Myocardial contractile function and heart rate in mice with myocyte-specific overexpression of endothelial nitric oxide synthase

Role of Ca2+ in healthy and pathologic cardiac function: from normal excitation-contraction coupling to mutations that cause inherited arrhythmia

Calcium (Ca²⁺) ions are a key second messenger involved in the rhythmic excitation and contraction of cardiomyocytes throughout the heart. Proper function of Ca²⁺-handling proteins is required for healthy cardiac function, whereas disruption in any of these can cause cardiac arrhythmias. This comprehensive review provides a broad overview of the roles of Ca²⁺-handling proteins and their regulators in healthy cardiac function and the mechanisms by which mutations in these proteins contribute to inherited arrhythmias. Major Ca²⁺ channels and Ca²⁺-sensitive regulatory proteins involved in cardiac excitation-contraction coupling are discussed, with special emphasis on the function of the RyR2 macromolecular complex. Inherited arrhythmia disorders including catecholaminergic polymorphic ventricular tachycardia, long QT syndrome, Brugada syndrome, short QT syndrome, and arrhythmogenic right-ventricular cardiomyopathy are discussed with particular emphasis on subtypes caused by mutations in Ca²⁺-handling proteins.

Adenosine kinase (ADK) inhibition with ABT-702 induces ADK protein degradation and a distinct form of sustained cardioprotection

Pharmacological inhibition of adenosine kinase (ADK), the major route of myocardial adenosine metabolism, can elicit acute cardioprotection against ischemia-reperfusion (IR) by increasing adenosine signaling. Here, we identified a novel, extended effect of the ADK inhibitor, ABT-702, on cardiac ADK protein longevity and investigated its impact on sustained adenosinergic cardioprotection. We found that ABT-702 treatment significantly reduced cardiac ADK protein content in mice 24-72 h after administration (IP or oral). ABT-702 did not alter ADK mRNA levels, but strongly diminished (ADK-L) isoform protein content through a proteasome-dependent mechanism. Langendorff perfusion experiments revealed that hearts from ABT-702-treated mice maintain higher adenosine release long after ABT-702 tissue elimination, accompanied by increased basal coronary flow (CF) and robust tolerance to IR. Sustained cardioprotection by ABT-702 did not involve increased nitric oxide synthase expression, but was completely dependent upon increased adenosine release in the delayed phase (24 h), as indicated by the loss of cardioprotection and CF increase upon perfusion of adenosine deaminase or adenosine receptor antagonist, 8-phenyltheophylline. Importantly, blocking adenosine receptor activity with theophylline during ABT-702 administration prevented ADK degradation, preserved late cardiac ADK activity, diminished CF increase and abolished delayed cardioprotection, indicating that early adenosine receptor signaling induces late ADK degradation to elicit sustained adenosine release. Together, these results indicate that ABT-702 induces a distinct form of delayed cardioprotection mediated by adenosine receptor-dependent, proteasomal degradation of cardiac ADK and enhanced adenosine signaling in the late phase. These findings suggest ADK protein stability may be pharmacologically targeted to achieve sustained adenosinergic cardioprotection.

Cardiovascular "Patterns" of H2S and SSNO--Mix Evaluated from 35 Rat Hemodynamic Parameters

This work is based on the hypothesis that it is possible to characterize the cardiovascular system just from the detailed shape of the arterial pulse waveform (APW). Since H₂S, NO donor S-nitrosoglutathione (GSNO) and their H₂S/GSNO products (SSNO⁻-mix) have numerous biological actions, we aimed to compare their effects on APW and to find characteristic “patterns” of their actions. The right jugular vein of anesthetized rats was cannulated for i.v. administration of the compounds. The left carotid artery was cannulated to detect APW. From APW, 35 hemodynamic parameters (HPs) were evaluated. H₂S transiently influenced all 35 HPs and from their cross-relationships to systolic blood pressure “patterns” and direct/indirect signaling pathways of the H₂S effect were proposed. The observed “patterns” were mostly different from the published ones for GSNO. Effect of SSNO⁻-mix (≤32 nmol kg⁻¹) on blood pressure in the presence or absence of a nitric oxide synthase inhibitor (L-NAME) was minor in comparison to GSNO, suggesting that the formation of SSNO⁻-mix in blood diminished the hemodynamic effect of NO. The observed time-dependent changes of 35 HPs, their cross-relationships and non-hysteresis/hysteresis profiles may serve as “patterns” for the conditions of a transient decrease/increase of blood pressure caused by H₂S.

Enhanced dimethylarginine degradation improves coronary flow reserve and exercise tolerance in Duchenne muscular dystrophy carrier mice

Duchenne muscular dystrophy (DMD) is an X-linked disease caused by null mutations in dystrophin and characterized by muscle degeneration. Cardiomyopathy is common and often prevalent at similar frequency in female DMD carriers irrespective of whether they manifest skeletal muscle disease. Impaired muscle nitric oxide (NO) production in DMD disrupts muscle blood flow regulation and exaggerates postexercise fatigue. We show that circulating levels of endogenous methylated arginines including asymmetric dimethylarginine (ADMA), which act as NO synthase inhibitors, are elevated by acute necrotic muscle damage and in chronically necrotic dystrophin-deficient mice. We therefore hypothesized that excessive ADMA impairs muscle NO production and diminishes exercise tolerance in DMD. We used transgenic expression of dimethylarginine dimethylaminohydrolase 1 (DDAH), which degrades methylated arginines, to investigate their contribution to exercise-induced fatigue in DMD. Although infusion of exogenous ADMA was sufficient to impair exercise performance in wild-type mice, transgenic DDAH expression did not rescue exercise-induced fatigue in dystrophin-deficient male mdx mice. Surprisingly, DDAH transgene expression did attenuate exercise-induced fatigue in dystrophin-heterozygous female mdx carrier mice. Improved exercise tolerance was associated with reduced heart weight and improved cardiac β-adrenergic responsiveness in DDAH-transgenic mdx carriers. We conclude that DDAH overexpression increases exercise tolerance in female DMD carriers, possibly by limiting cardiac pathology and preserving the heart's responses to changes in physiological demand. Methylated arginine metabolism may be a new target to improve exercise tolerance and cardiac function in DMD carriers or act as an adjuvant to promote NO signaling alongside therapies that partially restore dystrophin expression in patients with DMD.NEW & NOTEWORTHY Duchenne muscular dystrophy (DMD) carriers are at risk for cardiomyopathy. The nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is released from damaged muscle in DMD and impairs exercise performance. Transgenic expression of dimethylarginine dimethylaminohydrolase to degrade ADMA prevents cardiac hypertrophy, improves cardiac function, and improves exercise tolerance in DMD carrier mice. These findings highlight the relevance of ADMA to muscular dystrophy and have important implications for therapies targeting nitric oxide in patients with DMD and DMD carriers.

