Cardiomyopathic Human Hearts Research Articles

Towards automated assessment of drug efficacy on cardiomyopathic human heart function.

Structural and functional abnormalities of ventricular myocardium related to Hypertrophic and Dilated Cardiomyopathies (HCM and DCM) are commonly caused by inherited mutations in sarcomeric proteins. Automating predictions of mutation and drug effects on human cardiac muscle function could enhance early diagnosis and evaluation of response to treatments for cardiomyopathies. However, the development of automation tools that integrate results from multiple experiments, conducted under various experimental conditions at different time and spatial scales from multiple species, is a significant challenge. Such automation tools usually require large sets of training data, which are extremely limited or even nonexistent from humans, thus any information generated could be significantly inaccurate or even misleading. Recent advances in multiscale computational tools, coupled with multiple experiments, for the translation of data concerning sarcomere level molecular interactions, including the effect of drugs, to the level of cardiac muscle fibers and tissues, might provide the most relevant approach for generating databases for automation algorithms. Using the MUSICO platform for precise modeling of protein-protein interactions and Ca2+ regulation in cardiac muscle cells, coupled with the finite element (FE) solver Mexie via Mijailovich-Prodanovic surrogate model, we can simulate experimental data from various sources. These tools collectively enable quantitative assessment of the changes in human cardiac muscle contractile responses caused by HCM and DCM extending from the molecular level to whole organ function, as well as prediction of improvements of cardiac muscle function by drugs. Our simulations successfully predicted pressure and volume changes due to troponin-C mutations and the effect of drugs, disopyramide and digoxin, in improving heart function in HCM and DCM, respectively, during multiple heartbeats in human heart. These simulations can potentially provide sufficient information for physicians to evaluate the progress of disease and the efficacy of administrated therapeutics.

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Altered expression of genes for Kir ion channels in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a multifactorial disease characterized by left ventricular dilation that is associated with systolic dysfunction and increased action potential duration. The Kir2.x K⁺ channels (encoded by KCNJ genes) regulate the inward rectifier current (IK1) contributing to the final repolarization in cardiac muscle. Here, we describe the transitions in the gene expression profiles of 4 KCNJ genes from healthy or dilated cardiomyopathic human hearts. In the healthy adult ventricles, KCNJ2, KCNJ12, and KCNJ4 (Kir2.1-2.3, respectively) genes were expressed at high levels, while expression of the KCNJ14 (Kir2.4) gene was low. In DCM ventricles, the levels of Kir2.1 and Kir2.3 were upregulated, but those of Kir2.2 channels were downregulated. Additionally, the expression of the DLG1 gene coding for the synapse-associated protein 97 (SAP97) anchoring molecule exhibited a 2-fold decline with increasing age in normal hearts, and it was robustly downregulated in young DCM patients. These adaptations could offer a new aspect for the explanation of the generally observed physiological and molecular alterations found in DCM.

Doxorubicin induces senescence and impairs function of human cardiac progenitor cells

The increasing population of cancer survivors faces considerable morbidity and mortality due to late effects of the antineoplastic therapy. Cardiotoxicity is a major limiting factor of therapy with doxorubicin (DOXO), the most effective anthracycline, and is characterized by a dilated cardiomyopathy that can develop even years after treatment. Studies in animals have proposed the cardiac progenitor cells (CPCs) as the cellular target responsible for DOXO-induced cardiomyopathy but the relevance of these observations to clinical settings is unknown. In this study, the analysis of the DOXO-induced cardiomyopathic human hearts showed that the majority of human CPCs (hCPCs) was senescent. In isolated hCPCs, DOXO triggered DNA damage response leading to apoptosis early after exposure, and telomere shortening and senescence at later time interval. Functional properties of hCPCs, such as migration and differentiation, were also negatively affected. Importantly, the differentiated progeny of DOXO-treated hCPCs prematurely expressed the senescence marker p16(INK4a). In conclusion, DOXO exposure severely affects the population of hCPCs and permanently impairs their function. Premature senescence of hCPCs and their progeny can be responsible for the decline in the regenerative capacity of the heart and may represent the cellular basis of DOXO-induced cardiomyopathy in humans.

