Endothelin receptors in the failing and nonfailing human heart

Involvement of Histamine 2 Receptor in Alpha 1 Adrenoceptor Mediated Cardiac Hypertrophy and Oxidative Stress in H9c2 Cardio Myoblasts

Despite the involvement of ɑ1adrenergic (ɑ1AR) and Histamine 2 receptors (H2R) in cardiac hypertrophy (CH), their relationship is yet to be studied. Our study investigated interrelationship between them using in vitro CH model. H9c2 cardiomyoblasts were exposed to phenylephrine (ɑ1AR agonist-50 μM) in the presence, the absence of famotidine (H2R antagonist-10 μM) and BAY 11-7082 (NF-kB inhibitor-10 μM). The impact of ɑ1AR stimulation on H2R expression and oxidative stress was assessed. Hypertrophic indices were assessed from activities of enzymatic mediators of cardiac hypertrophy, total protein content, BNP levels and cell volume. Additionally, the inverse agonistic property of famotidine and NFkB activity was also studied. ɑ1AR-induced H2R expression, oxidative stress and hypertrophic indices were significantly abolished by famotidine and pharmacological inhibitor of NFkB. Increase in constitutive activity of H2R was noticed correlating with increased receptor population. These results suggest involvement of NFkB-mediated upregulation of H2R in ɑ1AR-mediated CH.

Targeting Endothelin Receptors in a Murine Model of Myocardial Infarction Using a Small Molecular Fluorescent Probe

The endothelin (ET) axis plays a pivotal role in cardiovascular diseases. Enhanced levels of circulating ET-1 have been correlated with an inferior clinical outcome after myocardial infarction (MI) in humans. Thus, the evaluation of endothelin-A receptor (ET_AR) expression over time in the course of myocardial injury and healing may offer valuable information toward the understanding of the ET axis involvement in MI. We developed an approach to track the expression of ET_AR with a customized molecular imaging probe in a murine model of MI. The small molecular probe based on the ET_AR-selective antagonist 3-(1,3-benzodioxol-5-yl)-5-hydroxy-5-(4-methoxyphenyl)-4-[(3,4,5-trimethoxyphenyl)methyl]-2(5H)-furanone (PD156707) was labeled with fluorescent dye, IRDye800cw. Mice undergoing permanent ligation of the left anterior descending artery (LAD) were investigated at day 1, 7, and 21 post surgery after receiving an intravenous injection of the ET_AR probe. Cryosections of explanted hearts were analyzed by cryotome-based CCD, and fluorescence reflectance imaging (FRI) and fluorescence signal intensities (SI) were extracted. Fluorescence-mediated tomography (FMT) imaging was performed to visualize probe distribution in the target region in vivo. An enhanced fluorescence signal intensity in the infarct area was detected in cryoCCD images as early as day 1 after surgery and intensified up to 21 days post MI. FRI was capable of detecting significantly enhanced SI in infarcted regions of hearts 7 days after surgery. In vivo imaging by FMT localized enhanced SI in the apex region of infarcted mouse hearts. We verified the localization of the probe and ET_AR within the infarct area by immunohistochemistry (IHC). In addition, neovascularized areas were found in the affected myocardium by CD31 staining. Our study demonstrates that the applied fluorescent probe is capable of delineating ET_AR expression over time in affected murine myocardium after MI in vivo and ex vivo.

Transition from post-capillary pulmonary hypertension to combined pre- and post-capillary pulmonary hypertension in swine: a key role for endothelin

Key points

Passive, isolated post‐capillary pulmonary hypertension (PH) secondary to left heart disease may progress to combined pre‐ and post‐capillary or ‘active’ PH

This ‘activation’ of post‐capillary PH significantly increases morbidity and mortality, and is still incompletely understood.

In this study, pulmonary vein banding gradually produced post‐capillary PH with structural and functional microvascular remodelling in swine.

Ten weeks after banding, the pulmonary endothelin pathway was upregulated, likely contributing to pre‐capillary aspects in the initially isolated post‐capillary PH.

Inhibition of the endothelin pathway could potentially stop the progression of early stage post‐capillary PH.

Abstract

Passive, isolated post‐capillary pulmonary hypertension (IpcPH) secondary to left heart disease may progress to combined pre‐ and post‐capillary or ‘active’ PH (CpcPH) characterized by chronic pulmonary vascular constriction and remodelling. The mechanisms underlying this ‘activation’ of passive pulmonary hypertension (PH) remain incompletely understood. Here we investigated the role of the vasoconstrictor endothelin‐1 (ET) in the progression from IpcPH to CpcPH in a swine model for post‐capillary PH. Swine underwent pulmonary vein banding (PVB; n = 7) or sham‐surgery (Sham; n = 6) and were chronically instrumented 4 weeks later. Haemodynamics were assessed for 8 weeks, at rest and during exercise, before and after administration of the ET receptor antagonist tezosentan. After sacrifice, the pulmonary vasculature was investigated by histology, RT‐qPCR and myograph experiments. Pulmonary arterial pressure and resistance increased significantly over time. mRNA expression of prepro‐endothelin‐1 and endothelin converting enzyme‐1 in the lung was increased, while ET_A expression was unchanged and ET_B expression was downregulated. This was associated with increased plasma ET levels from week 10 onward and a more pronounced vasodilatation to in vivo administration of tezosentan at rest and during exercise. Myograph experiments showed decreased endothelium‐dependent vasodilatation to Substance P and increased vasoconstriction to KCl in PVB swine consistent with increased muscularization observed with histology. Moreover, maximal vasoconstriction to ET was increased whereas ET sensitivity was decreased. In conclusion, PVB swine gradually developed PH with structural and functional vascular remodelling. From week 10 onward, the pulmonary ET pathway was upregulated, likely contributing to pre‐capillary activation of the initially isolated post‐capillary PH. Inhibition of the ET pathway could thus potentially provide a pharmacotherapeutic target for early stage post‐capillary PH.

Passive, isolated post‐capillary pulmonary hypertension (PH) secondary to left heart disease may progress to combined pre‐ and post‐capillary or ‘active’ PH

This ‘activation’ of post‐capillary PH significantly increases morbidity and mortality, and is still incompletely understood.

In this study, pulmonary vein banding gradually produced post‐capillary PH with structural and functional microvascular remodelling in swine.

Ten weeks after banding, the pulmonary endothelin pathway was upregulated, likely contributing to pre‐capillary aspects in the initially isolated post‐capillary PH.