Plastics and cardiovascular health: phthalates may disrupt heart rate variability and cardiovascular reactivity

Plastics have revolutionized medical device technology, transformed hematological care, and facilitated modern cardiology procedures. Despite these advances, studies have shown that phthalate chemicals migrate out of plastic products and that these chemicals are bioactive. Recent epidemiological and research studies have suggested that phthalate exposure adversely affects cardiovascular function. Our objective was to assess the safety and biocompatibility of phthalate chemicals and resolve the impact on cardiovascular and autonomic physiology. Adult mice were implanted with radiofrequency transmitters to monitor heart rate variability, blood pressure, and autonomic regulation in response to di-2-ethylhexyl-phthalate (DEHP) exposure. DEHP-treated animals displayed a decrease in heart rate variability (-17% SD of normal beat-to-beat intervals and -36% high-frequency power) and an exaggerated mean arterial pressure response to ganglionic blockade (31.5% via chlorisondamine). In response to a conditioned stressor, DEHP-treated animals displayed enhanced cardiovascular reactivity (-56% SD major axis Poincarè plot) and prolonged blood pressure recovery. Alterations in cardiac gene expression of endothelin-1, angiotensin-converting enzyme, and nitric oxide synthase may partly explain these cardiovascular alterations. This is the first study to show an association between phthalate chemicals that are used in medical devices with alterations in autonomic regulation, heart rate variability, and cardiovascular reactivity. Because changes in autonomic balance often precede clinical manifestations of hypertension, atherosclerosis, and conduction abnormalities, future studies are warranted to assess the downstream impact of plastic chemical exposure on end-organ function in sensitive patient populations. This study also highlights the importance of adopting safer biomaterials, chemicals, and/or surface coatings for use in medical devices.NEW & NOTEWORTHY Phthalates are widely used in the manufacturing of consumer and medical products. In the present study, di-2-ethylhexyl-phthalate exposure was associated with alterations in heart rate variability and cardiovascular reactivity. This highlights the importance of investigating the impact of phthalates on health and identifying suitable alternatives for medical device manufacturing.

Thioredoxin Uses a GSH-independent Route to Deglutathionylate Endothelial Nitric-oxide Synthase and Protect against Myocardial Infarction

Reversible glutathionylation plays a critical role in protecting protein function under conditions of oxidative stress generally and for endothelial nitric-oxide synthase (eNOS) specifically. Glutathione-dependent glutaredoxin-mediated deglutathionylation of eNOS has been shown to confer protection in a model of heart damage termed ischemia-reperfusion injury, motivating further study of eNOS deglutathionylation in general. In this report, we present evidence for an alternative mechanism of deglutathionylation. In this pathway thioredoxin (Trx), a small cellular redox protein, is shown to rescue eNOS from glutathionylation during ischemia-reperfusion in a GSH-independent manner. By comparing mice with global overexpression of Trx and mice with cardiomyocyte-specific overexpression of Trx, we demonstrate that vascular Trx-mediated deglutathionylation of eNOS protects against ischemia-reperfusion-mediated myocardial infarction. Trx deficiency in endothelial cells promoted eNOS glutathionylation and reduced its enzymatic activity, whereas increased levels of Trx led to deglutathionylated eNOS. Thioredoxin-mediated deglutathionylation of eNOS in the coronary artery in vivo protected against reperfusion injury, even in the presence of normal levels of GSH. We further show that Trx directly interacts with eNOS, and we confirmed that Cys-691 and Cys-910 are the glutathionylated sites, as mutation of these cysteines partially rescued the decrease in eNOS activity, whereas mutation of a distal site, Cys-384, did not. Collectively, this study shows for the first time that Trx is a potent deglutathionylating protein in vivo and in vitro that can deglutathionylate proteins in the presence of high levels of GSSG in conditions of oxidative stress.

2.1 GHz electromagnetic field does not change contractility and intracellular Ca2+ transients but decreases β-adrenergic responsiveness through nitric oxide signaling in rat ventricular myocytes

PURPOSE

Due to the increasing use of wireless technology in developing countries, particularly mobile phones, the influence of electromagnetic fields (EMF) on biologic systems has become the subject of an intense debate. Therefore, in this study we investigated the effect of 2.1 GHz EMF on contractility and beta-adrenergic (β-AR) responsiveness of ventricular myocytes.

MATERIALS AND METHODS

Rats were randomized to the following groups: Sham rats (SHAM) and rats exposed to 2.1 GHz EMF for 2 h/day for 10 weeks (EM-10). Sarcomere shortening and Ca(2+) transients were recorded in isolated myocytes loaded with Fura2-AM and electrically stimulated at 1 Hz, while L-type Ca(2+) currents (I(CaL)) were measured using whole-cell patch clamping at 36 ± 1°C. Cardiac nitric oxide (NO) levels were measured in tissue samples using a colorimetric assay kit.

RESULTS

Fractional shortening and amplitude of the matched Ca(2+) transients were not changed in EM-10 rats. Although the isoproterenol-induced (10(-6) M) I(CaL) response was reduced in rats exposed to EMF, basal I(CaL) density in myocytes was similar between the two groups (p < 0.01). Moreover, EMF exposure led to a significant increase in nitric oxide levels in rat heart (p < 0.02).

CONCLUSIONS

Long-term exposure to 2.1 GHz EMF decreases β-AR responsiveness of ventricular myocytes through NO signaling.

TRPC3 contributes to regulation of cardiac contractility and arrhythmogenesis by dynamic interaction with NCX1

Aim

TRPC3 is a non-selective cation channel, which forms a Ca²⁺ entry pathway involved in cardiac remodelling. Our aim was to analyse acute electrophysiological and contractile consequences of TRPC3 activation in the heart.

Methods and results

We used a murine model of cardiac TRPC3 overexpression and a novel TRPC3 agonist, GSK1702934A, to uncover (patho)physiological functions of TRPC3. GSK1702934A induced a transient, non-selective conductance and prolonged action potentials in TRPC3-overexpressing myocytes but lacked significant electrophysiological effects in wild-type myocytes. GSK1702934A transiently enhanced contractility and evoked arrhythmias in isolated Langendorff hearts from TRPC3-overexpressing but not wild-type mice. Interestingly, pro-arrhythmic effects outlasted TRPC3 current activation, were prevented by enhanced intracellular Ca²⁺ buffering, and suppressed by the NCX inhibitor 3′,4′-dichlorobenzamil hydrochloride. GSK1702934A substantially promoted NCX currents in TRPC3-overexpressing myocytes. The TRPC3-dependent electrophysiologic, pro-arrhythmic, and inotropic actions of GSK1702934A were mimicked by angiotensin II (AngII). Immunocytochemistry demonstrated colocalization of TRPC3 with NCX1 and disruption of local interaction upon channel activation by either GSK1702934A or AngII.

Conclusion

Cardiac TRPC3 mediates Ca²⁺ and Na⁺ entry in proximity of NCX1, thereby elevating cellular Ca²⁺ levels and contractility. Excessive activation of TRPC3 is associated with transient cellular Ca²⁺ overload, spatial uncoupling between TRPC3 and NCX1, and arrhythmogenesis. We propose TRPC3-NCX micro/nanodomain communication as determinant of cardiac contractility and susceptibility to arrhythmogenic stimuli.

Endothelial nitric oxide synthase single nucleotide polymorphism and left ventricular function in early chronic kidney disease

Background

Chronic kidney disease (CKD) is associated with accelerated cardiovascular disease and heart failure. Endothelial nitric oxide synthase (eNOS) Glu298Asp single nucleotide polymorphism (SNP) genotype has been associated with a worse phenotype amongst patients with established heart failure and in patients with progression of their renal disease. The association of a cardiac functional difference in non-dialysis CKD patients with no known previous heart failure, and eNOS gene variant is investigated.

Methods

140 non-dialysis CKD patients, who had cardiac magnetic resonance (CMR) imaging and tissue doppler echocardiography as part of two clinical trials, were genotyped for eNOS Glu298Asp SNP retrospectively.

Results

The median estimated glomerular filtration rate (eGFR) was 50mls/min and left ventricular ejection fraction (LVEF) was 74% with no overt diastolic dysfunction in this cohort. There were significant differences in LVEF across eNOS genotypes with GG genotype being associated with a worse LVEF compared to other genotypes (LVEF: GG 71%, TG 76%, TT 73%, p = 0.006). After multivariate analysis, (adjusting for age, eGFR, baseline mean arterial pressure, contemporary CMR heart rate, total cholesterol, high sensitive C-reactive protein, body mass index and gender) GG genotype was associated with a worse LVEF, and increased LV end-diastolic and systolic index (p = 0.004, 0.049 and 0.009 respectively).