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Repression of miR‐142 by p300 and MAPK is required for survival signalling via gp130 during adaptive hypertrophy

An increase in cardiac workload, ultimately resulting in hypertrophy, generates oxidative stress and therefore requires the activation of both survival and growth signal pathways. Here, we wanted to characterize the regulators, targets and mechanistic roles of miR-142, a microRNA (miRNA) negatively regulated during hypertrophy. We show that both miRNA-142-3p and -5p are repressed by serum-derived growth factors in cultured cardiac myocytes, in models of cardiac hypertrophy in vivo and in human cardiomyopathic hearts. Levels of miR-142 are inversely related to levels of acetyltransferase p300 and MAPK activity. When present, miR-142 inhibits both survival and growth pathways by directly targeting nodal regulators p300 and gp130. MiR-142 also potently represses multiple components of the NF-κB pathway, preventing cytokine-mediated NO production and blocks translation of α-actinin. Forced expression of miR-142 during hypertrophic growth induced extensive apoptosis and cardiac dysfunction; conversely, loss of miR-142 fully rescued cardiac function in a murine heart failure model. Downregulation of miR-142 is required to enable cytokine-mediated survival signalling during cardiac growth in response to haemodynamic stress and is a critical element of adaptive hypertrophy.

Role of K ATP Channels in the Maintenance of Ventricular Fibrillation in Cardiomyopathic Human Hearts

Ventricular fibrillation (VF) leads to global ischemia. The modulation of ischemia-dependent pathways may alter the electrophysiological evolution of VF. We addressed the hypotheses that there is regional disease-related expression of K(ATP) channels in human cardiomyopathic hearts and that K(ATP) channel blockade promotes spontaneous VF termination by attenuating spatiotemporal dispersion of refractoriness. In a human Langendorff model, electric mapping of 6 control and 9 treatment (10 μmol/L glibenclamide) isolated cardiomyopathic hearts was performed. Spontaneous defibrillation was studied and mean VF cycle length was compared regionally at VF onset and after 180 seconds between control and treatment groups. K(ATP) subunit gene expression was compared between LV endocardium versus epicardium in myopathic hearts. Spontaneous VF termination occurred in 1 of 6 control hearts and 7 of 8 glibenclamide-treated hearts (P=0.026). After 180 seconds of ischemia, a transmural dispersion in VF cycle length was observed between epicardium and endocardium (P=0.001), which was attenuated by glibenclamide. There was greater gene expression of all K(ATP) subunit on the endocardium compared with the epicardium (P<0.02). In an ischemic rat heart model, transmural dispersion of refractoriness (ΔERP(Transmural)=ERP(Epicardium)-ERP(Endocardium)) was verified with pacing protocols. ΔERP(Transmural) in control was 5 ± 2 ms and increased to 36 ± 5 ms with ischemia. This effect was greatly attenuated by glibenclamide (ΔERP(Transmural) for glibenclamide+ischemia=4.9 ± 4 ms, P=0.019 versus control ischemia). K(ATP) channel subunit gene expression is heterogeneously altered in the cardiomyopathic human heart. Blockade of K(ATP) channels promotes spontaneous defibrillation in cardiomyopathic human hearts by attenuating the ischemia-dependent spatiotemporal heterogeneity of refractoriness during early VF.