Inhibition of the endothelin pathway could potentially stop the progression of early stage post‐capillary PH.

Subcellular compartmentalization of proximal Gαq-receptor signaling produces unique hypertrophic phenotypes in adult cardiac myocytes

G protein-coupled receptors that signal through Gα_q (G_q receptors), such as α₁-adrenergic receptors (α₁-ARs) or angiotensin receptors, share a common proximal signaling pathway that activates phospholipase Cβ1 (PLCβ1), which cleaves phosphatidylinositol 4,5-bisphosphate (PIP₂) to produce inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol. Despite these common proximal signaling mechanisms, G_q receptors produce distinct physiological responses, yet the mechanistic basis for this remains unclear. In the heart, G_q receptors are thought to induce myocyte hypertrophy through a mechanism termed excitation-transcription coupling, which provides a mechanistic basis for compartmentalization of calcium required for contraction versus IP₃-dependent intranuclear calcium required for hypertrophy. Here, we identified subcellular compartmentalization of G_q-receptor signaling as a mechanistic basis for unique G_q receptor-induced hypertrophic phenotypes in cardiac myocytes. We show that α₁-ARs co-localize with PLCβ1 and PIP₂ at the nuclear membrane. Further, nuclear α₁-ARs induced intranuclear PLCβ1 activity, leading to histone deacetylase 5 (HDAC5) export and a robust transcriptional response (i.e. significant up- or down-regulation of 806 genes). Conversely, we found that angiotensin receptors localize to the sarcolemma and induce sarcolemmal PLCβ1 activity, but fail to promote HDAC5 nuclear export, while producing a transcriptional response that is mostly a subset of α₁-AR-induced transcription. In summary, these results link G_q-receptor compartmentalization in cardiac myocytes to unique hypertrophic transcription. They suggest a new model of excitation-transcription coupling in adult cardiac myocytes that accounts for differential G_q-receptor localization and better explains distinct physiological functions of G_q receptors.

Influence of Mechanical Circulatory Support on Endothelin Receptor Expression in Human Left Ventricular Myocardium from Patients with Dilated Cardiomyopathy (DCM)

Background

In terminal failing hearts ventricular assist devices (VAD) are implanted as a bridge to transplantation. Endothelin receptor (ETR) antagonists are used for treatment of secondary pulmonary hypertension in VAD patients. However, the cardiac ETR regulation in human heart failure and during VAD support is incompletely understood.

Methods

In paired left ventricular samples of 12 dilated cardiomyopathy patients we investigated the density of endothelin A (ET_A) and B (ET_B) receptors before VAD implantation and after device removal. Left ventricular samples of 12 non-failing donor hearts served as control. Receptor quantification was performed by binding of [¹²⁵I]-ET-1 in the presence of nonselective and ET_A selective ETR ligands as competitors. Additionally, the ETR mRNA expression was analyzed using quantitative real-time-PCR.

Results

The mRNA of ET_A but not ET_B receptors was significantly elevated in heart failure, whereas total ETR density analyzed by radioligand binding was significantly reduced due to ET_B receptor down regulation. ET_A and ET_B receptor density showed poor correlation to mRNA data (spearman correlation factor: 0.43 and 0.31, respectively). VAD support had no significant impact on the density of both receptors and on mRNA expression of ET_A whereas ET_B mRNA increased during VAD. A meta-analysis reveals that the ET_A receptor regulation in human heart failure appears to depend on non-failing hearts.

Conclusions

In deteriorating hearts of patients suffering from dilated cardiomyopathy the ET_A receptor density is not changed whereas the ET_B receptor is down regulated. The mRNA and the proteins of ET_A and ET_B show a weak correlation. Non-failing hearts might influence the interpretation of ET_A receptor regulation. Mechanical unloading of the failing hearts has no impact on the myocardial ETR density.

A Myocardial Slice Culture Model Reveals Alpha-1A-Adrenergic Receptor Signaling in the Human Heart

The authors used 52 nonfailing and failing human hearts to develop a simple, high throughput left ventricular myocardial slice model that is stable by ATP and viability assays for at least 3 days. The model supports studies of signaling, contraction, and viral transduction. They use the model to show for the first time that the alpha-1A-adrenergic receptor, which is present at very low abundance in the human myocardium, activates cardioprotective ERK with nanomolar EC50 in failing heart slices and stimulates a positive inotropic effect. This model should be useful for translational studies, to test whether molecules discovered in basic experiments are functional in the human heart.

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Model for translational studies

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Human LV slices

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Simple, high throughput, viable

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Assays signaling and contraction

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Supports viral transduction

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Useful for proof-of-concept in man

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Shows the α1A-AR functions in human heart

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.

Alpha-1-adrenergic receptors in heart failure: the adaptive arm of the cardiac response to chronic catecholamine stimulation

Alpha-1-adrenergic receptors (ARs) are G protein-coupled receptors activated by catecholamines. The alpha-1A and alpha-1B subtypes are expressed in mouse and human myocardium, whereas the alpha-1D protein is found only in coronary arteries. There are far fewer alpha-1-ARs than beta-ARs in the nonfailing heart, but their abundance is maintained or increased in the setting of heart failure, which is characterized by pronounced chronic elevation of catecholamines and beta-AR dysfunction. Decades of evidence from gain and loss-of-function studies in isolated cardiac myocytes and numerous animal models demonstrate important adaptive functions for cardiac alpha-1-ARs to include physiological hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Clinical trial data indicate that blocking alpha-1-ARs is associated with incident heart failure in patients with hypertension. Collectively, these findings suggest that alpha-1-AR activation might mitigate the well-recognized toxic effects of beta-ARs in the hyperadrenergic setting of chronic heart failure. Thus, exogenous cardioselective activation of alpha-1-ARs might represent a novel and viable approach to the treatment of heart failure.

