Hamster Heart Research Articles

Eplerenone inhibits the intracrine and extracellular actions of angiotensin II on the inward calcium current in the failing heart. On the presence of an intracrine renin angiotensin aldosterone system

The influence of chronic administration of eplerenone on the intracrine as well as on the extracellular action of angiotensin II (Ang II) on L-type inward calcium current was investigated in the failing heart of cardiomyopathic hamsters (TO-2).For this, eplerenone (200 mg/kg/day) was administered orally to 2 month-old cardiomyopathic hamsters for a period of 3 months. Measurements of the peak inward calcium current ( I Ca) was performed in single cells under voltage clamp using the whole cell configuration. The results indicated that eplerenone suppressed the intracrine action of Ang II (10 − 8 M) on peak I Ca density. Moreover, the intracellular dialysis of the peptide did not change the time course of I Ca inactivation in animals treated chronically with eplerenone. The extracellular administration of Ang II (10 − 8 M) incremented the peak I Ca density by only 20 ± 8% ( n = 30) compared with 38 ± 4% ( n = 35) ( P < 0.05) obtained in age-matched cardiomyopathic hamsters not exposed to eplerenone. Interestingly, the inhibitory of eplerenone (10 − 7 M) on the intracrine action of Ang II was also found, in vitro, but required an incubation period of, at least, 24 h. The inhibitory action of eplerenone on the intracellular action of Ang II was partially reversed by exposing the eplerenone-treated cells to aldosterone (10 nM) for a period of 24 h what supports the view that: a) the mineralocorticoid receptor(MR) was involved in the modulation of the intracrine action of the peptide; b) the effect of eplerenone on the intracrine as well as on the extracellular action of Ang II was related ,in part, to a decreased expression of membrane-bound and intracellular AT1 receptors. In conclusion: a) eplerenone inhibits the intracrine action of Ang II on inward calcium current and reduces drastically the effect of extracellular Ang II on I Ca; b) aldosterone is able to revert the effect of eplerenone; c) the mineralocorticoid receptor is an essential component of the intracrine renin angiotensin aldosterone system.

Late CD8+ T Cell-Dependent Xenoantibody Production in Innate Tolerant Nude Rats After Hamster Islet Grafting But Not After Hamster Heart Grafting

Xenograft rejection can be provoked by both the innate and adaptive immune compartments and close reciprocal interactions exist between these two systems. We investigated the interdependent roles of T and B lymphocytes in vascularized (heart) and cellular (islet) xenograft rejection in a model with established xeno-nonreactivity of the innate immune system. Specific innate xenotolerance was induced in nude rats bearing either a hamster heart or a hamster pancreatic islet graft by a tolerizing regimen consisting of donor antigen infusion, temporary natural killer cell depletion and a 4-week administration of leflunomide. One month after transplantation, syngeneic CD4 and CD8 T cells were adoptively transferred. Both vascular and cellular xenografts were rejected after CD4 T cell reconstitution, corresponding with production of high IgM and IgG xenoantibody titers. Deposition of xenoantibodies and complement was seen in the heart but not in the islet xenografts. After infusion of CD8 T cells, xenohearts underwent a delayed type of rejection without xenoantibody production and xenoislets were not rejected. In xenoislet recipients, CD8 dependent B cells were not tolerized, resulting in the production of IgG xenoantibodies belonging to Th2-dependent isotypes, known not to cause graft rejection, and deposited at the graft implantation site. We conclude that distinct mechanisms of immune activation underlie xenogeneic reactions against vascular and cellular grafts.