264 Is ventricular fibrillation different in ischemic compared to non-ischemic dilated cardiomyopathic human hearts?

It is unknown if VF dynamics are dependent on the etiology of the cardiomyopthay. In this study we compared transmural dominant frequency gradient, during ventricular fibrillation (VF), in ischemic and non-ischemic dilated cardiomyopathic human hearts. The study was conducted in human langendorff model. These were ischemic (ICM, n = 5) and dilated (DCM, n = 5) cardiomyopathic human hearts explanted from patients undergoing cardiac transplant. Data was collected using an epicardial sock and an endocardial balloon each having 112 unipolar electrodes, arranged in 14 columns and 8 rows. Ischemia was induced by halting the perfusion to the heart and VF was initiated by brief application of 9V batter to epicardium. VF was recorded at onset, 90 seconds and 180 seconds for 20 seconds each. Dominant frequency (DF) was computed using Welch periodogram method as described in our previous studies. Repeated measure ANOVA was employed using mixed model in SAS. The mean DF in LV-endocardium and LV-epicardium is reported in table 1. At the onset of VF, no difference was observed between LV epicardium and endocardium in dilated cardiomyopathic hearts (P = 0.6) while the difference was statistically significant in ischemic cardiomyopathic hearts (P < 0.05). After 180 seconds of VF, there was a significant transmural DF gradient in both ischemic and dilated cardiomyopathic hearts (P < 0.05).Tabled 1 There is a LV transmural DF gradient during VF in both DCM and ICM after 3 minutes of ischemia. This gradient is established early in ischemia in ICM but not in DCM. These finding may relate to differential transmural ion channel remodelling that is dependent of the etiology of cardiomyopathic process.

MRNA cargo no longer on time

heart failure is the most important cause of death in the Western world, and numerous attempts have been undertaken to identify the origin of this disease. Cohn et al. ([1][1]) in 2000 defined cardiac remodeling leading to heart failure as “genome expression resulting in molecular, cellular and

Beta-catenin accumulates in intercalated disks of hypertrophic cardiomyopathic hearts.

To evaluate whether cardiomyocyte membrane structure and cell/extracellular matrix adhesion alterations perturb the cadherin/catenin complex in the hypertrophic cardiomyopathy (HCM). Hypertrophic cardiomyopathic hamster (UM-X7.1 strain) and human hearts were studied by light and electron microscopy, Northern and Western blot analyses and immunohistochemistry. Intercalated disks are disorganized in both hamster and human cardiomyopathic hearts; beta-catenin is increased and accumulated in intercalated disks depriving cardiomyocyte nuclei of fundamental signals. The accumulation of beta-catenin is post-translationally regulated by an increased Wnt expression, a simultaneous decrease in glycogen synthase kinase 3beta (GSK3beta) expression and a different expression pattern of adenomatous polyposis coli (APC) isoforms. The reorganization of cell/cell adhesion in cardiomyopathic hearts is mainly contributed by the cadherin/catenin system, which is differently regulated to sustain cell structural rather than signalling needs causing considerable consequences in the determination of cardiomyocyte phenotype and clinical outcome. The accumulation of beta-catenin in intercalated disks could concur to increase myocardial wall stiffness and left ventricular end-diastolic pressure (LVEDP) in hypertrophic cardiomyopathic hamster and human hearts.

Activation of nuclear factor-kappaB is necessary for myotrophin-induced cardiac hypertrophy.

The transcription factor nuclear factor-κB (NF-κB) regulates expression of a variety of genes involved in immune responses, inflammation, proliferation, and programmed cell death (apoptosis). Here, we show that in rat neonatal ventricular cardiomyocytes, activation of NF-κB is involved in the hypertrophic response induced by myotrophin, a hypertrophic activator identified from spontaneously hypertensive rat heart and cardiomyopathic human hearts. Myotrophin treatment stimulated NF-κB nuclear translocation and transcriptional activity, accompanied by IκB-α phosphorylation and degradation. Consistently, myotrophin-induced NF-κB activation was enhanced by wild-type IκB kinase (IKK) β and abolished by the dominant-negative IKKβ or a general PKC inhibitor, calphostin C. Importantly, myotrophin-induced expression of two hypertrophic genes (atrial natriuretic factor [ANF] and c-myc) and also enhanced protein synthesis were partially inhibited by a potent NF-κB inhibitor, pyrrolidine dithio-carbamate (PDTC), and calphostin C. Expression of the dominant-negative form of IκB-α or IKKβ also partially inhibited the transcriptional activity of ANF induced by myotrophin. These findings suggest that the PKC–IKK–NF-κB pathway may play a critical role in mediating the myotrophin-induced hypertrophic response in cardiomyocytes.