Role of endothelin in uteroplacental circulation and fetal vascular function

Endothelins are 21-amino acid peptides involved in vascular homeostasis. Three types of peptide have been identified, with endothelin-1 (ET-1) being the most potent vasoconstrictor currently known. Two endothelin receptor subtypes are found in various tissues, including the brain, heart, blood vessel, lung, and placenta. The ETA-receptor is associated with vasoconstriction in vascular smooth muscle. Conversely, the ETB-receptor can elicit a vasoconstrictor effect in vascular smooth muscle and a vasodilator effect via its action in endothelial cells. Both receptors play a key role in maintaining circulatory homeostasis and vascular function. Changes in ET-1 expression are found in various disease states, and overexpression of ET-1 is observed in hypertension and preeclampsia in pregnancy. Placental localization of ET-1 implies a key role in regulating the uteroplacental circulation. Additionally, ET-1 is important in the fetal circulation and is involved in the pulmonary circulation and closure of the ductus arteriosus after birth, as well as fetal growth constriction in utero. ET receptor antagonists and nitric oxide donors may provide therapeutic potential in treating conditions associated with overexpression of ET and hypertension.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Endothelin receptor overexpression alters diastolic function in cultured rat ventricular myocytes

The endothelin (ET) signaling pathway controls many physiological processes in myocardium and often becomes upregulated in heart diseases. The aim of the present study was to investigate the effects of ET receptor upregulation on the contractile function of adult ventricular myocytes. Primary cultured adult rat ventricular myocytes were used as a model system of ET receptor overexpression in the heart. Endothelin receptor type A (ET_A) or type B (ET_B) was overexpressed by Adenoviral infection, and the twitch responses of infected ventricular myocytes were measured after ET-1 stimulation. Overexpression of ET_A exaggerated positive inotropic effect (PIE) and diastolic shortening of ET-1, and induced a new twitch response including twitch broadening. On the contrary, overexpression of ET_B increased PIE of ET-1, but did not affect other two twitch responses. Control myocytes expressing endogenous receptors showed a parallel increase in twitch amplitude and systolic Ca²⁺ in response to ET-1. However, intracellular Ca²⁺ did not change in proportion to the changes in contractility in myocytes overexpressing ET_A. Overexpression of ET_A enhanced both systolic and diastolic contractility without parallel changes in Ca²⁺. Differential regulation of this nature indicates that upregulation of ET_A may contribute to diastolic myocardial dysfunction by selectively targeting myofi lament proteins that regulate resting cell length, twitch duration and responsiveness to prevailing Ca²⁺.

Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure

Evidence from cell, animal, and human studies demonstrates that α1-adrenergic receptors mediate adaptive and protective effects in the heart. These effects may be particularly important in chronic heart failure, when catecholamine levels are elevated and β-adrenergic receptors are down-regulated and dysfunctional. This review summarizes these data and proposes that selectively activating α1-adrenergic receptors in the heart might represent a novel and effective way to treat heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Endothelin-1 and angiotensin II modulate rate and contraction amplitude in a subpopulation of mouse embryonic stem cell-derived cardiomyocyte-containing bodies

Embryonic stem cell-derived cardiomyocytes (ESC-CMs) have applications in understanding cardiac disease pathophysiology, pharmacology, and toxicology. Comprehensive characterization of their basic physiological and pharmacological properties is critical in determining the suitability of ESC-CMs as models of cardiac activity. In this study we use video microscopy and quantitative PCR to investigate the responses of mouse ESC-CMs to adrenoceptor, muscarinic, angiotensin II (Ang II), and endothelin-1 (ET-1) receptor activation. Isoprenaline (10 nM-10 μM) increased beating rate and contraction amplitude in all beating bodies (BBs), whereas carbachol (up to 1 μM) and the I(f) channel blocker ZD-7288 (10 μM) decreased contraction frequency. ET-1 (0.01-100 nM) reduced contraction amplitude in all BBs and increased contraction frequency in 50% of BBs; these effects were blocked by the ET(A) receptor antagonist BQ123 (250 nM). Ang II (0.01 nM-1 μM) increased both contraction amplitude (all BBs) and frequency (in 50% of BBs), effects blocked, respectively, by losartan (100 nM) and PD123,319 (200 nM). These results indicate the presence of functional ET(A) and both AT₁ and AT₂ receptors in murine ESC-CMs, but their expression and or activity appears to be evident only in a limited set of BBs.

Endothelin

Endothelin-1 is the most potent vasoconstrictor agent currently identified, and it was originally isolated and characterized from the culture media of aortic endothelial cells. Two other isoforms, termed endothelin-2 and endothelin-3, were subsequently identified, along with structural homologues isolated from the venom of Actractapis engaddensis known as the sarafotoxins. In this review, we will discuss the basic science of endothelins, endothelin-converting enzymes, and endothelin receptors. Only concise background information pertinent to clinical physician is provided. Next we will describe the pathophysiological roles of endothelin-1 in pulmonary arterial hypertension, heart failure, systemic hypertension, and female malignancies, with emphasis on ovarian cancer. The potential intervention with pharmacological therapeutics will be succinctly summarized to highlight the exciting pre-clinical and clinical studies within the endothelin field. Of note is the rapid development of selective endothelin receptor antagonists, which has led to an explosion of research in the field.

At the heart of tissue: endothelin system and end-organ damage

ET (endothelin)-1 was first described as a potent vasoconstrictor. Since then, many other deleterious properties mediated via its two receptors, ETA and ETB, have been described, such as inflammation, fibrosis and hyperplasia. These effects, combined with a wide tissue distribution of the ET system, its up-regulation in pathological situations and a local autocrine/paracrine activity due to a high tissue receptor binding, make the tissue ET system a key local player in end-organ damage. Furthermore, ET-1 interacts in tissues with other systems such as the RAAS (renin-angiotensin-aldosterone system) to exert its effects. In numerous genetically modified animal models, non-specific or organ-targeted ET-1 overexpression causes intense organ damage, especially hypertrophy and fibrosis, in the absence of haemodynamic changes, confirming a local activity of the ET system. ET receptor antagonists have been shown to prevent and sometimes reverse these tissue alterations in an organ-specific manner, leading to long-term benefits and an improvement in survival in different animal models. Potential for such benefits going beyond a pure haemodynamic effect have also been suggested by clinical trial results in which ET receptor antagonism decreased the occurrence of new digital ulcers in patients with systemic sclerosis and delayed the time to clinical worsening in patients with PAH (pulmonary arterial hypertension). The tissue ET system allows therapeutic interventions to provide organ selectivity and beneficial effects in diseases associated with tissue inflammation, hypertrophy or fibrosis.

Genetic polymorphisms in endothelin-receptor-subtype-a-gene as susceptibility factor for obstructive sleep apnea syndrome

INTRODUCTION

Traits of obstructive sleep apnea syndrome (OSAS) such as impaired ventilatory control, craniofacial abnormalities, and concomitant cardiovascular diseases are associated with modified endothelin-1 gene (EDN-1) or endothelin-receptor-subtype-a (EDNRA) gene. The endothelin system regulates the cardiovascular homeostasis. EDN-1 interacts mainly with EDNRA for signal transduction. In our study we investigate associations of EDNRA-polymorphisms (four frequent polymorphisms with an allele frequency >5%) and OSAS severity.