Conclusions

eNOS Glu298Asp rs1799983 polymorphism in CKD patients is associated with relevant sub-clinical cardiac remodelling as detected by CMR. This gene variant may therefore represent an important genetic biomarker, and possibly highlight pathways for intervention, in these patients who are at particular risk of worsening cardiac disease as their renal dysfunction progresses.

Cardioprotective effects of melatonin against myocardial injuries induced by chronic intermittent hypoxia in rats

Obstructive sleep apnea (OSA) associated with chronic intermittent hypoxia (CIH) increases the morbidity and mortality of ischemic heart disease in patients. Yet, there is a paucity of preventive measures targeting the pathogenesis of CIH-induced myocardial injury. We examined the cardioprotective effect of melatonin against the inflammation, fibrosis and the deteriorated sarcoplasmic reticulum (SR) Ca(2+) homeostasis, and ischemia/reperfusion (I/R)-induced injury exacerbated by CIH. Adult male Sprague Dawley rats that had received a daily injection of melatonin (10 mg/kg) or vehicle were exposed to CIH treatment mimicking a severe OSA condition for 4 wk. Systolic pressure, heart weights, and malondialdehyde were significantly increased in hypoxic rats but not in the melatonin-treated group, when compared with the normoxic control. Levels of the expression of inflammatory cytokines (TNF-α, IL-6, and COX-2) and fibrotic markers (PC1 and TGF-β) were significantly elevated in the hypoxic group but were normalized by melatonin. Additionally, infarct size of isolated hearts with regional I/R was substantial in the hypoxic group treated with vehicle but not in the melatonin-treated group. Moreover, melatonin treatment mitigated the SR-Ca(2+) homeostasis in the cardiomyocyte during I/R with (i) Ca(2+) overloading, (ii) decreased SR-Ca(2+) content, (iii) lowered expression and activity of Ca(2+) -handling proteins (SERCA2a and NCX1),and (iv) decreased expressions of CAMKII and phosphorylated eNOS(ser1177). Furthermore, melatonin ameliorated the level of expression of antioxidant enzymes (CAT and MnSOD) and NADPH oxidase (p22 and NOX2). Results support a prophylactic usage of melatonin in OSA patients, which protects against CIH-induced myocardial inflammation and fibrosis with impaired SR-Ca(2+) handling and exacerbated I/R injury.

Endothelial dysfunction in adipose triglyceride lipase deficiency

Systemic knockout of adipose triglyceride lipase (ATGL), the pivotal enzyme of triglyceride lipolysis, results in a murine phenotype that is characterized by progredient cardiac steatosis and severe heart failure. Since cardiac and vascular dysfunction have been closely related in numerous studies we investigated endothelium-dependent and -independent vessel function of ATGL knockout mice. Aortic relaxation studies and Langendorff perfusion experiments of isolated hearts showed that ATGL knockout mice suffer from pronounced micro- and macrovascular endothelial dysfunction. Experiments with agonists directly targeting vascular smooth muscle cells revealed the functional integrity of the smooth muscle cell layer. Loss of vascular reactivity was restored ~50% upon treatment of ATGL knockout mice with the PPARα agonist Wy14,643, indicating that this phenomenon is partly a consequence of impaired cardiac contractility. Biochemical analysis revealed that aortic endothelial NO synthase expression and activity were significantly reduced in ATGL deficiency. Enzyme activity was fully restored in ATGL mice treated with the PPARα agonist. Biochemical analysis of perivascular adipose tissue demonstrated that ATGL knockout mice suffer from perivascular inflammatory oxidative stress which occurs independent of cardiac dysfunction and might contribute to vascular defects. Our results reveal a hitherto unrecognized link between disturbed lipid metabolism, obesity and cardiovascular disease.

Targeting NOS as a therapeutic approach for heart failure

Nitric oxide is a key signaling molecule in the heart and is produced endogenously by three isoforms of nitric oxide synthase, neuronal NOS (NOS1), endothelial NOS (NOS3), and inducible NOS (NOS2). Nitric oxide signals via cGMP-dependent or independent pathways to modulate downstream proteins via specific post translational modifications (i.e. cGMP-dependent protein kinase phosphorylation, S-nitrosylation, etc.). Dysfunction of NOS (i.e. altered expression, location, coupling, activity, etc.) exists in various cardiac disease conditions, such as heart failure, contributing to the contractile dysfunction, adverse remodeling, and hypertrophy. This review will focus on the signaling pathways of each NOS isoform during health and disease, and discuss current and potential therapeutic approaches targeting nitric oxide signaling to treat heart disease.

Pathophysiology of hypertension in the absence of nitric oxide/cyclic GMP signaling

The nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling system is a well-characterized modulator of cardiovascular function, in general, and blood pressure, in particular. The availability of mice mutant for key enzymes in the NO-cGMP signaling system facilitated the identification of interactions with other blood pressure modifying pathways (e.g. the renin-angiotensin-aldosterone system) and of gender-specific effects of impaired NO-cGMP signaling. In addition, recent genome-wide association studies identified blood pressure-modifying genetic variants in genes that modulate NO and cGMP levels. Together, these findings have advanced our understanding of how NO-cGMP signaling regulates blood pressure. In this review, we will summarize the results obtained in mice with disrupted NO-cGMP signaling and highlight the relevance of this pathway as a potential therapeutic target for the treatment of hypertension.

Nitric oxide synthases and heart failure - lessons from genetically manipulated mice

Nitric oxide (NO) is synthesized by three distinct NO synthase (NOS) isoforms (neuronal, inducible, and endothelial NOS), all of which are expressed in the human heart. The roles of NOSs in the pathogenesis of heart failure have been described in pharmacological studies with NOS inhibitors. Recently, genetically engineered animals have been used. We have generated mice in which all 3 NOS isoforms are completely disrupted (triple n/i/eNOS(-/-) mice). Morphological, echocardiographic, and hemodynamic analysis were performed in wild-type, singly nNOS(-/-), iNOS(-/-), eNOS(-/-), and triple n/i/eNOS(-/-) mice. Importantly, significant left ventricular (LV) hypertrophy and diastolic dysfunction was noted only in n/i/eNOS(-/-) mice, and those pathology was similar to diastolic heart failure in humans. Finally, treatment with an angiotensin II type 1 (AT1) receptor blocker, significantly prevented those abnormalities. These results provide the evidence that AT1 receptor pathway plays a center role in the pathogenesis of cardiac disorders in the n/i/eNOS(-/-) mice. Our studies with triple n/i/eNOS(-/-) mice provide pivotal insights into an understanding of the pathophysiology of NOSs in human heart failure.