336. Adeno-Associated Viral-Mediated Gene Delivery of Thymosin-beta4 Enhance Heart Function and Improve Survival in TO2 Hamster Heart Failure Model

336. Adeno-Associated Viral-Mediated Gene Delivery of Thymosin-beta4 Enhance Heart Function and Improve Survival in TO2 Hamster Heart Failure Model

Xanthine Oxidase Inhibition Improves Left Ventricular Dysfunction in Dilated Cardiomyopathic Hamsters

Background Oxidative stress is implicated in cardiac remodeling and failure. We tested whether xanthine oxidase (XO) inhibition could decrease myocardial oxidative stress and attenuate left ventricular (LV) remodeling and dysfunction in the TO-2 hamster model of dilated cardiomyopathy. Methods and Results TO-2 hamsters were randomized to treatment with the XO inhibitor, allopurinol, or vehicle from 6 to 12 weeks of age. F1B hamsters served as controls. TO-2 hamsters treated with vehicle progressively developed severe LV systolic dysfunction and dilation between 6 and 12 weeks. Marked cardiac fibrosis was apparent in these hamsters at 12 weeks in comparison with F1B controls. The ratio of reduced to oxidized glutathione (GSH/GSSG) was decreased and malondialdehyde levels were increased in the hearts of vehicle-treated TO-2 hamsters. Treatment with allopurinol from 6 to 12 weeks attenuated LV dysfunction and dilation as well as myocardial fibrosis and the upregulation of a fetal-type cardiac gene. Allopurinol also inhibited both the decrease in GSH/GSSG ratio and the increase in malondialdehyde levels in the heart. Conclusions These results indicate that chronic XO inhibition with allopurinol attenuates LV remodeling and dysfunction as well as myocardial oxidative stress in this model of heart failure. Allopurinol may prove beneficial for the treatment of heart failure.

The Role of Graft and Host Accommodation in a Hamster-to-Rat Cardiac Transplantation Model

We evaluated the importance and mechanism of graft and host accommodation in hamster-to-rat cardiac xenotransplantation models. To evaluate graft accommodation, accommodated hamster grafts (Group 2) were transplanted to naïve host rats treated with FK506, and compared with naïve hamster grafts (Group 1). To evaluate host accommodation, three groups were evaluated: naive hamster hearts were transplanted to naïve hosts treated with FK506 (Group 3: 0.5 mg/kg, Group 4: 1.0 mg/kg) and splenectomy, and compared with accommodating hosts (Group 5) with FK506 0.5 mg/kg and splenectomy. We examined graft survival, histopathology, antihamster antibodies and B-1 cells in blood. Graft survival in Group 2 (3.4+/-0.9 days) was not significantly different from that in Group 1 (2.8+/-0.4 days). Graft survival in Groups 4 and 5 (>30 days) was significantly prolonged compared with that in Group 3 (6.0+/-0.7 days). Histopathology of Groups 1-3 showed humoral rejection, whereas Groups 4 and 5 showed normal histology and expression of protective genes. In Groups 1-3, antihamster immunoglobulin (Ig) M and B-1 cells increased significantly compared to Groups 4 and 5, where IgM and B-1 cells remained low or were reduced. Host accommodation was more important than graft accommodation. Accommodating grafts expressing protective genes were rejected with an elevation of both IgM and B-1 cells. In accommodated hosts, both IgM and B-1 cells decreased, suggesting that B-1 cells may be responsible for the production of antihamster antibodies. These results suggest that sufficient suppression of B-1 cells, resulting in decreased titers of antihamster antibodies, may play an important role in host accommodation.

Altered expression of connexin43 contributes to the arrhythmogenic substrate during the development of heart failure in cardiomyopathic hamster

Heart failure is known to predispose to life-threatening ventricular tachyarrhythmias even before compromising the systemic circulation, but the underlying mechanism is not well understood. The aim of this study was to clarify the connexin43 (Cx43) gap junction remodeling and its potential role in the pathogenesis of arrhythmias during the development of heart failure. We investigated stage-dependent changes in Cx43 expression in UM-X7.1 cardiomyopathic hamster hearts and associated alterations in the electrophysiological properties using a high-resolution optical mapping system. UM-X7.1 hamsters developed left ventricular (LV) hypertrophy by ages 6 approximately 10 wk and showed a moderate reduction in LV contractility at age 20 wk. Appreciable interstitial fibrosis was recognized at these stages. LV mRNA and protein levels of Cx43 in UM-X7.1 were unaffected at age 10 wk but significantly reduced at 20 wk. The expression level of Ser255-phosphorylated Cx43 in UM-X7.1 at age 20 wk was significantly greater than that in control golden hamsters at the same age. In UM-X7.1 at age 10 wk, almost normal LV conduction was preserved, whereas the dispersion of action potential duration was significantly increased. UM-X7.1 at age 20 wk showed significant reduction of cardiac space constant, significant decrease in conduction velocity, marked distortion of activation fronts, and pronounced increase in action potential duration dispersion. Programmed stimulation resulted in sustained ventricular tachycardia or fibrillation in UM-X7.1. LV activation during polymorphic ventricular tachycardia was characterized by multiple phase singularities or wavebreaks. During the development of heart failure in the cardiomyopathic hamster, alterations of Cx43 expression and phosphorylation in concert with interstitial fibrosis may create serious arrhythmogenic substrate through an inhibition of cell-to-cell coupling.