METHODS

Three hundred ninety-three patients older than 18years, of Caucasian origin and with OSAS (AHI>5/h and daytime sleepiness) were investigated by cardiorespiratory polysomnography. In addition 58 control subjects with healthy sleep were recruited from nearly 300 volunteers. We analysed the EDNRA-polymorphisms E335E, H323H, G-231A and G+70C by polymerase-chain-reaction, restriction-fragment-length-polymorphism and real-time-PCR.

RESULTS

Carrier of the mutant G-231A allele had a significantly lower AHI (p=0.03, OR 0.53, 95% CI 0.3-0.94) when comparing patients and controls. When comparing OSAS severity groups without controls we could not detect significant correlations for the four investigated EDNRA-polymorphisms. Our data confirm that BMI (p<0.001) and male gender (p=0.02) are significantly associated with AHI. The allele frequencies were similar.

DISCUSSION

The genetic investigation of OSA remains important. Our control group was relatively small and we investigated 4 reasonable candidates out of more than 100 EDNRA-polymorphisms. The detected protective effect of the mutant G-231A allele needs further confirmation. Gene based research in OSAS should use genome wide scan and should still consider the endothelin system.

Current concepts of neurohormonal activation in heart failure: mediators and mechanisms

Neurohormonal activation is a commonly cited array of phenomena in the body's physiologic response to heart failure. Although various neurohormones and pharmacologic agents that moderate their pathophysiologic effects have been reviewed in the nursing literature, both the mechanisms of neurohormonal system activation and cellular and organ system effects have been described only in brief. Accordingly, this article reviews mechanisms of neurohormonal activation and describes cellular and cardiovascular effects of the (1) sympathetic nervous system, (2) renin-angiotensin-aldosterone system, (3) kallikrein-kininogen-kinin system, (4) vasopressinergic system, (5) natriuretic peptide systems, and (6) endothelin in the context of heart failure. This article implicitly details the physiologic basis for numerous current and potential future pharmacologic agents used in the management of heart failure. It is intended that this article be used as a reference for advanced clinical nursing practice, research, and education.

Contractile regulation by overexpressed ETArequires intact T tubules in adult rat ventricular myocytes

Endothelin (ET)-1 regulates the contractility and growth of the heart by binding G protein-coupled receptors of the ET type A receptor (ETA)/ET type B (ETB) receptor family. ETA, the predominant ET-1 receptor subtype in myocardium, is thought to localize preferentially within cardiac T tubules, but the consequences of mislocalization are not fully understood. Here we examined the effects of the overexpression of ETAin conjunction with T-tubule loss in cultured adult rat ventricular myocytes. In adult myocytes cultured for 3 to 4 days, the normally robust positive inotropic effect (PIE) of ET-1 was lost in parallel with T-tubule degeneration and a decline in ETAprotein levels. In these T tubule-compromised myocytes, an overexpression of ETAusing an adenoviral vector did not rescue the responsiveness to ET-1, despite the robust expression in the surface sarcolemma. The inclusion of the actin polymerization inhibitor cytochalasin D (CD) during culture prevented gross morphological changes including a loss of T tubules and a rounding of intercalated discs, but CD alone did not rescue the responsiveness to ET-1 or prevent ETAdownregulation. The rescue of a normal PIE in 3- to 4-day cultured myocytes required both an increased expression of ETAand intact T tubules (preserved with CD). Therefore, the activation of ETAlocalized in T tubules was associated with a strong PIE, whereas the activation of ETAin surface sarcolemma was not. The results provide insight into the pathological cardiac conditions in which ETAis upregulated and T-tubule morphology is altered.

G-protein coupled receptor signaling in myocardium: not for the faint of heart

Catecholamines, endothelin-1 and angiotensin II are among a diverse group of diffusible extracellular signals that regulate pump function of the heart by binding to G-protein coupled receptors (GPCR). When the body demands a temporary boost of power output or if temporary budgeting of resources is required, these signals can adjust heart rate and contractile strength to maintain continuous perfusion of all vascular beds with nutrient- and oxygen-rich blood. Given adequate time in the face of prolonged challenges, activation of GPCRs can also promote "remodeling of the heart" by increasing cell size, organ size, and chamber dimensions, or by varying tissue composition and altering the expression of protein isoforms controlling excitability and contractility. A common feature of heart disease is the state of chronic activation of GPCR signaling systems. Paradoxically, whereas acute activation is beneficial, chronic activation often contributes to further deterioration of cardiac performance. A better understanding of how chronic GPCR activation contributes to the development of heart disease is needed so that it can be translated into better prevention and therapeutic strategies in the clinic.

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Cardiac GPCRs: GPCR signaling in healthy and failing hearts

G protein-coupled receptors (GPCRs) are widely implicated in human heart disease, making them an important target for cardiac drug therapy. The most commonly studied and clinically targeted cardiac GPCRs include the adrenergic, angiotensin, endothelin, and adenosine receptors. Treatment options focusing on the complex and integrated signaling pathways of these GPCRs are critical for the understanding and amelioration of heart disease. The focus of this review is to highlight the most commonly studied and clinically targeted cardiac GPCRs, placing emphasis on their common signaling components implicated in cardiac disease.

Contractile effects of angiotensin and endothelin in failing and non-failing human hearts

BACKGROUND

Angiotensin II (Ang II) and endothelin-1 (ET-1) share their effects on growth of myocardial cells but have been shown to elicit different effects on myocardial function. However, these effects vary markedly among species, cardiac regions (atrium or ventricle) and failing or non-failing myocardium. We therefore investigated the effects of both peptides on contractile function of isolated human myocytes from failing and non-failing hearts.

METHODS AND RESULTS

Cardiomyocytes were enzymatically isolated and electrically stimulated (15 V, 0.2 Hz). Ang II elicited a positive inotropic effect (PIE) mediated by activation of protein kinase C (PKC) in atrial but no effect in ventricular myocytes. ET-1 (10(-8) M) increased cell-shortening by 146+/-9.3% (p<0.05) in atrial myocytes, by 99.1+/-16.5% (p<0.05) in non-failing ventricular but only by 40.5+/-6.4% (p<0.05) in failing ventricular myocytes. The PIE of ET-1 in failing myocytes was more pronounced at low extracellular pH (+112.6+/-27% at pH 7.0 vs. +40.5+/-6.4% at pH 7.4, p<0.05). Amiloride, a sodium-hydrogen-exchange inhibitor, inhibited two thirds of the PIE of ET-1 in failing myocytes. The PKC-inhibitor decreased the PIE by 50% from 113% to 64% in ventricular myocytes under acidotic conditions.