Endothelial NOS (NOS3) impairs myocardial function in developing sepsis

Endothelial nitric oxide synthase (NOS)3-derived nitric oxide (NO) modulates inotropic response and diastolic interval for optimal cardiac performance under non-inflammatory conditions. In sepsis, excessive NO production plays a key role in severe hypotension and myocardial dysfunction. We aimed to determine the role of NOS3 on myocardial performance, NO production, and time course of sepsis development. NOS3(-/-) and C57BL/6 wildtype mice were rendered septic by cecum ligation and puncture (CLP). Cardiac function was analyzed by serial echocardiography, in vivo pressure and isolated heart measurements. Cardiac output (CO) increased to 160 % of baseline at 10 h after sepsis induction followed by a decline to 63 % of baseline after 18 h in wildtype mice. CO was unaltered in septic NOS3(-/-) mice. Despite the hyperdynamic state, cardiac function and mean arterial pressure were impaired in septic wildtype as early as 6 h post CLP. At 12 h, cardiac function in septic wildtype was refractory to catecholamines in vivo and respective isolated hearts showed impaired pressure development and limited coronary flow reserve. Hemodynamics remained stable in NOS3(-/-) mice leading to significant survival benefit. Unselective NOS inhibition in septic NOS3(-/-) mice diminished this survival benefit. Plasma NO( x )- and local myocardial NO( x )- and NO levels (via NO spin trapping) demonstrated enhanced NO( x )- and bioactive NO levels in septic wildtype as compared to NOS3(-/-) mice. Significant contribution by inducible NOS (NOS2) during this early phase of sepsis was excluded. Our data suggest that NOS3 relevantly contributes to bioactive NO pool in developing sepsis resulting in impaired cardiac contractility.

Cardiac dysfunction in adipose triglyceride lipase deficiency: treatment with a PPARα agonist

BACKGROUND AND PURPOSE

Adipose triglyceride lipase (ATGL) has been identified as a rate-limiting enzyme of mammalian triglyceride catabolism. Deletion of the ATGL gene in mice results in severe lipid accumulation in a variety of tissues including the heart. In the present study we investigated cardiac function in ATGL-deficient mice and the potential therapeutic effects of the PPARα and γ agonists Wy14,643 and rosiglitazone, respectively.

EXPERIMENTAL APPROACH

Hearts isolated from wild-type (WT) mice and ATGL(-/-) mice treated with Wy14,643 (PPARα agonist), rosiglitazone (PPARγ agonist) or vehicle were perfused at a constant flow using the Langendorff technique. Left ventricular (LV) pressure–volume relationships were established, and the response to adrenergic stimulation was determined with noradrenaline (NA).

KEY RESULTS

Hearts from ATGL(-/-) mice generated higher LV end-diastolic pressure and lower LV developed pressure as a function of intracardiac balloon volume compared to those from WT mice. Likewise, passive wall stress was increased and active wall stress decreased in ATGL(-/-) hearts. Contractile and microvascular responses to NA were substantially reduced in ATGL(-/-) hearts. Cardiac contractility was improved by treating ATGL(-/-) mice with the PPARα agonist Wy14,643 but not with the PPARγ agonist rosiglitazone.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that lipid accumulation in mouse hearts caused by ATGL gene deletion severely affects systolic and diastolic function, as well as the response to adrenergic stimulation. The beneficial effects of Wy14,643 suggest that the cardiac phenotype of these mice is partially due to impaired PPARα signalling.

Sub-cellular targeting of constitutive NOS in health and disease

Constitutive nitric oxide synthases (NOSs) are ubiquitous enzymes that play a pivotal role in the regulation of myocardial function in health and disease. The discovery of both a neuronal NOS (nNOS) and an endothelial NOS (eNOS) isoform in the myocardium and the availability of genetically modified mice with selective eNOS or nNOS gene deletion have been of crucial importance for understanding the role of constitutive nitric oxide (NO) production in the myocardium. eNOS and nNOS are homologous in structure and utilize the same co-factors and substrates; however, they differ in their subcellular localization, regulation, and downstream signaling, all of which may account for their distinct effects on excitation-contraction coupling. In particular, eNOS-derived NO has been reported to increase left ventricular (LV) compliance, attenuate beta-adrenergic inotropy and enhance parasympathetic/muscarinic responses, and mediate the negative inotropic response to β3 adrenoreceptor stimulation via cGMP-dependent signaling. Conversely, nNOS-derived NO regulates basal myocardial inotropy and relaxation by inhibiting the sarcolemmal Ca(2+) current (I(Ca)) and promoting protein kinase A-dependent phospholamban (PLN) phosphorylation, independent of cGMP. By inhibiting the activity of myocardial oxidase systems, nNOS regulates the redox state of the myocardium and contributes to maintain eNOS "coupled" activity. After myocardial infarction, up-regulation of myocardial nNOS attenuates adverse remodeling and prevents arrhythmias whereas uncoupled eNOS activity in murine models of left ventricular pressure overload accelerates the progress towards heart failure. Here we review the evidence in support of the idea that NOS subcellular localization, mode of activation, and downstream signaling account for the diverse and highly specialized actions of NO in the heart. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

[Influence of metabolism modifiers of cyclic nucleotides on contractility of right ventricle of rat heart with intact and removed endocardial endothelium]

INTRODUCTION

Endocardial endothelium, a natural biological barrier between circulating blood in heart ventricle and cells, creates a complex yet finely tuned balance of interactions with the immediate environment.

OBJECTIVE

We investigated the roles of theophylline, nonspecific phosphodiesterase inhibitor, and imidazole, an activator of phosphodiesterase on contractility of the right ventricle of rat heart, with intact and removed endocardial endothelium.

METHODS

Adult rats, of both sexes, type Wistar albino, were used in this experiment. All experiments were conducted on the preparations of the right ventricle using two experimental models. In the first experimental model, an endocardial endothelium (EE) was preserved, and in the second model, an endocardial endothelium (-EE) was removed using 1% solution Triton X-100.

RESULTS

Theophylline (1 x 10(-2) mol/l) expressed the positive inotropic effect on the heart, regardless of the presence of the endocardial endothelium. Inotropic response as multiple process can be induced by inhibition of phosphodiesterase, accumulation of cyclic nucleotides and activation of Ca2+ channels. Imidazole (2 x 10(-3) mol/l) increased the contractility of the right ventricle of the heart with EE. The modulator effect of endocardial endothelium on contractility of imidazole proved to be significant. As imidazole influenced the contractility of the right ventricle only in the presence of the endocardial endothelium, it is assumed that its effect is mediated via deliverance of endothelial mediators with positive inotropic effect.

CONCLUSION

An intact endocardial endothelium is necessary for completion of contractile performance of the heart.

PKC-δ signalling pathway is involved in H9c2 cells differentiation

H9c2 are rat heart embryonic myoblasts, with skeletal muscle properties, which terminally differentiate by fusing and forming multinucleated myotubes. Here we investigated the possible involvement of Protein Kinases C (PKCs) in H9c2 cell differentiation and explored the interplay of these enzymes both with reactive oxygen species (ROS), upstream physiological mediators of cell differentiation, and with nitric oxide (NO), downstream target of PKC activation, known for being involved in apoptosis induction in differentiated myoblasts. Cells were induced to differentiate (6 days) under low serum culture conditions and assayed for the expression of cell cycle (cyclin A) and differentiation markers (morphology and myogenin). Both ROS and in vivo production of NO were found increased after 6 days of differentiation, when the activation of PKC-δ isoform was 14-fold increased compared with the undifferentiated control cells. The parallel analysis of apoptotic features demonstrated a small increase in Annexin-V+ cells and a concomitant increase in PARP cleavage and Bax expression. Interestingly, a reduced percentage of differentiated cells was obtained both in the presence of Rottlerin, a highly selective PKC-δ pharmacologic inhibitor, and, moreover, with the use of PKC-δ siRNA technology, further supporting the involvement of PKC-δ in switching on the events related to skeletal muscle myoblast differentiation.