Inhibition of the membrane attack complex of complement for induction of accommodation in the hamster‐to‐rat heart transplant model

To induce accommodation in the hamster-to-rat cardiac transplantation model, in addition to cyclosporin A (CSA) to inhibit T-cell-mediated graft rejection, cobra venom factor (CVF) is often used to prevent complement-mediated graft rejection. Although it is generally assumed that CVF makes accommodation possible because it inactivates the complement membrane attack complex (MAC), it is not known which complement components must be inactivated and whether complement activation products generated by CVF are also involved in the induction of accommodation. Therefore, to investigate mechanisms by which CVF contributes to accommodation, we studied induction of accommodation of hamster hearts grafted into rats with complement deficiencies of C6; these rats cannot assemble the MAC but, in contrast to CVF, retain in their native state all complement proteins that precede the MAC. Golden Syrian hamster hearts were transplanted heterotopically into the abdomen of normocomplementemic and C6-deficient (C6D) PVG rats. Graft rejection was determined by cessation of palpable cardiac contractions. CSA, 10 mg/kg, was administered daily to all rats. Graft survival was compared in rats given CVF (60 U/kg 1-day pre-transplant and 20 U/kg/day for the next 9 days), C6D rats given no CVF, normocomplementemic rats given anti-C6 IgG or non-immune IgG but no CVF, and C6D rats reconstituted with normocomplementemic rat serum. Total complement and C6 serum levels were measured using hemolytic assays in rat peripheral blood. We found that hamster hearts transplanted into C6D rats receiving CSA but no CVF survived long-term, with histology typical of an accommodated heart. The accommodated hamster heart did not reconstitute C6 levels of the C6D recipient rats. Moreover, in normocomplementemic rats given anti-C6 antibodies (abs) to induce partial C6 deficiency, accommodation also developed without administration of CVF. Accommodation of the hamster heart failed to develop in C6D rats whose complement was reconstituted by administration of normocomplementemic rat serum given before and following transplantation. These studies demonstrate that, in this model, inhibition of MAC-mediated graft rejection is sufficient to allow the development of accommodation. Inactivation of C3 or other complement proteins of the alternate pathway, or the presence of complement-derived biologically active fragments, is not needed for development of accommodation.

Progression of Heart Failure Was Suppressed by Inhibition of Apoptosis Signal-Regulating Kinase 1 Via Transcoronary Gene Transfer

We examined whether the inhibition of apoptosis signal-regulating kinase 1 (ASK1) would attenuate the progression of heart failure in TO-2 hamsters with hereditary dilated cardiomyopathy. Heart failure remains the leading cause of mortality and requires novel therapies targeting the biologically relevant processes within cardiomyocytes that lead to cell death. Apoptosis signal-regulating kinase 1 is a key signaling molecule for cardiomyocyte death. We generated recombinant adeno-associated virus (rAAV) expressing an N-terminal truncated form of the dominant-negative mutant of ASK1 (ASKdeltaN(KR)). TO-2 hamsters were subjected to an in vivo rAAV transcoronary transfer. ASKdeltaN(KR) retained its dominant-negative activity in vitro. The rAAV expressing ASKdeltaN(KR) treatment inhibited ASK1 activation in the hamster hearts and suppressed progression of ventricular remodeling such as chamber dilation, impairment of contractile and relaxation functions, and fibrosis. Inhibition of ASK1 reduced the number of apoptotic cells and selectively attenuated c-Jun NH2-terminal kinase activation. Although the deficiency of delta-sarcoglycan, a genetic defect in the hamster, leads to the degradation of dystrophin, the treatment significantly protected hearts from this degradation, probably by inhibiting calpain activation. Apoptosis signal-regulating kinase 1 is involved in the pathogenesis of heart failure progression, mediated through c-Jun NH2-terminal kinase-mediated apoptosis and calpain-dependent dystrophin cleavage, and may be a therapeutic target to treat patients with heart failure.