CONCLUSION

Ang II and ET-1 elicited PIE in atrial myocytes, whereas in ventricular myocytes Ang II did not induce PIE in contrast to ET-1. The PIE of ET-1 was markedly attenuated in failing myocytes. Under acidotic conditions, the PIE of ET-1 was more pronounced in failing myocytes, indicating that ET-1 may activate signaling processes in failing myocytes, which are not activated in normal myocytes.

ET-1 Lys198Asn and ETA Receptor H323H Polymorphisms in Heart Failure

BACKGROUND

The endothelin (ET) system plays a central role in the control of myocardial function and its pathophysiology. The aim of the present study was to explore whether genetic variations of ET-1 (G/T substitution that predicts an Lys/Asn change at codon 198) and its receptor ET(A) (T/C in exon 6, H323H) could predispose carriers to heart failure (HF).

METHODS

Genotyping at these two loci was done in 122 patients with HF [echocardiographic left ventricular ejection fraction (LVEF) < or =40%] and 216 age-matched subjects without HF. Causes of HF included ischemic (n = 96) and idiopathic cardiomyopathies (n = 26).

RESULTS

The ET-1 Lys198Asn was significantly associated with the occurrence of HF (p = 0.005). The risk of HF was independently increased among Asn/Asn in comparison to Lys carriers (OR = 3.2, p = 0.03). Moreover, homozygous carriers of both ET-1 and ET(A) variants showed a marked increase in the risk of HF (adjusted OR = 8.6, p = 0.005), displayed significantly lower LVEF (p = 0.002) and higher left ventricular end-diastolic (p = 0.03) and end-systolic diameters (p = 0.04; for Asn/Asn and TT vs. Lys and C carriers of the ET-1 and ET(A )polymorphisms, respectively). Furthermore, the extent of coronary artery disease (r = -0.62, p < 0.0001) and the Asn/Asn and TT double genotype (r = -0.30, p = 0.0001) were the only significant and independent predictors of LVEF by multivariate analysis.

CONCLUSIONS

The ET-1 Lys198Asn and ET(A) receptor H323H polymorphisms seem to act synergistically to increase the risk of HF.

Cardiovascular endothelins: essential regulators of cardiovascular homeostasis

The endothelin (ET) system consists of 3 ET isopeptides, several isoforms of activating peptidases, and 2 G-protein-coupled receptors, ETA and ETB, that are linked to multiple signaling pathways. In the cardiovascular system, the components of the ET family are expressed in several tissues, notably the vascular endothelium, smooth muscle cells, and cardiomyocytes. There is general agreement that ETs play important physiological roles in the regulation of normal cardiovascular function, and excessive generation of ET isopeptides has been linked to major cardiovascular pathologies, including hypertension and heart failure. However, several recent clinical trials with ET receptor antagonists were disappointing. In the present review, the authors take the stance that ETs are mainly and foremost essential regulators of cardiovascular function, hence that antagonizing normal ET actions, even in patients, will potentially do more harm than good. To support this notion, we describe the predominant roles of ETs in blood vessels, which are (indirect) vasodilatation and ET clearance from plasma and interstitial spaces, against the background of the subcellular mechanisms mediating these effects. Furthermore, important roles of ETs in regulating and adapting heart functions to different needs are addressed, including recent progress in understanding the effects of ETs on diastolic function, adaptations to changes in preload, and the interactions between endocardial-derived ET-1 and myocardial pump function. Finally, the potential dangers (and gains) resulting from the suppression of excessive generation or activity of ETs occurring in some cardiovascular pathological states, such as hypertension, myocardial ischemia, and heart failure, are discussed.

The endothelin system and its role in acute myocardial infarction

Endothelin (ET)-1 is a potent coronary vasoconstrictor. On the heart, ET-1 is a potent positive inotrope and may be pro-arrhythmic. Plasma ET-1 levels are raised after acute myocardial infarction (AMI) and recanalisation in humans. This probably contributes to the coronary vasoconstriction that underlies the myocardial ischaemia and ventricular dysfunction at this time. During occlusion of the rat coronary artery, ventricular arrhythmias are reduced by ET(A) receptor blockade. Short-term ET(A) receptor blockade also reduces infarct size in animal models of AMI (coronary occlusion followed by reperfusion). Blockade of the endothelin-converting enzyme with SM-19712 reduced the infarct size in the rabbit model of AMI. ET(A) receptor blockade is associated with coronary artery dilation in humans. As there are indications that ET(A) receptor antagonists are protective in animal models of AMI, short-term ET(A) receptor blockade should be considered for trial in human AMI.

The role of endothelin-1 in myocarditis and inflammatory cardiomyopathy: old lessons and new insights

Endothelin-1 has emerged as an important participant in the pathophysiology of a variety of cardiovascular diseases, where it may act on endocrine, paracrine and autocrine bases. Here we review its regulated biosynthesis, receptor-mediated signaling, and functional consequences in the heart, with particular emphasis on cardiac development and disease. Exploring published data employing molecular genetic mouse models of endothelin dysregulation, we highlight its heretofore underappreciated role as a pro-inflammatory cytokine. We also present novel micro-array data from one such mouse model, which implicate the specific downstream pathways that may mediate endothelin-1's effects.Key words: endothelin-1, cardiac development, inflammation, transgenic mice, gene expression profiling.

Endothelin receptor antagonists in heart failure: current status and future directions

Experimental evidence suggests that endothelin substantially contributes to left ventricular remodelling and progression of heart failure. Plasma endothelin (ET)-1 levels are increased in patients with heart failure, independent of the aetiology, and correlate with the severity of the disease. Furthermore, tissue endothelin levels and endothelin receptors are upregulated in myocardium from animals and humans with heart failure. In several experimental models of left ventricular remodelling and/or heart failure, treatment with nonselective ET-A and -B as well as selective ET-A antagonists exerted beneficial cardiovascular effects. In patients with heart failure, short-term studies of treatment with endothelin antagonists demonstrated an improvement of haemodynamic parameters; however, long-term treatment with these drugs did not significantly improve combined morbidity/mortality endpoints. Furthermore, in the recently completed Endothelin-A Receptor Antagonist Trial in Heart Failure (EARTH) trial in patients with chronic heart failure, the selective ET-A receptor antagonist darusentan did not significantly affect left ventricular remodelling as assessed by cardiac magnetic resonance imaging. Potential reasons for the lack of beneficial effects of long-term treatment with ET antagonists in patients with heart failure include the following. Firstly, adverse effects on left ventricular healing have been observed when endothelin antagonist therapy was introduced early after myocardial infarction in rats. Secondly, the role of the ET-B receptor in the pathophysiology of heart failure and remodelling processes has not been clearly defined. Finally, for the detection of improvement in left ventricular remodelling, a study needs to be conducted in patients with recent myocardial infarction and signs of heart failure.

