic gene expression. Here, we assessed the hypothesis that SNRK regulates cardiac metabolism. Results: SNRK transgenic mice with specific overexpression of SNRK in the heart displayed decreased glycolysis (1267.66 vs. 1925.60 nmol/min/g dhw, p=0.004, n=6), glucose oxidation (441.73 vs. 602.68 nmol/min/g dhw, p=0.068, n=6), and palmitate oxidation (262.39 vs. 385.07 nmol/min/g dhw, p=0.005, n=6) compared to wild type littermate controls in perfused working hearts. However, cardiac power output and function were maintained, demonstrating that SNRK transgenic mice have increased metabolic efficiency. Mitochondria isolated from SNRK transgenic mice had increased state 3 respiration and oxidative capacity, along with an increased respiratory control ratio (state 3/state 4 respiration), indicating reduced mitochondrial uncoupling. To identify the mechanism for the effects of SNRK on metabolic flux, we performed a yeast two hybrid screen with SNRK bait. Tribbles homolog 3 (Trb3), an inhibitor of Akt, was identified as a SNRK-interacting protein, which was verified by co-immunoprecipitation and mammalian two hybrid assay. Trb3 protein levels were increased in the SNRK transgenic mice, and phosphorylation of Akt and its substrate GSK3 was reduced. SNRK transgenic mice also had decreased mRNA levels of glucose transporter 1 and 4, hexokinase II, and phosphofructokinase. Additionally, mRNA levels of the fatty acid metabolism regulators peroxisome proliferator-activated receptor (PPAR) α and PPARγ were reduced, as well as their targets uncoupling protein 2 and 3. Finally, SNRK transgenic mice had decreased infarct size compared to wild type littermates (14.35% vs. 20.63% total left ventricle area, p=0.023, n=6) following myocardial infarction for seven days. Conclusions: Our results demonstrate that SNRK increases cardiac metabolic and mitochondrial efficiency and resistance to myocardial infarct cell death.

Physiological changes in cycle rickshaw pullers after strenuous exercise

Background: Cycle Rickshaw is a human-powered transportation device. A large number of people remain engaged in the occupation of pulling cycle rickshaw. Objectives: The objectives of the study were to assess nutritional status of the cycle rickshaw pullers and their workload by working heart rate and energy expenditure. Methods and Materials: Eighteen rickshaw pullers and eleven control subjects were selected after clinical examination. Subjects were asked to pull the rickshaw in two phases - phase 1 (before lunch) and phase 2 (after lunch) each of 3 cycles of 15 min duration each followed by 15 min rest with two passengers. Heart rate was recorded continuously using a heart rate monitor. Average working heart rate (AWHR), peak working heart rate (PWHR) and energy expenditure (EE) were calculated. Maximal heart rate (HRmax) was also recorded in the laboratory. The control subjects were allowed to work in a cycle ergometer in the laboratory. Results: There was no significant difference between the mean values of rickshaw pullers and those of control subjects in relation to age, BMI, fat% and HRmax (beats/min). The AWHR, PWHR and EE values of rickshaw pullers showed the workload as ‘heavy’ to ‘very heavy’ category. Conclusion: The result of the study will be beneficial for cycle rickshaw pullers, health administrators and manufacturers of cycle rickshaw.DOI: http://dx.doi.org/10.3126/ijosh.v2i2.6567 International Journal of Occupational Safety and Health, Vol 2. No 2 (2012) 23-26

Assessment of cardiac strain in small - scale aluminium casting works.