Seasonal acclimation in cardiac activity: Mammals vs. fish

The dominance of vagal tonus over cardiac sympathetic tone is accentuated on acute cold exposure of mammals to a core temperature of 25 °C, leading to a bradycardia appropriate for the reduction in metabolic rate. When investigated by Power Spectral Analysis, changes in heart rate variability (HRV) can be seen as a decrease in the ratio of low frequency to high frequency (LF:HF) power in rats. In hamsters this only occurs after a period of cold acclimation to an environmental temperature of 4 °C, whilst maintaining core temperature. Interestingly, despite ∼30% cardiac hypertrophy on chronic cold exposure, the power output of acclimated hamster hearts (either rate-pressure product, or dP/dt) is less than those from euthermic controls, although less temperature-sensitive. Acclimation of common carp to similar environmental temperatures leads to a commensurate drop in core temperature, with a similar degree of cardiac hypertrophy. In this case, heart rate varied directly with oxygen consumption, although HR decreased and HRV increased in a non-linear manner between 25 and 5 °C on chronic exposure. Interestingly, acute changes in temperature resulted in a decrease in vagal tone on warming, but no significant change on cooling. Pharmacological blockade shows both chronic and acute responses to be dominated by cholinergic influences, with little role for adrenergic control. Supported by NERC.

Mechanisms of reduced mitochondrial Ca2+ accumulation in failing hamster heart

Mitochondrial Ca(2+) plays important roles in the regulation of energy metabolism and cellular Ca(2+) homeostasis. In this study, we characterized mitochondrial Ca(2+) accumulation in Syrian hamster hearts with hereditary cardiomyopathy (strain BIO 14.6). Exposure of isolated mitochondria from 70 nM to 30 microM Ca(2+) ([Ca(2+)](o)) caused a concentration-dependent increase in intramitochondrial Ca(2+) concentrations ([Ca(2+)](m)). The [Ca(2+)](m) was significantly lower in cardiomyopathic (CMP) hamsters than in healthy hamsters when [Ca(2+)](o) was higher than 1 microM and a decrease of about 52% was detected at [Ca(2+)](o) of 30 microM (916 +/- 67 nM vs 1,932 +/- 132 nM in control). A possible mechanism responsible for the decreased mitochondrial Ca(2+) uptake in CMP hamsters is the depolarization of mitochondrial membrane potential (Delta psi (m)). Using a tetraphenylphosphonium (TPP(+)) electrode, the measured Delta psi (m) in failing heart mitochondria was -136 +/- 1.5 mV compared with -159 +/- 1.3 mV in controls. Analyses of mitochondrial respiratory chain demonstrated a significant impairment of complex I and complex IV activities in failing heart mitochondria. In summary, a less negative Delta psi (m) resulting from defects in the respiratory chain may lead to attenuated mitochondrial Ca(2+) accumulation, which in turn may contribute to the depressed energy production and myocardial contractility in this model of heart failure. In addition to other known impairments of ion transport in sarcoplasmic reticulum and plasma membrane, results from this paper on mitochondrial dysfunctions expand our understanding of the molecular mechanisms leading to heart failure.