Autonomic receptor systems in the failing and aging human heart: similarities and differences

Changes in autonomic receptor systems (alpha- and beta-adrenoceptors and muscarinic receptors) were compared in the aging and failing human heart. In both settings responsiveness of beta-adrenoceptors and all other receptor systems that evoke their effects via cyclic AMP accumulation was diminished. Muscarinic receptor function, on the other hand, was decreased in the aging, but unchanged in the failing heart; in contrast, G protein-coupled receptor kinase activity was increased in the failing, but unchanged in the aging heart. alpha-Adrenoceptor function was unchanged or slightly decreased in the failing heart. However, nothing is known on alpha-adrenoceptor changes in the aging heart. These results indicate that in the failing human heart all autonomic receptor systems appear to be altered in the direction to attenuate beta-adrenoceptor responses to sympathetic (over)stimulation while in the aging human heart autonomic receptor systems appear to be altered in a direction that protects the heart against too pronounced reduction in beta-adrenoceptor responsiveness.

Sarafotoxin 6c (S6c) Reduces Infarct Size and Preserves mRNA for the ETB Receptor in the Ischemic/Reperfused Myocardium of Anesthetized Rats

The aims of this study were to determine if the ETB receptor agonist, sarafotoxin 6c (S6c) reduces myocardial infarct size following myocardial ischemia and reperfusion and to investigate whether any changes in mRNA for endothelin receptors in the injured myocardium were modified by S6c pretreatment. Hypnorm/Hypnovel anesthetized rats were subjected to occlusion of the left main coronary artery for 30 minutes, followed by 120 minutes reperfusion. Animals were administered a bolus dose of S6c (0.24 nmol kg-1 i.v., n = 10) or saline (n = 15) 5 minutes prior to occlusion. At the end of reperfusion, hearts were stained with Evan's Blue dye to delineate area at risk. A 1.5- to 2.0-mm thick slice was cut transmurally 1 mm below the site of ligation for assessment of infarct size by triphenyltetrazolium chloride. A further transmural slice (2.5-3-mm thick) was cut for assessment of receptor mRNA levels by RTPCR. Administration of S6c caused a transient fall in mean arterial blood pressure (MABP) prior to occlusion and attenuated the fall in MABP induced by coronary occlusion. S6c significantly reduced infarct size (13 +/- 4% of area of slice at risk) compared with control hearts (35 +/- 5%; P < 0.05). In control hearts, there was a marked reduction in mRNA content for both ETA (50% reduction) and ETB (70% reduction) receptors in the ischemic zone, compared with non-ischemic tissue. In hearts pre-treated with S6c there was a reduction in ETA, but not ETB receptor mRNA in the ischemic zone. This study has shown that S6c reduces myocardial infarct size and results in preservation of ETB receptor mRNA in ischemic/reperfused tissue.

Binding by serum IgA antibodies from patients with coeliac disease to monkey heart tissue

BACKGROUND

The recently reported increased prevalence of coeliac disease in heart transplant candidates and in patients with autoimmune myocarditis may suggest an autoimmune process towards antigenic components of both myocardium and small bowel. The objective of this study was to determine the possible presence of IgA antibodies directed against heart tissue in sera from patients with coeliac disease.

METHODS

Sera samples from 28 biopsy-proven coeliac disease patients and 81 controls (both healthy and diseased) were assessed by indirect immunofluorescence, with fluorescein isothiocyanate labelled rabbit anti-human IgA, on commercial monkey cardiac muscle sections.

RESULTS

A strong fluorescence around heart muscle fibres was found in 13 out of 15 untreated patients but none in either those treated for coeliac disease or in controls. Pretreatment with tissue transglutaminase, a prominent coeliac auto-antigen, abolished the typical fluorescent pattern almost completely.

CONCLUSIONS

Our study demonstrates that in untreated coeliac disease there is a reaction of IgA antibodies sera, yielding a strong fluorescence, with monkey heart structures, and that tissue transglutaminase is the target antigen in this reaction.

Early activation of cardiac and renal endothelin systems in experimental heart failure

We investigated the time course of the expression of cardiac and renal endothelin systems in tachycardia-induced heart failure in dogs. Eleven beagles underwent rapid pacing at a progressively increased rate over a period of 5 wk, with a weekly clinical examination, echocardiography, measurement of circulating and urinary endothelin-1 (ET-1), and myocardial and renal tissue biopsies. Real-time quantitative PCR was used for determinations of tissue prepro-ET-1 (ppET-1), ET-1-converting enzyme (ECE-1), and ETA and ETB receptor mRNA. Cardiac and renal tissue ET-1 contents were evaluated by immunostaining and measured by radioimmunoassay at autopsy. Rapid pacing caused a progressive increase in end-systolic and end-diastolic ventricular volumes (P < 0.05) from week 2 together with a decrease in ejection fraction and in mean velocity of circumferential shortening (P < 0.05) from week 1. These changes were tightly correlated to myocardial ppET-1 and renal ETA receptor mRNA and less so to myocardial ECE-1 mRNA, and they occurred before any increase in plasma and urinary ET-1 (P < 0.05 from week 4) and clinical signs of heart failure. Renal ppET-1 did not change. Both cardiac and renal ET-1 peptide contents were increased at autopsy. We conclude that tachycardia-induced heart failure in dogs is characterized by an early activation of the cardiac and renal tissue endothelin systems, which occurs before any changes in circulating and urinary ET-1 and is closely related to altered ventricular function.