Induction of oxidative stress and disintegrin metalloproteinase in human heart end-stage failure.

Collagen degradation is required for the creation of new integrin binding sites necessary for cell survival. However, a complete separation between the matrix and the cell leads to apoptosis, dilatation, and failure. Previous studies have demonstrated increased metalloproteinase activity in the failing myocardium. To test the hypothesis that disintegrin metalloproteinase (DMP) is induced in human heart end-stage failure, left ventricle tissue from ischemic cardiomyopathic (ICM, n = 10) and dilated cardiomyopathic (DCM, n = 10) human hearts were obtained at the time of orthotopic cardiac transplant. Normal (n = 5) tissue specimens were obtained from unused hearts. The levels of reduced oxygen species (ROS) were 12 +/- 2, 25 +/- 3, and 16 +/- 2 nmol (means +/- SE, P < 0.005) in normal, ICM, and DCM, respectively, by spectrofluorometry. The percent levels of endothelial cells were 100 +/- 15, 35 +/- 19, and 55 +/- 11 in normal, ICM, and DCM, respectively, by CD31 labeling. The levels of nitrotyrosine by Western analysis were significantly increased, and endothelial nitric oxide (NO) by the Griess method was decreased in ICM and DCM compared with normal tissue. The synthesis and degradation of beta(1)-integrin and connexin 43 were significantly increased in ICM and DCM compared with normal hearts by Western analysis. Levels of DMP were increased, and levels of cardiac inhibitor of metalloproteinase (CIMP) were decreased. Aggrecanase activity of DMP was significantly increased in ICM and DCM hearts compared with normal. These results suggest that the occurrence of cardiomyopathy is significantly confounded by the increase in ROS, nitrotyrosine, and DMP activity. This increase is associated with decreased NO, endothelial cell density, and CIMP. In vitro, treatment of CIMP abrogated the DMP activity. The treatment with CIMP may prevent degradation of integrin and connexin and ameliorate heart failure.

Inhibition of the cardiac electrogenic sodium bicarbonate cotransporter reduces ischemic injury.

Although it is believed that sodium-driven acid-base transport plays a central role in the development of the reperfusion injury that follows cardiac ischemia, research to date has demonstrated only a role for Na(+)/H(+) exchange (NHE). However, Na(+)-driven HCO(-)(3) transport, which is quantitatively as important as NHE in cardiac cells, has not been examined. Here the results show that a neutralizing antibody raised against the human heart electrogenic Na(+)/HCO(3)(-) cotransporter (hhNBC) blocked the recovery of pH after acidic pulse both in HEK-293 cells expressing hhNBC and in rat cardiac myocytes demonstrating the presence of an electrogenic NBC in rat cardiac myocytes similar to hhNBC. Administration of anti-NBC antibody to ischemic-reperfused rat hearts markedly protects systolic and diastolic functions of the heart during reperfusion. Furthermore, using a quantitative real-time RT-PCR (TaqMan) and Western blot analysis we demonstrated that in human cardiomyopathic hearts, mRNA and protein levels of hhNBC increase, whereas mRNA levels of the electroneutral Na(+)/HCO(3)(-) cotransporter (NBCn1) remain unchanged. Our data provide evidence that inhibition of hhNBC, whose role in cardiac pathologies could be amplified by overexpression, represents a novel therapeutic approach for ischemic heart disease.