Induction of regulatory cells and control of cellular but not vascular rejection by costimulation blockade in hamster‐to‐rat heart xenotransplantation

In heart allograft in the rat, a sustained costimulation blockade with CTLA4Ig prevents alloreactive T-cell activation and promotes a long-term graft survival through the action of tolerogeneic dendritic cells. It is unclear whether similar mechanisms might occur after xenotransplantation. To test that hypothesis, we have analyzed the action of CTLA4Ig in a model of CD4(+)T cell-mediated xenograft rejection. Hamster hearts were transplanted into LEW.1A rats receiving an accommodation-inducing treatment consisting of a short course administration of LF15-0195 and a daily administration of cyclosporine A (CSA). To achieve long-term delivery of CTLA4Ig, an intravenous administration of an adenovirus vector coding for mouse CTLA4Ig (Ad-CTLA4Ig) was added to the accommodation induction protocol. On day 40 post-transplantation, rejection was induced by CSA withdrawal. In other xenograft recipients, CD28/B7 costimulation was inhibited at that time only by injections of CTLA4Ig or anti-CD28 antibodies. Graft survival, immunohistology, as well as development of antibodies and regulatory cells were examined. Xenografts survived 6 days after CSA withdrawal in controls and were rejected, as previously described, through the action of CD4(+) xenoreactive T cells. Interfering with CD28/B7 costimulation inhibited this xenoreactive T cell response and delayed rejection to day 10. In recipients that had received Ad-CTLA4Ig, survival was prolonged to day 19 and this was accompanied by the appearance of regulatory cells exhibiting non-donor-specific suppressive activity dependent on IL-2, NO, and IDO. These regulatory cells were different from those previously identified after Ad-CTLA4Ig administration in heart allograft in the rat. In these recipients, rejection occurred as a consequence of an evoked anti-donor IgM response and complement activation and not of a cellular rejection as complement inhibition with cobra venom factor further prolonged xenograft survival. CD28/B7 blockade delays CD4(+) T cell-mediated rejection after CSA withdrawal in accommodated recipients of hamster heart xenografts. In addition, a sustained expression of CTLA4Ig has the potential of inducing cellular regulatory mechanisms. However, such treatment does not prevent the development of xenoreactive IgM antibodies that participate in vascular rejection processes in a complement-dependent manner.

Response of the xenograft endothelium in the concordant xenotransplantation

Objective To investigate the response of the xenograft endothelium in the concordant hamster to rat cardiac xenotransplantation and the mechanism of acute vascular rejection. Methods The animals were divided into 5 groups randomly: control group. CsA group, splenectomy group, D0 splenectomy+CsA group and D3 splenectomy+CsA group. Hamster heart was heterotopicaly transplanted to rat abdominal cavity. The graft survival was monitored by palpation of the rat abdominal wall. The histological and ultrastructural changes of the xenogafts were investigated. NF-κB and P-selectin expression in the xenograft were detected. Heme Oxigenase-1 and Bcl-2 expression were also detected in the xenografts of different groups. Results The mean survival time of the xenografts in control group, CsA group, splenectomy group, D0 splenectomy+CsA group and D3 splenectomy+CsA group was 3.4 ± 0.55, 3.8 ± 0.45, 6.4 ± 1.52, 30 and 7.4 ± 1.14 days. The rejected graft showed typical acute vascular rejection in control group, CsA group, splenectomy group and D3 splenectomy+CsA group. Fndothelial cells of the rejected xenograft showed dramatic assembly of ribosomes and expansion of the rough endoplasmic reticulum. However, the endothelium of the long-term survived grafts in D0 splenectomy+CsA group showed normal architecture. NF-κB and P-selectin expression were detected in the rejected xenografts. HO-1 expression was observed in the long-term survived xenografts in D0 splenectomy+CsA group. Conclusion The endothelial cells of the xenograft might be activated during the acute vascular rejection. Expression of HO-1 might inhibit the upregulation of NF-κB and adhesion molecular which decreases the activation of the endothelium of the graft.