The endothelin system and its role in acute myocardial infarction

Immediately after an acute myocardial infarction (AMI) or in models of ischemia-reperfusion injury, cardiac endothelin (ET) system is markedly activated, and plasma levels of ET are increased. In the heart, expression of the main components of the ET system (ET-1 peptide, both receptor subtypes ETA and ETB, though not endothelin converting enzyme) are increased both at the gene level and protein level, in the viable myocardium, and--even more substantially--in the necrotic area. Despite these conspicuous abnormalities, the role of ET in this setting remains unclear. In the absence of human data, most short-term studies in animals (in terms of hours to up to 8 days post-AMI) and in the reperfused ischemic heart, have found beneficial effects of ET receptor blockade on survival rate, incidence of arrhythmias, cardiac function, and morphology. In contrast, many studies in which a long-term ET inhibition was started immediately post-infarction and the late effects were examined in animals with ensuing chronic heart failure (14-100 days postinfarction), adverse effects were also observed, such as scar thinning, further ventricular dilation, or even a worse survival rate. It appears that the ET system plays a dual role during the early post-AMI period. At present, it is not clear whether the short-term beneficial effects or long-term adverse effects of ET receptor blockade would prevail. Acute use of short-acting ET receptor antagonists in patients with AMI complicated by an acute heart failure is an attractive possibility that also remains to be investigated.

Tezosentan in patients with acute heart failure and acute coronary syndromes: results of the Randomized Intravenous TeZosentan Study (RITZ-4)

OBJECTIVES

We sought to determine the effect of tezosentan in patients with acute decompensated heart failure (HF) associated with acute coronary syndrome (ACS).

BACKGROUND

Tezosentan is a dual endothelin receptor antagonist that has been shown to improve cardiac output, decrease pulmonary capillary wedge pressure, and reduce pulmonary and systemic vascular resistance in initial clinical studies in acute decompensated HF.

METHODS

The Randomized Intravenous TeZosentan (RITZ)-4 study was a multicenter, randomized, double-blinded, placebo-controlled study of tezosentan in patients with acute decompensated HF associated with ACS. A total of 193 patients were randomized to receive tezosentan (25 mg/h for 1 h, then 50 mg/h for 23 to 47 h) or placebo. Patients with evidence of acute decompensated HF and ACS were eligible to participate. The primary end point was the composite of death, worsening HF, recurrent ischemia, and recurrent or new myocardial infarction within 72 h.

RESULTS

No significant differences were observed between placebo and 50 mg/h tezosentan in the composite primary end point: 24.2% (95% confidence interval [CI] 16.0% to 34.1%) and 28.9% (95% CI 20.1% to 39.0%), respectively (p = 0.5152). Symptomatic hypotension was more frequent in the treatment group.

CONCLUSIONS

At the doses studied, tezosentan did not result in a significant improvement in the composite primary clinical end point in the RITZ-4 trial. Tezosentan did not demonstrate pro-ischemic effects in this population. Symptomatic hypotension may have resulted in an increased number of adverse events in the treatment group. Further studies with lower tezosentan doses are warranted.

Will endothelin receptor antagonists have a role in heart failure?

Mixed ET(A/B) and selective ET(A) receptor antagonists showed promising hemodynamic and symptomatic improvements in patients with heart failure. Randomized, clinical trials to investigate the effects of ET receptor antagonists on survival in patients with heart failure still need to be conducted. Also, the effects of selective ET(A) and mixed ET(A/B) receptor antagonists on the clinical outcome of patients with CHF will have to be assessed.

Cardiac beta-adrenoceptor changes in monocrotaline-treated rats: differences between membrane preparations from whole ventricles and isolated ventricular cardiomyocytes

In monocrotaline (MCT)-treated rats the beta-adrenoceptor-G-protein-adenylyl cyclase system-determined in crude membrane preparations from whole ventricular tissue-was desensitized not only in right (RV) but also in left ventricles (LV). This study aimed to assess the specific contribution of cardiomyocytes to these beta-adrenoceptor changes. Six-week-old male Wistar rats were treated with 60 mg/kg body weight MCT intraperitoneally; within 4-6 weeks, rats developed marked RV hypertrophy. Cardiomyocytes were isolated from RVs and LVs. In RV cardiomyocytes of MCT-treated rats, beta-adrenoceptor density was significantly reduced whereas it was unaltered in LV cardiomyocytes. Reduction of RV cardiomyocyte beta-adrenoceptors was due to a selective beta(1)-adrenoceptor reduction. Isoprenaline (100 microM)-induced cAMP increase was significantly reduced in RV but not in LV cardiomyocytes of MCT-treated rats. G protein-coupled receptor kinase activity was increased in RV but not in LV cardiomyocytes. alpha(1)-Adrenoceptor density and noradrenaline-induced increase in inositol phosphate formation were significantly reduced only in RV but not in LV cardiomyocytes from MCT-treated rats. It is concluded that in cardiomyocytes of MCT-treated rats, cardiac beta-adrenoceptors and alpha -adrenoceptors are chamber-specifically desensitized only in the RV. Thus, changes in cardiac beta-adrenoceptors determined in membrane preparations from whole tissue homogenates do not correctly reflect changes occurring in cardiomyocytes.

Regulators of G-protein signalling: multifunctional proteins with impact on signalling in the cardiovascular system

Regulator of G-protein signalling (RGS) proteins form a superfamily of at least 25 proteins, which are highly diverse in structure, expression patterns, and function. They share a 120 amino acid homology domain (RGS domain), which exhibits GTPase accelerating activity for alpha-subunits of heterotrimeric G-proteins, and thus, are negative regulators of G-protein-mediated signalling. Based on the organisation of the Rgs genes, structural similarities, and differences in functions, they can be divided into at least six subfamilies of RGS proteins and three more families of RGS-like proteins. Many of these proteins regulate signalling processes within cells, not only via interaction with G-protein alpha-subunits, but are G-protein-regulated effectors, Gbetagamma scavenger, or scaffolding proteins in signal transduction complexes as well. The expression of at least 16 different RGS proteins in the mammalian or human myocardium have been described. A subgroup of at least eight was detected in a single atrial myocyte. The exact functions of these proteins remain mostly elusive, but RGS proteins such as RGS4 are involved in the regulation of G(i)-protein betagamma-subunit-gated K(+) channels. An up-regulation of RGS4 expression has been consistently found in human heart failure and some animal models. Evidence is increasing that the enhanced RGS4 expression counter-regulates the G(q/11)-induced signalling caused by hypertrophic stimuli. In the vascular system, RGS5 seems to be an important signalling regulator. It is expressed in vascular endothelial cells, but not in cultured smooth muscle cells. Its down-regulation, both in a model of capillary morphogenesis and in an animal model of stroke, render it a candidate gene, which may be involved in the regulation of capillary growth, angiogenesis, and in the pathophysiology of stroke.