Nitric Oxide and Cardiac Contractility in Human Heart Failure

The free radical gas nitric oxide (NO) is produced by 3 isoforms of nitric oxide synthase (NOS). All of them are present in the heart: NOS1 (nNOS, “neuronal” NOS) has been detected in cardiac conduction tissue and intracardiac neurons; NOS2 (iNOS, “cytokine-inducible” NOS) can be expressed by virtually all cells in the heart, often in conjunction with the expression of inflammatory cytokines; and finally, NOS3 (eNOS, “endothelial-constitutive” NOS) is expressed in coronary endothelium, endocardium, and cardiac myocytes. NOS3 regulates the tone of vascular smooth muscle cells; the permeability and platelet adhesion of endothelial cells; and the receptor-effector coupling, energetics, contractility, and apoptosis of cardiomyocytes.1,2 Since the original demonstration of myocardial NOS2 activity in idiopathic dilated cardiomyopathy,3 a negative inotropic effect of NO frequently was hypothesized to contribute to the depressed contractile function of failing myocardium. This hypothesis was inspired by the simultaneous publication of experimental results that showed a depressed contractile response of isolated cardiomyocytes to β-adrenergic agonists after NOS2 induction by lipopolysaccharides.4 See p 2318 To further explore this depressant action of NO on myocardial contractility, numerous experimental and clinical studies were performed, but they yielded apparently conflicting results on the inotropic effect of NO from either endogenous or pharmacological sources.2 As reported in this issue of Circulation , Cotton et al5 tackled the question of the inotropic action of NO by measuring left ventricular (LV) performance in normal control subjects and in patients with dilated cardiomyopathy during intracoronary infusion of the NOS inhibitor NG-monomethyl-l-arginine (L-NMMA). During L-NMMA infusion, Cotton et al5 observed a modest drop (14%) in LV dP/dtmax in the control group and no change in LV dP/dtmax in the cardiomyopathy group, despite myocardial expression of NOS2 in their patients. They concluded that the small …

Relationship between altered sympathetic innervation, oxidative metabolism and contractile function in the cardiomyopathic human heart; a non-invasive study using positron emission tomography.

To identify functional and metabolic correlates of impaired presynaptic sympathetic innervation in the cardiomyopathic human heart using non-invasive correlative imaging. In 10 patients with idiopathic dilated cardiomyopathy, presynaptic catecholamine uptake sites were quantified by positron emission tomography with C-11 hydroxyephedrine. Oxidative metabolism was measured using C-11 acetate. Global and regional function was assessed by tomographic radionuclide angiography. Left ventricular ejection fraction in patients was 19%+/-10%. Myocardial hydroxyephedrine retention was abnormally low in 58%+/-38% of the left ventricles. Globally and regionally, hydroxyephedrine retention was significantly correlated with ventricular function (r=0.67, P=0.03 with left ventricular ejection fraction; r=0.31, P<0.01 with regional endocardial shortening). Multivariate analysis confirmed hydroxyephedrine retention as the closest independent determinant of left ventricular ejection fraction. Oxidative metabolism was determined by rate pressure product as a measure of workload (r=0.78, P<0.01) and peripheral vascular resistance as a measure of afterload (r=-0.61, P=0.06), but did not correlate with hydroxyephedrine retention (r=0.08 for global, r=0.04 for regional parameters). Alterations of presynaptic sympathetic innervation in dilated cardiomyopathy are associated with impaired contractile function, suggesting a common pathogenetic pathway. Overall oxidative metabolism, however, was not directly correlated with these findings. Normal regulatory mechanisms for oxidative metabolism were operational.

Cardiac hypertrophy and failure: lessons learned from genetically engineered mice.