Beneficial Effects of the Dual L- and T-Type Ca2+ Channel Blocker Efonidipine on Cardiomyopathic Hamsters

The T-type Ca2+ channel (TCC) is activated, and abnormalities of the TCC may be related to the pathogenesis of Ca2+ overload, in cardiomyopathic hamster hearts. The aims of the present study were to investigate the alteration in expression of the TCC and to examine the effects of a dual L-and T-type Ca2+ channel blocker, efonidipine (EFO), on cardiac function and TCC during development of heart failure in UM-X7.1 cardiomyopathic hamsters. UM-X7.1 and golden hamsters were examined, and EFO was administered at the age of 20 weeks for 4 weeks. Cardiac function was examined, the expression of TCCalpha1G was measured, and ventricular myocytes were subjected to a patch-clamp study. At 24 weeks, vehicle-treated UM-X7.1 hamsters exhibited significant increases in left ventricular (LV) size, with marked decreases in ejection fraction (LVEF) compared with golden hamsters. In the UM-X7.1 group, the expression of TCCalpha1G increased during development of heart failure compared with the golden hamster group. In the UM-X7.1 group, EFO treatment significantly attenuated the decrease of LVEF without affecting blood pressure compared with the vehicle group. EFO treatment decreased heart rate (by approximately 10%) in both groups. In the golden hamster group, EFO treatment did not affect LV function. The TCC current in ventricular myocytes was significantly increased in UM-X7.1, and was inhibited by EFO in a dose-dependent manner. In cardiomyopathic hamster hearts, abnormalities in the TCC may be at least in part related to the pathogenesis of abnormal Ca2+ homeostasis, and TCC-blocker treatment may decrease the TCC current, resulting in an improvement of cardiac function. TCC blocker therapy might be a new strategy for certain types of heart failure.

Cytokine production during the inhibition of acute vascular rejection in a concordant hamster-to-rat cardiac xenotransplantation model

The aim of the current study was to investigate the role of interleukin (IL)-2, interferon (IFN)-gamma, IL-4 and IL-10 in a concordant hamster-to-rat cardiac xenotransplantation model. A hamster-to-rat cardiac transplantation was performed using SD rats as recipients of Golden Syrian hamster hearts. A total of 60 SD rats were divided into four groups and treated as follows: control group (n = 15); splenectomy group (n = 15); CsA group (n = 15); CsA + splenectomy group (n = 15). Levels of IL-2, IFN-gamma, IL-4 and IL-10 were measured by enzyme linked immunosorbent assay (ELISA). Sera were harvested at different time points in each group: day 1, and 3 as well as the day the xenograft stopped beating in the control group and CsA group; day 1, 3, 7, 14 and 30 in the splenectomy group and CsA + splenectomy group. The expression of P-selectin and intercellular adhesion molecule-1 (ICAM-1) was examined by immunohistochemical analysis of the xenograft after cardiac xenotransplantation. Serum levels of IL-2 and IFN-gamma were upregulated in untreated (day 3) and splenectomy-treated animals (day 7) compared to CsA + splenectomy treated animals (day 7). IL-10 was upregulated in long-term survival recipients following splenectomy + CsA. Neither P-selectin nor ICAM-1 expression was detected in long-term survival xenografts. Serum IL-2 and IFN-gamma were elevated following acute vascular rejection. Serum IL-10 was correlated to immunosuppression and protective effects in long-term survival rats following concordant cardiac xenotransplantation.

α-Linolenic Acid-Enriched Diet Prevents Myocardial Damage and Expands Longevity in Cardiomyopathic Hamsters

Randomized clinical trials have demonstrated that the increased intake of omega-3 polyunsaturated fatty acids significantly reduces the risk of ischemic cardiovascular disease, but no investigations have been performed in hereditary cardiomyopathies with diffusely damaged myocardium. In the present study, delta-sarcoglycan-null cardiomyopathic hamsters were fed from weaning to death with an alpha-linolenic acid (ALA)-enriched versus standard diet. Results demonstrated a great accumulation of ALA and eicosapentaenoic acid and an increased eicosapentaenoic/arachidonic acid ratio in cardiomyopathic hamster hearts, correlating with the preservation of myocardial structure and function. In fact, ALA administration preserved plasmalemma and mitochondrial membrane integrity, thus maintaining proper cell/extracellular matrix contacts and signaling, as well as a normal gene expression profile (myosin heavy chain isoforms, atrial natriuretic peptide, transforming growth factor-beta1) and a limited extension of fibrotic areas within ALA-fed cardiomyopathic hearts. Consequently, hemodynamic indexes were safeguarded, and more than 60% of ALA-fed animals were still alive (mean survival time, 293+/-141.8 days) when all those fed with standard diet were deceased (mean survival time, 175.9+/-56 days). Therefore, the clinically evident beneficial effects of omega-3 polyunsaturated fatty acids are mainly related to preservation of myocardium structure and function and the attenuation of myocardial fibrosis.