Nitric oxide synthases in the pathogenesis of cardiovascular disease: lessons from genetically modified mice

Nitric oxide (NO) is produced in almost all tissues and organs, exerting a variety of biological actions under both physiological and pathological conditions. NO is synthesized by three distinct NO synthase (NOS) isoforms (neuronal, inducible, and endothelial NOS), all of which are expressed in the human cardiovascular system. Although the regulatory roles of NOSs in cardiovascular diseases have been described in pharmacological studies with selective and non-selective NOS inhibitors, the specificity of the NOS inhibitors continues to be an issue of debate. To overcome this issue, genetically engineered animals have been used. All types of NOS gene-deficient animals, including singly, doubly, and triply NOS-deficient mice, and various types of NOS gene-transgenic (TG) animals, including conditional and non-conditional TG mice bearing endothelium-specific or cardiomyocyte-specific overexpression of each NOS gene, have thus been developed. The roles of individual NOS isoforms as well as the entire NOS system in the cardiovascular system have been extensively investigated in those mice, providing pivotal insights into an understanding of the pathophysiology of NOSs in human cardiovascular diseases. Based on studies with the murine NOS genetic models, this review briefly summarizes the latest knowledge of NOSs and cardiovascular diseases.

Ablation of iNOS delays cardiac contractile dysfunction in chronic hypertension

We investigated the role of inducible NOS (iNOS) on cardiac function during the development of left ventricular hypertrophy. Hypertrophy was induced by pressure-overload via short-term (2.5 months) or long-term (6.5 months) aortic banding (AoB) in wild-type (WT) and iNOS knock out (iNOSKO) mice. Cardiac function was then assessed via echocardiography, in situ hemodynamics and papillary muscle force measurements. Quantitative RT-PCR and Western blots were used to measure expression of hypertrophic gene markers and proteins respectively. Our data demonstrate that increased afterload via AoB leads to increased expression of iNOS that is associated with cardiac dysfunction. In pressure-overload induced hypertrophy, iNOSKO delays both the expression of hypertrophic markers and contractile dysfunction without causing significant changes in the level of hypertrophy. Moreover, after long-term AoB, iNOSKO animals exhibited increased basal cardiac function and an improved response to beta-adrenergic stimulation compared to long-term AoB WT animals. In conclusion, our data demonstrate that NO production via iNOS plays an important role in modulating cardiac function after moderate AoB that mimics long-term hypertension in humans.

The exercising heart at altitude

Maximal cardiac output is reduced in severe acute hypoxia but also in chronic hypoxia by mechanisms that remain poorly understood. In theory, the reduction of maximal cardiac output could result from: (1) a regulatory response from the central nervous system, (2) reduction of maximal pumping capacity of the heart due to insufficient coronary oxygen delivery prior to the achievement of the normoxic maximal cardiac output, or (3) reduced central command. In this review, we focus on the effects that acute and chronic hypoxia have on the pumping capacity of the heart, particularly on myocardial contractility and the molecular responses elicited by acute and chronic hypoxia in the cardiac myocytes. Special emphasis is put on the cardioprotective effects of chronic hypoxia.

Nitric oxide and nitric oxide synthase isoforms in the normal, hypertrophic, and failing heart

Nitric oxide (NO) produced in the heart by nitric oxide synthase (NOS) is a highly reactive signaling molecule and an important modulator of myocardial function. NOS catalyzes the conversion of L: -arginine to L: -citrulline and NO but under particular circumstances reactive oxygen species (ROS) can be formed instead of NO (uncoupling). In the heart, three NOS isoforms are present: neuronal NOS (nNOS, NOS1) and endothelial NOS (eNOS, NOS3) are constitutively present enzymes in distinct subcellular locations within cardiomyocytes, whereas inducible NOS (iNOS, NOS2) is absent in the healthy heart, but its expression is induced by pro-inflammatory mediators. In the tissue, NO has two main effects: (i) NO stimulates the activity of guanylate cyclase, leading to cGMP generation and activation of protein kinase G, and (ii) NO nitrosylates tyrosine and thiol-groups of cysteine in proteins. Upon nitrosylation, proteins may change their properties. Changes in (i) NOS expression and activity, (ii) subcellular compartmentation of NOS activity, and (iii) the occurrence of uncoupling may lead to multiple NO-induced effects, some of which being particularly evident during myocardial overload as occurs during aortic constriction and myocardial infarction. Many of these NO-induced effects are considered to be cardioprotective but particularly if NOS becomes uncoupled, formation of ROS in combination with a low NO bioavailability predisposes for cardiac damage.

Endothelial nitric oxide synthase promotes bone marrow stromal cell migration to the ischemic myocardium via upregulation of stromal cell-derived factor-1alpha

The aim of this study was to investigate the role of endothelial nitric oxide synthase (eNOS) in the host myocardium on bone marrow mesenchymal stromal cells (MSC) migration to the ischemic myocardium and whether stromal cell-derived factor-1alpha (SDF-1alpha) contributes to eNOS-mediated MSC migration. MSCs and coronary microvascular endothelial cells were isolated from adult wild-type (WT) mouse bone marrow and hearts, respectively. Cultured neonatal cardiomyocytes from WT, eNOS(-/-), and eNOS overexpressing transgenic (Tg) mice were subjected to anoxia and reoxygenation (A/R), and the conditioned medium was used as a chemoattractant for in vitro transendothelial migration assay. MSC migration was decreased in the presence of conditioned medium derived from eNOS(-/-) cardiomyocytes but increased in the presence of eNOS-Tg conditioned medium. SDF-1alpha expression was decreased in eNOS(-/-) but increased in eNOS-Tg cardiomyocytes following A/R and in the myocardium following ischemia/reperfusion (I/R). SDF-1alpha expression was cGMP-dependent as inhibition of soluble guanylyl cyclase decreased SDF-1alpha expression in WT cardiomyocytes. MSCs expressed very low levels of eNOS proteins compared with the adult myocardium. To examine MSC migration in vivo, MSCs derived from mice expressing enhanced green fluorescence protein (EGFP(+)) were intravenously administered to WT mice subjected to myocardial I/R. EGFP(+) cells in the ischemic region were decreased in eNOS(-/-) but increased in eNOS-Tg compared with WT hearts. MSC treatment improved cardiac function following I/R in WT but not in eNOS(-/-) mice. In conclusion, eNOS in the host myocardium promotes MSC migration to the ischemic myocardium and improves cardiac function through cGMP-dependent increases in SDF-1alpha expression.

Cyclic GMP signaling in cardiovascular pathophysiology and therapeutics

Cyclic guanosine 3',5'-monophosphate (cGMP) mediates a wide spectrum of physiologic processes in multiple cell types within the cardiovascular system. Dysfunctional signaling at any step of the cascade - cGMP synthesis, effector activation, or catabolism - have been implicated in numerous cardiovascular diseases, ranging from hypertension to atherosclerosis to cardiac hypertrophy and heart failure. In this review, we outline each step of the cGMP signaling cascade and discuss its regulation and physiologic effects within the cardiovascular system. In addition, we illustrate how cGMP signaling becomes dysregulated in specific cardiovascular disease states. The ubiquitous role cGMP plays in cardiac physiology and pathophysiology presents great opportunities for pharmacologic modulation of the cGMP signal in the treatment of cardiovascular diseases. We detail the various therapeutic interventional strategies that have been developed or are in development, summarizing relevant preclinical and clinical studies.

Nitric oxide synthases and cardiovascular diseases: insights from genetically modified mice

Nitric oxide (NO) is produced in almost all tissues and organs, exerting a variety of biological actions under both physiological and pathological conditions. NO is synthesized by 3 distinct NO synthase (NOS) isoforms (neuronal, inducible, and endothelial NOS), all of which are expressed in the human cardiovascular system. The regulatory roles of NOSs in cardiovascular diseases have been described in pharmacological studies with selective and non-selective NOS inhibitors. However, the specificity of the NOS inhibitors continues to be an issue of debate. To overcome this issue, genetically engineered animals have been used. All types of NOS gene-deficient (knockout: KO) animals, including singly, doubly, and triply NOS-KO mice, and various types of NOS gene-transgenic (TG) animals, including conditional and non-conditional TG mice bearing endothelium-specific or cardiomyocyte-specific overexpression of each NOS gene, have thus far been developed. The roles of individual NOS isoforms, as well as the entire NOS system, in the cardiovascular system have been extensively investigated in those mice, and the results provide pivotal insights into the pathophysiology of NOSs in human cardiovascular diseases. Based on studies with murine NOS genetic models, this review summarizes the latest knowledge of NOSs and cardiovascular diseases.