Both endothelin-A and endothelin-B receptors are present on adult rat cardiac ventricular myocytes

Endothelin-A (ET(A)) and endothelin-B (ET(B)) receptors have been demonstrated in intact heart and cardiac membranes. ET(A) receptors have been demonstrated on adult ventricular myocytes. The aim of the present study was to determine the presence of ET(B) and the relative contribution of this receptor subtype to total endothelin-1 (ET-1) binding on adult ventricular myocytes. Saturation binding experiments indicated that ET-1 bound to a single population of receptors (Kd = 0.52 +/- 0.13 nM, n = 4) with an apparent maximum binding (Bmax) of 2.10 +/- 0.25 sites (x 10(5))/cell (n = 4). Competition experiments using 40 pM [125I]ET-1 and nonradioactive ET-1 revealed a Ki of 660 +/- 71 pM (n = 10) and a Hill coefficient (nH) of 0.99 +/- 0.10 (n = 10). A selective ET(A) antagonist, BQ610, displaced 80% of the bound [125I]ET-1. No displacement was observed by concentrations of an ET(B)-selective antagonist, BQ788, up to 1.0 microM. However, in the presence of 1.0 microM BQ610, BQ788 inhibited the remaining [125I]ET-1 binding. Similarly, in the presence of 1.0 microM BQ788, BQ610 inhibited the remaining specific [125I]ET-1 binding. Binding of an ET(B1)-selective agonist, [125I]IRL-1620, confirmed the presence of ET(B). ET(B) bound to ET-1 irreversibly, whereas binding to ET(A) demonstrated both reversible and irreversible components, and BQ610 and BQ788 bound reversibly. Reducing the incubation temperature to 0 degrees C did not alter the irreversible component of ET-1 binding. Hence, both ET(A) and ET(B) receptors are present on intact adult rat ventricular myocytes, and the ratio of ET(A):ET(B) binding sites is 4:1. Both receptor subtypes bind to ET-1 by a two-step association involving the formation of a tight receptor-ligand complex; however, the kinetics of ET-1 binding to ET(A) versus ET(B) differ.

Angiotensin-converting enzyme inhibitor therapy prevents upregulation of endothelin-converting enzyme-1 in failing human myocardium

In this study, we investigated the role of the renin-angiotensin system in expression of the endothelin system in atrial myocardium of patients with congestive heart failure. Atrial myocardium of control patients without angiotensin-converting enzyme (ACE) inhibitor therapy and heart failure patients without or with ACE inhibitor therapy undergoing aorto-coronary bypass surgery was studied. Endothelin-converting enzyme-1 (ECE-1) expression and endothelin-1 peptide level was upregulated in myocardium of heart failure patients without ACE inhibition. ACE inhibitor therapy prevented upregulation of ECE-1 and endothelin-1 in failing myocardium. Prepro-endothelin-1 and endothelin receptor A expression were not affected by heart failure. Endothelin receptor B was downregulated in heart failure patients. Our data demonstrate an upregulation of ECE-1 mRNA expression in failing human myocardium. Inhibition of the renin-angiotensin system by ACE inhibitor treatment prevents upregulation of ECE-1, suggesting that angiotensin II regulates ECE-1 expression in vivo.

Altered expression of endothelin receptors in failing human left ventricles

BACKGROUND

Endothelin signaling is activated in failing human hearts, and may contribute to progressive myocardial dysfunction and remodeling. However, the behavior of endothelin receptor systems (ET(A) and ET(B)) in failing human hearts is not well understood.

METHODS AND RESULTS

(125)[I]-endothelin-1 binding assays conducted in the presence of a non-hydrolyzable guanine nucleotide to uncouple agonist binding demonstrated that membranes prepared from nonfailing left ventricles (LVs) exhibit a mixed pattern of ET(A) ( approximately 60%) and ET(B) ( approximately 40%) receptor protein expression. Chronic LV failure from either idiopathic dilated (IDC) or ischemic (ISC) cardiomyopathy was accompanied by a significant (P<0.001) increase in ET(A) receptor density, to approximately 80% of the total population, and a significant (P<0.02) decrease in ET(B) receptor density. Ribonuclease protection assays demonstrated an increase in ET(A) mRNA abundance in IDC and ISC LVs, and a significant (P<0.04) increase in ET(B) mRNA abundance in ISC LVs. Enzyme-linked immunoabsorbent assays demonstrated a significant increase in tissue immunoreactive endothelin-1 concentration in IDC (P=0.01) and in IDC+ISC LVs (P=0.02), but receptor subtype protein or mRNA level was not significantly correlated with tissue ET-1 across all LVs. In situ reverse-transcription polymerase chain reaction in LV sections demonstrated that in both failing and nonfailing LVs the ET(A) gene is expressed in cardiac myocytes, vascular smooth muscle and endothelium; the ET(B) gene is expressed in cardiac myocytes, fibroblasts and endothelium; and the prepro-endothelin-1 gene is expressed in myocytes and interstitial cells.

CONCLUSIONS

In chronically failing human LVs, ET(A) receptor density is increased to become the dominant subtype while ET(B) receptor density is decreased. The ET(A), but not the ET(B) density change is accompanied by cognate regulation of mRNA abundance. Both receptor genes and prepro-endothelin-1 are expressed in cardiac myocytes. Finally, based on a lack of correlation with endothelin-1 tissue levels, it is unlikely that the failure-related changes in ET(A) and ET(B) receptor protein and mRNA expression result from homologous regulation by agonist exposure.

Genetic polymorphisms and oxidative stress in heart failure

Heart failure results from various known cardiovascular diseases, such as coronary artery disease, or can be the result of an idiopathic dilated cardiomyopathy. It is of utmost importance for diagnostic, preventive, and therapeutic purposes to understand the cellular events that trigger the cascade of functional and structural changes that result in the development and progression of heart failure. Progress in unraveling the genetic background in both ischemic and nonischemic cardiomyopathies has been slow compared with that for monogenic diseases, such as some forms of hypertrophic cardiomyopathy or familial dilated cardiomyopathies. It is likely that susceptibility to and risk of progression of heart failure are both influenced by many genes acting in concert or independently. Among the diverse subcellular mechanisms implicated in the pathogenesis and progression of heart failure, reactive oxygen species play a major role. The search for genetic polymorphisms in clinical association studies in order to identify genotypes susceptible to develop and affect the progression to heart failure has been the focus of many investigations over the past several years. In this review, the authors summarize the current data in support of the role of various polymorphisms of genes related to oxidative stress in the susceptibility to develop heart failure, and its progression.