Abstract 566: Altered Expression of Connexin43 Contributes to the Arrhythmogenic Substrate in Early Stage Heart Failure of Cardiomyopathic Hamster

Background: Heart failure is known to predispose life-threatening ventricular tachyarrhythmias even before compromising the systemic circulation, but the underlying mechanism is not well understood. Methods and Results : We investigated stage-dependent changes in connexin43 (Cx43) expression and consequent electrophysiological properties in UM-X7.1 cardiomyopathic hamster hearts. UM-X7.1 hamsters develop left ventricular (LV) hypertrophy by age 6~10w, and show more pronounced LV hypertrophy and a moderate reduction in LV contractility at age 20w. Appreciable interstitial fibrosis is recognized at these stages. LV mRNA and protein levels of Cx43 in UM-X7.1 were unaffected at 10w, but significantly reduced at 20w (by 33% and 55%, respectively from controls). The relative expression level of serin255-phosphorylated Cx43 was markedly increased in UM-X7.1 at age 20w (by 175%). Electrophysiological properties were examined by optical mapping. In UM-X7.1 at 10w, almost normal LV conduction was preserved, whereas the dispersion of action potential duration (APD) was significantly increased. UM-X7.1 at 20w showed significant reduction of conduction velocity (by 35~40%), significant prolongation of APD (by 68%), marked distortion of activation fronts and a pronounced increase in APD dispersion. Programmed stimulation resulted in no arrhythmias in controls, but sustained ventricular tachycardia or fibrillation (VT/VF &gt;5s) in UM-X7.1 (1/11 at 10w and 5/6 at 20w). LV activation during polymorphic VT was characterized by multiple phase singularities or wavebreaks. Conclusions : In the early stage heart failure of cardiomyopathy, down-regulation and serine255-phosphorylation of Cx43 in addition to the interstitial fibrosis may contribute to the arrhythmogenic substrate through the inhibition of cell-to-cell communication.

Role of Oxidative/Nitrosative Stress in the Tolerance to Ischemia/Reperfusion Injury in Cardiomyopathic Hamster Heart

We investigated the role of oxidative/nitrosative stress in the tolerance to ischemia/reperfusion (I/R) injury in BIO14.6 cardiomyopathy hamster hearts at 6 weeks of age. These hearts showed no significant morphologic change and left ventricular (LV) dysfunction. However, expression and activity of iNOS, nitrotyrosine (NT) formation, and protein kinase C (PKC)-epsilon activity were increased in these hearts. When the BIO14.6 hamster hearts were isolated and subjected to 40 min of global ischemia, they showed smaller myocardial necrosis and greater recovery of LV function during reperfusion compared with the control hamster heart. All of these effects were abrogated by prolonged treatment with the antioxidant, 2-mercaptopropionylglycine (MPG). Brief preischemic treatment with MPG or the iNOS inhibitor 1400W also abrogated NT formation and activation of PKC-epsilon and inhibited the tolerance to I/R injury in the BIO14.6 hamster heart. Brief preischemic treatment with the PKC inhibitor chelerythrine or the K(ATP) channel blockers, 5-hydroxydecanoate (5-HD) and glibenclamide, had no effect on iNOS activation and NT formation but inhibited the tolerance to I/R injury in the cardiomyopathic heart. These results suggest that oxidative/nitrosative stress plays a role in the tolerance to I/R injury in the cardiomyopathic heart through activation of PKC and the downstream effectors, K(ATP) channels.