Isoproterenol-induced heart failure in the rat is associated with nitric oxide-dependent functional alterations of cardiac function

AIMS

The role of nitric oxide (NO) in heart failure (HF) is complex and remains controversial. We tested the hypothesis that the role of NO in isolated atria and cardiomyocytes is altered in isoproterenol-induced HF.

METHODS AND RESULTS

Rats received isoproterenol (ISO, 5 mg/kg/day, intraperitoneally) or vehicle for 1 week. Haemodynamic parameters were obtained by left ventricular catheterization. Effects of NOS inhibition on isolated atria and on electrically paced left ventricular myocytes were determined. Additionally, expressions of nitric oxide synthases and their allosteric modulators hsp90, caveolin-1, and caveolin-3 proteins in the left ventricles were measured. ISO increased left ventricular mass by 33% and decreased indices of left ventricular systolic and diastolic function dp/dtmin and dp/dtmax (both P<0.05). Isolated atria from HF rats had a lower spontaneous beating rate (P<0.05). NOS inhibition by L-NAME increased basal frequency and attenuated the positive chronotropic effect of beta-adrenergic stimulation in the HF group (P<0.05). Ventricular myocytes from failing hearts had impaired cell shortening. L-NAME decreased contractility of control, but not failing myocytes. Left ventricular expressions of eNOS, hsp90, iNOS, but not nNOS or caveolins, were increased.

CONCLUSION

Despite the increased capacity for NO synthesis in isoproterenol-induced HF, NO does not sustain contractility of failing myocytes. NO may contribute to the decreased basal heart rate and it may accelerate beta-adrenergic stimulation of chronotropy.

Phosphodiesterase 5 restricts NOS3/Soluble guanylate cyclase signaling to L-type Ca2+ current in cardiac myocytes

Endothelial nitric oxide synthase (NOS3) regulates the functional response to beta-adrenergic (beta-AR) stimulation via modulation of the L-type Ca(2+) current (I(Ca)). However, the NOS3 signaling pathway modulating I(Ca) is unknown. This study investigated the contribution of soluble guanylate cyclase (sGC) and phosphodiesterase type 5 (PDE5), a cGMP-specific PDE, in the NOS3-mediated regulation of I(Ca). Myocytes were isolated from NOS3 knockout (NOS3(-/-)) and wildtype (WT) mice. We measured I(Ca) (whole-cell voltage-clamp), and simultaneously measured Ca(2+) transients (Fluo-4 AM) and cell shortening (edge detection). Zaprinast (selective inhibitor of PDE5), decreased beta-AR stimulated (isoproterenol, ISO)-I(Ca), and Ca(2+) transient and cell shortening amplitudes in WT myocytes. However, YC-1 (NO-independent activator of sGC) only reduced ISO-stimulated I(Ca), but not cardiac contraction. We further investigated the NOS3/sGC/PDE5 pathway in NOS3(-/-) myocytes. PDE5 is mislocalized in these myocytes and we observed dissimilar effects of PDE5 inhibition and sGC activation compared to WT. That is, zaprinast had no effect on ISO-stimulated I(Ca), or Ca(2+) transient and cell shortening amplitudes. Conversely, YC-1 significantly decreased both ISO-stimulated I(Ca), and cardiac contraction. Further confirming that PDE5 localizes NOS3/cGMP signaling to I(Ca); YC-1, in the presence of zaprinast, now significantly decreased ISO-stimulated Ca(2+) transient and cell shortening amplitudes in WT myocytes. The effects of YC-1 on I(Ca) and cardiac contraction were blocked by KT5823 (a selective inhibitor of the cGMP-dependent protein kinase, PKG). Our data suggests a novel physiological role for PDE5 in restricting the effects of NOS3/sGC/PKG signaling pathway to modulating beta-AR stimulated I(Ca), while limiting effects on cardiac contraction.

Differential roles of nitric oxide synthase isozymes in cardiotoxicity and mortality following chronic doxorubicin treatment in mice

The roles of individual nitric oxide synthases (NOS) in anthracycline-related cardiotoxicity are not completely understood. We investigated the effects of a chronic treatment with doxorubicin (DOX) on knockouts of the individual NOS isozymes and on transgenic mice with myocardial overexpression of eNOS. Fractional shortening (FS) was reduced in untreated homozygous nNOS and iNOS knockouts as well as in eNOS transgenics. DOX-induced FS decrease in wild-type mice was attenuated only in eNOS knockouts, which were found to overexpress nNOS. No worsening of contractility was observed in DOX-treated eNOS transgenics and iNOS knockouts. Although the surviving DOX-treated nNOS knockouts exhibited no further impairment in contractility, most (70%) animals died within 7 weeks after treatment onset. In comparison to untreated wild-type hearts, the nitric oxide (NO) level was lower in hearts from DOX-treated wild-type mice and in all three untreated knockouts. DOX treatment had no effect on NO in the knockouts. These data indicate differential roles of the individual NOS in DOX-induced cardiotoxicity. Protection against DOX effects conferred by eNOS deletion may be mediated by a compensatory overexpression of nNOS. NOS inhibition-based prevention of anthracycline-induced cardiotoxicity should be eNOS-selective, simultaneously avoiding inhibiting nNOS.

Designing heart performance by gene transfer

The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.

Nitric oxide signaling and the regulation of myocardial function

Nitric oxide, which is produced endogenously within cardiac myocytes by three distinct isoforms of nitric oxide synthase, is a key regulator of myocardial function. This review will focus on the regulation of myocardial function by each nitric oxide synthase isoform during health and disease, with a specific emphasis on the proposed end-targets and signaling pathways.

Constitutive nitric oxide synthases in the heart from hypertrophy to failure

1. Endogenous myocardial nitric oxide (NO) may modulate the transition from adaptive to maladaptive hypertrophy leading to heart failure. This review summarizes the information on the interrelations between the precise localization of NO synthases (NOS) and their regulatory functions within different compartments of the heart. 2. In rodent models of pressure overload or myocardial infarction, the three NOS isoforms (NOS1, NOS2, NOS3) were shown to play a neutral, protective, or even adverse role in myocardial remodelling, depending on the NOS activity, the location of each NOS and their regulators. 3. The analysis of conditions that modulate the expression of NOS1 and NOS3 in the heart according to physiopathological situations, indicated that, beside the level of total NOS activity, unique changes in NO compartmentation secondary to NOS1 or NOS3 subcellular location might be involved in the development of cardiac hypertrophy and failure. 4. Thus, different circuits in NO-signalling pathways in myocardium might be activated and this principle is a key to understand contradictions existing in NO biology in the heart. Unravelling the mechanisms behind the NO, NOS and cardiac function is still an ongoing challenge.