Congestive heart failure is a major and growing public health problem. Because of improved survival of myocardial infarction patients produced by thrombolytic therapy or per-cutaneous revascularization it represents the only form of cardiovascular disease with significantly increased incidence and prevalence. Clinicians view this clinical syndrome as the final common pathway of diverse pathologies such as myocardial infarction and haemodynamic overload. Insights into mechanisms for heart failure historically derived from physiological and biochemical studies which identified compensatory adaptations for the haemodynamic burden associated with the pathological condition including utilization of the Frank Starling mechanism, augmentation of muscle mass, and neurohormonal activation to increase contractility. Therapy has largely been phenomenological and designed to prevent or limit the deleterious effects of these compensatory processes. More recently insights from molecular and cell biology have contributed to a more mechanistic understanding of potential causes of cardiac hypertrophy and failure. Many different analytical approaches have been employed for this purpose. These include the use of conventional animal models which permit serial observation of the onset and progression of heart failure and a sequential analysis of underlying biochemical and molecular events. Neonatal murine cardiomyocytes have been a powerful tool to examine in vitro subcellular mechanisms devoid of the confounding functional effects of multicellular preparations and heterogeneity of cell type. Finally, significant progress has been made by utilizing tissue from human cardiomyopathic hearts explanted at the time of orthotopic transplantation. Each of these methods has significant advantages and disadvantages. Arguably the greatest advance in our understanding of cardiac hypertrophy and failure over the past decade has been the exploitation of genetically engineered mice as biological reagents to study in vivo the effects of alterations in the murine genome. The power of this approach, in principle, derives from the ability to precisely overexpress or ablate a gene of interest and examine the phenotypic consequences in a cardiac specific post-natal manner. In contrast to conventional animal models of human disease which employ some form of environmental stress, genetic engineering involves a signal known molecular perturbation which produces the phenotype.

Human eHAND, but not dHAND, is Down-regulated in Cardiomyopathies

The progression of cardiomyopathy to congestive heart failure is often associated with the expression of fetal cardiac-specific genes. In mice, the basic helix-loop-helix transcription factors, dHAND and eHAND, are expressed in a cardiac chamber-specific fashion and are essential for fetal cardiac development, but are down-regulated in the adult. Their expression in specific chambers of healthy and diseased human hearts has not been studied previously. HumandHAND and eHAND were mapped to human chromosomes 4q33 and 5q33, respectively, by fluorescent in situ hybridization. RNA from the four chambers of healthy human adult hearts, and from hearts of patients with several forms of cardiomyopathy, was obtained and assayed for dHAND and eHAND expression. Unlike in mice, dHAND expression was observed in all four chambers of the healthy human adult heart, but was diminished in the right atrium. In contrast,eHAND was expressed in the right and left ventricles, but was downregulated in both atrial chambers. We examined tissue from 15 human cardiomyopathic hearts obtained during cardiac transplantation or by endomyocardial biopsy for alterations inHAND gene expression. dHAND expression was unchanged in all forms of cardiomyopathy tested. However, cardiac expression of eHAND was severely down-regulated in six of six patients with ischemic cardiomyopathy and six of six patients with dilated cardiomyopathy. This study demonstrates that human dHAND and eHAND have unique spatial patterns of expression within human cardiac chambers. Downregulation of eHAND in ischemic and dilated cardiomyopathy suggests a correlation between eHAND dysregulation and the evolution of a subset of cardiomyopathies.

Regional pre- and postsynaptic sympathetic system in the failing human heart--regulation of beta ARK-1.

Regional presynaptic sympathetic innervation varies considerably in the cardiomyopathic human heart, as shown in previous studies in vivo and in vitro. The goal of the present study was to correlate markers of presynaptic sympathetic innervation with local measurement of the postsynaptic beta-adrenergic system in failing human hearts. In nine left ventricular regions of hearts explanted from patients suffering from dilated cardiomyopathy, we measured the density of uptake(1) carriers ([3H]mazindol binding) as a marker of presynaptic function as well as beta-receptor density ([3H]CGP 12177 binding) and beta ARK-1 levels as the pivotal compounds of postsynaptic adrenergic signal transduction. Additionally, a subgroup of the patients was examined in vivo by HED-PET prior to heart transplantation. The density of uptake(1) was related to local hydroxyephedrine (HED) retention (as determined by pre-operative PET, r=0.65), whereas it was inversely correlated to regional beta ARK-1 levels (r=-0.61, P=0.04). In contrast, beta-adrenergic receptor density was not significantly correlated either to uptake(1) density or to local HED retention (r=0.15 and r=0.21). Regional beta ARK-1 levels rather than beta-adrenergic receptor density were correlated with presynaptic alterations in cardiomyopathic human left ventricles. It can be assumed that in the cardiomyopathic human heart, regional beta-adrenergic desensitization might be determined by differences in local beta ARK levels rather than by changes in beta-receptor density.