Renin increments the inward calcium current in the failing heart

Evidence is available that activation of the renin-angiotensin system is involved in cardiac remodeling. It is unknown whether renin can change the inward calcium current (ICa) in the failing heart. This problem was investigated in the present study. Cardiomyocytes were isolated from the ventricle of 4-month-old cardiomyopathic hamsters and measurements of the L-type ICa were performed using the patch-clamp technique in a whole-cell configuration. Extracellular renin (128 pmol Ang I/ml per min) plus angiotensinogen (110 pmol angiotensin I generated by renin to exhaustion) incremented the peak ICa density significantly, an effect suppressed by enalapril maleate (10 mol/l) or by losartan (10 mol/l) added to the bath, indicating that the effect of renin plus angiotensinogen was related to the formation of angiotensin I and its conversion to angiotensin II at the surface cell membrane. Renin internalization seems to increment the ICa because intracellular dialysis of renin (128 pmol Ang I/ml per min) plus angiotensinogen (110 pmol angiotensin I generated by renin to exhaustion) also increased the peak ICa density significantly, an effect suppressed by intracellular losartan (10 mol/l) but not by extracellular losartan (10 mol/l). Extracellular renin plus angiotensinogen increases the ICa in isolated myocytes from the failing heart of cardiomyopathic hamsters through the formation of angiotensin II and the activation of angiotensin type 1 receptors at the surface cell membrane. A similar increment of ICa was found with intracellular administration of renin plus angiotensinogen. This finding might indicate that renin internalization is involved in control of inward calcium current in the failing heart.

Heart Failure: A Silver bullet to treat heart failure

Heart failure (HF) continues to be a progressive disease with ever increasing morbidity and mortality in the western world.1 While progress in conventional treatment modalities is making steady and incremental gains to reduce HF mortality, there remains a need to explore new and potentially therapeutic approaches.1 To that end, several animal models of heart failure have been used to test these novel therapies. A genetic strain of Syrian hamsters with a large deletion in the -sarcoglycan (SG) gene (TO-2 strain), are characterized by skeletal muscle myopathy, and severe cardiac dilation and cardiomyopathy, which primarily contributes to the very high mortality in these animals.2 In a recent study, Zhu et al.3 reported that a single injection of adeno-associated type-8 vector carrying the human -SG gene enhanced contractile function in the hearts of these diseased hamsters, restored exercise capacity and survival to normal, and improved skeletal muscle function.

Beneficial Effect of Eplerenone on Cardiac Remodelling and Electrical Properties of the Failing Heart

The effect of chronic administration of eplerenone on cardiac remodelling and electrical properties was investigated in the failing heart of cardiomyopathic hamsters (TO-2) at five months of age. Two-month-old hamsters were treated with eplerenone (200 mg/kg/day) administered into the chow for a period of three months. Measurements of membrane potential were performed with intracellular microelectrodes connected to a high impedance DC amplifier. The thickness of the ventricular wall as well as the area of fibrosis were measured. To investigate the influence of eplerenone on the electrogenic sodium pump myocytes were isolated from the ventricle and the pump current density was measured in voltage clamped cells using the whole cell clamp configuration. The results indicated that: 1) the width of the left and right ventricular wall was significantly reduced; 2) the heart weight/body weight ratio was decreased by 38+/-2.4% (n=24) (p<0.05); 3) the fibrotic area in the left ventricle (LV) was reduced by 12.6+/-2% (n=25) (p<0.05); 4) the incidence of cardiac arrhythmias was decreased from 58+/-3.8% (n=20) in the control to 40+/-4.1% (n=20) (p<0.05) in animals treated with eplerenone. Moreover, a significant reduction in the dispersion of the QT interval was found with the drug; 5) eplerenone increased the resting potential of ventricular fibres from 64.3+/-1.5 mV to 73.4+/-1.4 mV (n=30) (p<0.05), an effect related to the activation of an electrogenic sodium pump. The conduction velocity, in longitudinal direction, was enhanced from 50+/-2.2 cm/s (n=10) in the controls to 59+/-2.4 cm/s (n=13) (p<0.05) in animals treated with eplerenone. Eplerenone reduces cardiac remodelling, the incidence of cardiac arrhythmias and improves impulse propagation, an effect in part related to the antifibrotic effect of the drug but also to the activation of the electrogenic sodium pump.