Myocardial hypertrophy in the absence of external stimuli is induced by angiogenesis in mice

Although studies have suggested a role for angiogenesis in determining heart size during conditions demanding enhanced cardiac performance, the role of EC mass in determining the normal organ size is poorly understood. To explore the relationship between cardiac vasculature and normal heart size, we generated a transgenic mouse with a regulatable expression of the secreted angiogenic growth factor PR39 in cardiomyocytes. A significant change in adult mouse EC mass was apparent by 3 weeks following PR39 induction. Heart weight; cardiomyocyte size; vascular density normalization; upregulation of hypertrophy markers including atrial natriuretic factor, beta-MHC, and GATA4; and activation of the Akt and MAP kinase pathways were observed at 6 weeks post-induction. Treatment of PR39-induced mice with the eNOS inhibitor L-NAME in the last 3 weeks of a 6-week stimulation period resulted in a significant suppression of heart growth and a reduction in hypertrophic marker expression. Injection of PR39 or another angiogenic growth factor, VEGF-B, into murine hearts during myocardial infarction led to induction of myocardial hypertrophy and restoration of myocardial function. Thus stimulation of vascular growth in normal adult mouse hearts leads to an increase in cardiac mass.

Boveris A, T. Arranz C, Balaszczuk AM. Cardiac mitochondrial nitric oxide: a regulator of heart rate?

Alterations in autonomic control and myocardial nitric-oxide (NO) production are likely linked to the development and progression of heart dysfunction. By focusing on heart rate, the complexity of the actions of NO at distinct levels throughout the autonomic nervous system and its relationship with other regulators can be demonstrated. Given the multiple and opposing actions of NO on cardiac control, it is difficult to interpret a response after a global intervention in the NO system. The diversity of intracellular pathways activated by NO, and their differing sensitivities to different levels of NO, might account for some aspects of reported specific but opposite effects. We discuss factors that might contribute to this diversity of actions. A proper elucidation of the effects of NO on metabolic pathways and on energy generation could lead to novel therapeutic strategies aimed at the early treatment of heart dysfunction.

Cardiac Oxidative Stress Is Elevated at the Onset of Dilated Cardiomyopathy in Streptozotocin-Diabetic Rats

The association between nitric oxide synthase (eNOS and iNOS) status, oxidative stress, and cardiac function was evaluated in streptozotocin (STZ)-diabetic rats to understand the etiology of diabetic cardiomyopathy. Cardiac function was determined by echocardiography. eNOS and iNOS status and superoxide production were assessed by immunohistochemistry and chemiluminescence, respectively. In STZ-diabetic rats, stroke volume, cardiac output, and left ventricular ejection fraction were significantly lower than in controls (CT, P < .05), whereas left ventricular end-systolic volume was higher. Cardiac NOS activity increased from 161 ± 18 cpm/mg tissue in CT rats to 286 ± 20 cpm/mg tissue ( P < .001) in STZ-diabetic rats. Furthermore, superoxide production and cardiac eNOS and iNOS levels were higher in STZ-diabetic rats than in CT rats ( P < .05). An increased activation of cardiac eNOS and iNOS is observed concomitantly with decreased cardiac function. Thus, increased oxidative stress in the heart may be implicated in the development of dilated cardiomyopathy in STZ-diabetic rats.

Endothelial nitric oxide synthase decreases beta-adrenergic responsiveness via inhibition of the L-type Ca2+ current

Signaling via endothelial nitric oxide synthase (NOS3) limits the heart's response to beta-adrenergic (beta-AR) stimulation, which may be protective against arrhythmias. However, mechanistic data are limited. Therefore, we performed simultaneous measurements of action potential (AP, using patch clamp), Ca2+ transients (fluo 4), and myocyte shortening (edge detection). L-type Ca2+ current (ICa) was directly measured by the whole cell ruptured patch-clamp technique. Myocytes were isolated from wild-type (WT) and NOS3 knockout (NOS3-/-) mice. NOS3-/- myocytes exhibited a larger incidence of beta-AR (isoproterenol, 1 microM)-induced early afterdepolarizations (EADs) and spontaneous activity (defined as aftercontractions). We also examined ICa, a major trigger for EADs. NOS3-/- myocytes had a significantly larger beta-AR-stimulated increase in ICa compared with WT myocytes. In addition, NOS3-/- myocytes had a larger response to beta-AR stimulation compared with WT myocytes in Ca2+ transient amplitude, shortening amplitude, and AP duration (APD). We observed similar effects with specific NOS3 inhibition [L-N5-(1-iminoethyl)-ornithine (l-NIO), 10 microM] in WT myocytes as with NOS3 knockout. Specifically, l-NIO further increased isoproterenol-stimulated EADs and aftercontractions. l-NIO also further increased the isoproterenol-stimulated ICa, Ca2+ transient amplitude, shortening amplitude, and APD (all P < 0.05 vs isoproterenol alone). l-NIO had no effect in NOS3-/- myocytes. These results indicate that NOS3 signaling inhibits the beta-AR response by reducing ICa and protects against arrhythmias. This mechanism may play an important role in heart failure, where arrhythmias are increased and NOS3 expression is decreased.

Sympathetic control of heart rate in nNOS knockout mice

Inhibition of neuronal nitric oxide synthase (nNOS) in cardiac postganglionic sympathetic neurons leads to enhanced cardiac sympathetic responsiveness in normal animals, as well as in animal models of cardiovascular diseases. We used isolated atria from mice with selective genetic disruption of nNOS (nNOS(-/-)) and their wild-type littermates (WT) to investigate whether sympathetic heart rate (HR) responses were dependent on nNOS. Immunohistochemistry was initially used to determine the presence of nNOS in sympathetic [tyrosine hydroxylase (TH) immunoreactive] nerve terminals in the mouse sinoatrial node (SAN). After this, the effects of postganglionic sympathetic nerve stimulation (1-10 Hz) and bath-applied norepinephrine (NE; 10(-8)-10(-4) mol/l) on HR were examined in atria from nNOS(-/-) and WT mice. In the SAN region of WT mice, TH and nNOS immunoreactivity was virtually never colocalized in nerve fibers. nNOS(-/-) atria showed significantly reduced HR responses to sympathetic nerve activation and NE (P < 0.05). Similarly, the positive chronotropic response to the adenylate cyclase activator forskolin (10(-7)-10(-5) mol/l) was attenuated in nNOS(-/-) atria (P < 0.05). Constitutive NOS inhibition with L-nitroarginine (0.1 mmol/l) did not affect the sympathetic HR responses in nNOS(-/-) and WT atria. The paucity of nNOS in the sympathetic innervation of the mouse SAN, in addition to the attenuated HR responses to neuronal and applied NE, indicates that presynaptic sympathetic neuronal NO does not modulate neuronal NE release and SAN pacemaking in this species. It appears that genetic deletion of nNOS results in the inhibition of adrenergic-adenylate cyclase signaling within SAN myocytes.

Characterization of myocardial hypertrophy in prehypertensive spontaneously hypertensive rats: interaction between adrenergic and nitrosative pathways

OBJECTIVE AND METHODS

Left ventricular hypertrophy in human and experimental hypertension is not always associated with pressure overload but seems to precede an increase in blood pressure. In this study, performed in male 5-week-old prehypertensive spontaneously hypertensive rats (SHR; n = 65) and age-matched Wistar-Kyoto rats (n = 56), the relationship between myocardial structure and activation of the adrenergic and nitric oxide systems was evaluated.

RESULTS

Body weight, blood pressure and heart rate were similar in both groups. A higher left ventricle/body weight ratio was found in SHR, as a result of greater mononuclear (+47%) and binuclear (+43%) myocyte volumes, without changes in interstitial collagen. Both adrenergic and nitric oxide pathways were activated in SHR, as expressed by higher myocardial norepinephrine content, tyrosine hydroxylase activity, myocardial nitric oxide synthase 3 expression and protein nitration, indicating greater peroxynitrite (ONOO) generation from nitric oxide and superoxide. No difference was measured in nitric oxide synthase 1 expression, whereas nitric oxide synthase 2 was undetectable. A positive correlation between myocardial tyrosine hydroxylase activity and protein nitration was observed in SHR (r = 0.328; P < 0.01). Early treatment with a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl, from the third to the fifth week of age, reduced ONOO generation, protein nitration and sympathetic activation in SHR without changes in myocardial structure.