The internal and external protein scaffold of the T-tubular system in cardiomyocytes.

The transverse tubule system of the cardiomyocyte remains undeformed despite the extreme forces it undergoes during the contraction-relaxation cycle, but the morphological basis for its stability remains unclear. Therefore, we have investigated the architecture and subcellular protein scaffold of the cardiac T-tubules and compared it with that of the costameres and of the free sarcolemma. Tissue samples from normal rat and monkey hearts, and left ventricular tissue from normal and cardiomyopathic human hearts obtained at transplantation surgery were investigated using immunocytochemistry and confocal microscopy and by electron microscopy. In addition, we used a re-differentiation model of isolated, cultured adult rat cardiomyocytes. The cell membrane of the cardiac T-tubules was found to contain the cell-matrix focal adhesion molecules (FAMs) vinculin, talin, the alpha5beta1 integrin and the membrane-associated proteins (MAPs) dystrophin and spectrin. FAMs and MAPs were localized in the T-tubular membrane in a similar pattern: in longitudinally oriented myocytes as transverse punctate lines at the Z-level; in transversally cut myocytes a radial tubular network was found to extend throughout the interior of the cell. Immunolabeling for basement membrane components including collagen IV, fibronectin and laminin showed a colocalization with FAMs and MAPs parallel to the transverse T-tubules. The costameres of the sarcolemma showed a protein composition resembling that of the T-tubules but the intervening segments of free sarcolemma showed absence of FAMs and presence of MAPs. For the first time, we demonstrate the existence and protein composition of the T-tubular scaffold in the human heart. Furthermore, we show that cardiomyocytes from human failing hearts have less abundant but more dilated T-tubules than do experimental animals. These results indicate that the cardiac T-tubular system contains a subcellular scaffold closely resembling that of the costameres. It consists of FAMs, MAPs and basal lamina proteins that confer structural integrity to the cardiac T-tubular membrane during contraction/relaxation cycles.

Regional in vivo and in vitro characterization of autonomic innervation in cardiomyopathic human heart.

In contrast to healthy volunteers, regional differences of cardiac autonomic innervation have been described through the use of C11-hydroxyephedrine positron emission tomography (HED-PET) in the left ventricles of patients with dilated cardiomyopathy. The goal of the present study was to correlate HED-PET images with biochemical analysis of tissue samples. To assess the significance of altered HED uptake, we used HED-PET to examine eight patients with dilated cardiomyopathy before heart transplantation. After explantation, we measured the density and affinity of uptake1 (3H-mazindol binding) and tissue norepinephrine content as markers of presynaptic function, and we determined beta-receptor density and affinity (3H-CGP 12177 binding) in the corresponding areas of the same patients. The density of uptake1 and norepinephrine content showed marked regional variation, with highest values in the anterior septal wall and lowest in inferoapical and apical areas. Both parameters were closely correlated (r=.65, P=.05). Similarly, uptake1 density or norepinephrine content and HED retention (PET) showed clear correlations (r=.63 and .60, respectively). Uptake1 affinities did not vary significantly and were not correlated to the other parameters. Beta-Adrenergic receptor density showed some, albeit less pronounced, regional variation and was weakly correlated to uptake1 density and local HED retention (r=.38 and .31, respectively). Uptake1 density and tissue norepinephrine content showed marked regional variation in cardiomyopathic left ventricles. HED-PET is significantly correlated to the density but not the affinity of uptake1 sites in the human heart, suggesting either loss of neurons or downregulation of uptake1 in dilated cardiomyopathy. HED-PET is a valuable marker for alterations of the presynaptic sympathoadrenergic system in humans.