Background: The occupational health status scenario in unorganised sector is not impressive. There is a lack of awareness on occupational health and safety issues and manual labour is still obligatory. Ergonomic and work physiological studies conducted among different unorganised sector occupations are scanty. Aims and Objective: The present study intended a physiological evaluation of workload in small scale aluminium casting works. In accordance, cardiac strain of the workers is assessed in actual work situation. Methods: Seventeen regular male workers (mean age 32.6 ± 10.9; range 22 – 55) years, were examined for the magnitude of physiological strain. Different tasks performed were identified including work and rest hours. Working heart rate, net cardiac cost, relative cardiac cost and recovery heart rates were determined. Tasks performed were analysed in terms of heaviness, recommended strain level and thermal stress of the workplace. Results: Work study revealed the predominant static nature of the tasks performed. Overall strain of the job appeared to be moderate in nature with mean working heart rate of 99 ± 5.2 beats/min. Recovery patterns were inadequate for majority of the workers. Thermal stress prevailing was more than the recommended level. Conclusion: The subjects were exposed to cumulative circulatory stress which might have deleterious long term effect particularly on older workers. Interventions are required to ameliorate ergonomic stressors, which indicate further scope of study.DOI: http://dx.doi.org/10.3126/ijosh.v2i2.6565 International Journal of Occupational Safety and Health, Vol 2. No 2 (2012) 8-13

NADH Fluorescence Imaging of Isolated Biventricular Working Rabbit Hearts

Since its inception by Langendorff1, the isolated perfused heart remains a prominent tool for studying cardiac physiology2. However, it is not well-suited for studies of cardiac metabolism, which require the heart to perform work within the context of physiologic preload and afterload pressures. Neely introduced modifications to the Langendorff technique to establish appropriate left ventricular (LV) preload and afterload pressures3. The model is known as the isolated LV working heart model and has been used extensively to study LV performance and metabolism4-6. This model, however, does not provide a properly loaded right ventricle (RV). Demmy et al. first reported a biventricular model as a modification of the LV working heart model7, 8. They found that stroke volume, cardiac output, and pressure development improved in hearts converted from working LV mode to biventricular working mode8. A properly loaded RV also diminishes abnormal pressure gradients across the septum to improve septal function. Biventricular working hearts have been shown to maintain aortic output, pulmonary flow, mean aortic pressure, heart rate, and myocardial ATP levels for up to 3 hours8. When studying the metabolic effects of myocardial injury, such as ischemia, it is often necessary to identify the location of the affected tissue. This can be done by imaging the fluorescence of NADH (the reduced form of nicotinamide adenine dinucleotide)9-11, a coenzyme found in large quantities in the mitochondria. NADH fluorescence (fNADH) displays a near linearly inverse relationship with local oxygen concentration12 and provides a measure of mitochondrial redox state13. fNADH imaging during hypoxic and ischemic conditions has been used as a dye-free method to identify hypoxic regions14, 15 and to monitor the progression of hypoxic conditions over time10. The objective of the method is to monitor the mitochondrial redox state of biventricular working hearts during protocols that alter the rate of myocyte metabolism or induce hypoxia or create a combination of the two. Hearts from New Zealand white rabbits were connected to a biventricular working heart system (Hugo Sachs Elektronik) and perfused with modified Krebs-Henseleit solution16 at 37 °C. Aortic, LV, pulmonary artery, and left & right atrial pressures were recorded. Electrical activity was measured using a monophasic action potential electrode. To image fNADH, light from a mercury lamp was filtered (350±25 nm) and used to illuminate the epicardium. Emitted light was filtered (460±20 nm) and imaged using a CCD camera. Changes in the epicardial fNADH of biventricular working hearts during different pacing rates are presented. The combination of the heart model and fNADH imaging provides a new and valuable experimental tool for studying acute cardiac pathologies within the context of realistic physiological conditions.