CONCLUSION

In prehypertensive SHR, left ventricular hypertrophy is associated with adrenergic and nitrosative imbalance. Early superoxide dismutase mimetic treatment in SHR effectively reduces higher myocardial ONOO generation, sympathetic activation, and heart rate without affecting the development of myocardial hypertrophy.

Nitric oxide in the pathogenesis of cardiac disease

Endothelial dysfunction is characterized by a vasoconstrictive and prothrombotic state in the vasculature; it plays a role in all stages of cardiac disease and is a significant independent predictor of cardiovascular outcomes. Nitric oxide (NO) performs multiple biologic activities in the endothelium, including vasodilation and antithrombotic actions. Reduced NO bioactivity is a major component of endothelial dysfunction. Impaired NO bioactivity is an important factor in the pathogenesis of atherosclerosis and in the metabolic syndrome. The functions of NO bioactivity in the heart go well beyond those in the endothelium, as all 3 NO synthase (NOS) isoforms-endothelial NOS, neuronal NOS, and inducible NOS-are expressed in cardiac myocytes and mediate systolic, diastolic, and chronotropic cardiac functions. Impairment of NO bioactivity is a pathogenic factor in various forms of cardiac disease. Although these findings support the potential use of NO-targeted therapies for treatment of cardiac disease, the complexities of the biologic actions of NO in the vasculature and heart are such that development of therapies is still largely in the preliminary stages.

Nitroxyl increases force development in rat cardiac muscle

Donors of nitroxyl (HNO), the reduced congener of nitric oxide (NO), exert positive cardiac inotropy/lusitropy in vivo and in vitro, due in part to their enhancement of Ca(2+) cycling into and out of the sarcoplasmic reticulum. Here we tested whether the cardiac action of HNO further involves changes in myofilament-calcium interaction. Intact rat trabeculae from the right ventricle were mounted between a force transducer and a motor arm, superfused with Krebs-Henseleit (K-H) solution (pH 7.4, room temperature) and loaded iontophoretically with fura-2 to determine [Ca(2+)](i). Sarcomere length was set at 2.2-2.3 microm. HNO donated by Angeli's salt (AS; Na(2)N(2)O(3)) dose-dependently increased both twitch force and [Ca(2+)](i) transients (from 50 to 1000 microm). Force increased more than [Ca(2+)](i) transients, especially at higher doses (332 +/- 33% versus 221 +/- 27%, P < 0.01 at 1000 microm). AS/HNO (250 microm) increased developed force without changing Ca(2+) transients at any given [Ca(2+)](o) (0.5-2.0 mm). During steady-state activation, AS/HNO (250 microm) increased maximal Ca(2+)-activated force (F(max), 106.8 +/- 4.3 versus 86.7 +/- 4.2 mN mm(-2), n = 7-8, P < 0.01) without affecting Ca(2+) required for 50% activation (Ca(50), 0.44 +/- 0.04 versus 0.52 +/- 0.04 microm, not significant) or the Hill coefficient (4.75 +/- 0.67 versus 5.02 +/- 1.1, not significant). AS/HNO did not alter myofibrillar Mg-ATPase activity, supporting an effect on the myofilaments themselves. The thiol reducing agent dithiothreitol (DTT, 5.0 mm) both prevented and reversed HNO action, confirming AS/HNO redox sensitivity. Lastly, NO (from DEA/NO) did not mimic AS/HNO cardiac effects. Thus, in addition to reported changes in Ca(2+) cycling, HNO also acts as a cardiac Ca(2+) sensitizer, augmenting maximal force without altering actomyosin ATPase activity. This is likely to be due to modulation of myofilament proteins that harbour reactive thiolate groups that are targets of HNO.

Role of myocardial nitric oxide in diabetic ischemia-reperfusion dysfunction: studies in mice with myocyte-specific overexpression of endothelial nitric-oxide synthase

We investigated the role of nitric oxide (NO) in myocardial ischemia-reperfusion injury of diabetic mice with myocyte-specific overexpression of endothelial NO synthase (NOS). Four weeks after diabetes induction with streptozotocin (blood glucose approximately 29 mM), isolated isovolumic heart function and cellular NO metabolites in response to brief normothermic ischemia-reperfusion were determined. Under normoxic conditions transgenic (TG) hearts from nondiabetic and diabetic animals generated less left-ventricular developed pressure compared with wild-type (WT) control hearts, and this abnormality was unaffected by NOS inhibition. During ischemia, the rise in end-diastolic pressure was less in the TG than WT group of nondiabetic hearts, whereas the transgene had no effect in the diabetic group. Similarly, the transgene also improved reperfusion systolic and diastolic function in nondiabetic but not in diabetic hearts. NOS inhibition worsened reperfusion function in diabetic hearts. Postischemic nitrite and cGMP formation were higher in nondiabetic TG than WT hearts, but in diabetic hearts cGMP was no longer elevated. The formation of reactive oxygen species (superoxide and peroxynitrite) during early reperfusion, measured by electron spin resonance spectroscopy, was similar in nondiabetic WT and TG hearts, but it was significantly higher in diabetic TG hearts. Stimulating endogenous NO production with 10 microM bradykinin more strongly reduced myocardial O(2) consumption in diabetic TG than diabetic WT hearts perfused in normoxia, whereas there was no difference after ischemia-reperfusion. Thus, providing additional endogenous NO is sufficient to protect nondiabetic hearts against ischemia-induced injury, but for a similar protection in diabetic hearts, effective scavenging of reactive oxygen species is also important.

Cardioprotective effects of atrasentan, an endothelin-A receptor antagonist, but not of nitric oxide in diabetic mice with myocyte-specific overexpression of endothelial nitric oxide synthase

1. We investigated the roles of nitric oxide (NO) and endothelin-1 (ET-1) in organ dysfunction in diabetic mice with normal genotype (wild-type, WT) or myocyte-specific overexpression of endothelial NO synthase (eNOS) (transgenic, TG) after chronic oral treatment with the endothelin-A (ETA) receptor antagonist atrasentan. 2. Mice were rendered diabetic by injection of 200 mg kg-1 streptozotocin (STZ). Experimental groups were: untreated WT diabetic (n=9), untreated TG diabetic (n=9), atrasentan-treated WT diabetic (n=9), atrasentan-treated TG diabetic (n=8) and the four corresponding nondiabetic groups (n=5). Atrasentan was administered orally via drinking water at 3 mg kg-1 per day over 28 days. All diabetic mice developed similar hyperglycaemia (27-30 mmol l-1). 3. Atrasentan treatment significantly improved left ventricular systolic and diastolic function in response to exogenous norepinephrine, but there were no differences between genotypes. 4. Atrasentan antagonized the diabetic impairments in endothelium-dependent coronary relaxation and thromboxane-receptor mediated aortic constriction. Further, it improved cardiac and renal oxidant status as evident from reduced tissue malondialdehyde levels. 5. Atrasentan reduced diabetic urine flow, proteinuria and plasma creatinine levels, but creatinine clearance was not significantly altered. 6. These results suggest that in experimental type 1 diabetes, blocking ETA receptors ameliorates myocardial, coronary and renal function and improves tissue oxidant status, whereas raising myocardial NO levels has neither beneficial nor deleterious effects on diabetic cardiomyopathy in this transgenic model.