NADH Fluorescence Imaging of Isolated Biventricular Working Rabbit Hearts

Since its inception by Langendorff1, the isolated perfused heart remains a prominent tool for studying cardiac physiology2. However, it is not well-suited for studies of cardiac metabolism, which require the heart to perform work within the context of physiologic preload and afterload pressures. Neely introduced modifications to the Langendorff technique to establish appropriate left ventricular (LV) preload and afterload pressures3. The model is known as the isolated LV working heart model and has been used extensively to study LV performance and metabolism4-6. This model, however, does not provide a properly loaded right ventricle (RV). Demmy et al. first reported a biventricular model as a modification of the LV working heart model7, 8. They found that stroke volume, cardiac output, and pressure development improved in hearts converted from working LV mode to biventricular working mode8. A properly loaded RV also diminishes abnormal pressure gradients across the septum to improve septal function. Biventricular working hearts have been shown to maintain aortic output, pulmonary flow, mean aortic pressure, heart rate, and myocardial ATP levels for up to 3 hours8.When studying the metabolic effects of myocardial injury, such as ischemia, it is often necessary to identify the location of the affected tissue. This can be done by imaging the fluorescence of NADH (the reduced form of nicotinamide adenine dinucleotide)9-11, a coenzyme found in large quantities in the mitochondria. NADH fluorescence (fNADH) displays a near linearly inverse relationship with local oxygen concentration12 and provides a measure of mitochondrial redox state13. fNADH imaging during hypoxic and ischemic conditions has been used as a dye-free method to identify hypoxic regions14, 15 and to monitor the progression of hypoxic conditions over time10.The objective of the method is to monitor the mitochondrial redox state of biventricular working hearts during protocols that alter the rate of myocyte metabolism or induce hypoxia or create a combination of the two. Hearts from New Zealand white rabbits were connected to a biventricular working heart system (Hugo Sachs Elektronik) and perfused with modified Krebs-Henseleit solution16 at 37 °C. Aortic, LV, pulmonary artery, and left & right atrial pressures were recorded. Electrical activity was measured using a monophasic action potential electrode. To image fNADH, light from a mercury lamp was filtered (350±25 nm) and used to illuminate the epicardium. Emitted light was filtered (460±20 nm) and imaged using a CCD camera. Changes in the epicardial fNADH of biventricular working hearts during different pacing rates are presented. The combination of the heart model and fNADH imaging provides a new and valuable experimental tool for studying acute cardiac pathologies within the context of realistic physiological conditions.

Heart rate reduction by If-inhibition improves vascular stiffness and left ventricular systolic and diastolic function in a mouse model of heart failure with preserved ejection fraction

In diabetes mellitus, heart failure with preserved ejection fraction (HFPEF) is a significant comorbidity. No therapy is available that improves cardiovascular outcomes. The aim of this study was to characterize myocardial function and ventricular-arterial coupling in a mouse model of diabetes and to analyse the effect of selective heart rate (HR) reduction by If-inhibition in this HFPEF-model. Control mice, diabetic mice (db/db), and db/db mice treated for 4 weeks with the If-inhibitor ivabradine (db/db-Iva) were compared. Aortic distensibility was measured by magnetic resonance imaging. Left ventricular (LV) pressure-volume analysis was performed in isolated working hearts, with biochemical and histological characterization of the cardiac and aortic phenotype. In db/db aortic stiffness and fibrosis were significantly enhanced compared with controls and were prevented by HR reduction in db/db-Iva. Left ventricular end-systolic elastance (Ees) was increased in db/db compared with controls (6.0 ± 1.3 vs. 3.4 ± 1.2 mmHg/µL, P < 0.01), whereas other contractility markers were reduced. Heart rate reduction in db/db-Iva lowered Ees (4.0 ± 1.1 mmHg/µL, P < 0.01), and improved the other contractility parameters. In db/db active relaxation was prolonged and end-diastolic capacitance was lower compared with controls (28 ± 3 vs. 48 ± 8 μL, P < 0.01). These parameters were ameliorated by HR reduction. Neither myocardial fibrosis nor hypertrophy were detected in db/db, whereas titin N2B expression was increased and phosphorylation of phospholamban was reduced both being prevented by HR reduction in db/db-Iva. In db/db, a model of HFPEF, selective HR reduction by If-inhibition improved vascular stiffness, LV contractility, and diastolic function. Therefore, If-inhibition might be a therapeutic concept for HFPEF, if confirmed in humans.