Characterization of Glutathione Dithiophosphates as Long-Acting H2S Donors.

Considering the important cytoprotective and signaling roles but relatively narrow therapeutic index of hydrogen sulfide (H2S), advanced H2S donors are required to achieve a therapeutic effect. In this study, we proposed glutathione dithiophosphates as new combination donors of H2S and glutathione. The kinetics of H2S formation in dithiophosphate solutions suggested a continuous H2S release by the donors, which was higher for the dithiophosphate of reduced glutathione than oxidized glutathione. The compounds, unlike NaHS, inhibited the proliferation of C2C12 myoblasts at submillimolar concentrations due to an efficient increase in intracellular H2S. The H2S donors more profoundly affected reactive oxygen species and reduced glutathione levels in C2C12 myocytes, in which these parameters were elevated compared to myoblasts. Oxidized glutathione dithiophosphate as well as control donors exerted antioxidant action toward myocytes, whereas the effect of reduced glutathione dithiophosphate at (sub-)micromolar concentrations was rather modulating. This dithiophosphate showed an enhanced negative inotropic effect mediated by H2S upon contraction of the atrial myocardium, furthermore, its activity was prolonged and reluctant for washing. These findings identify glutathione dithiophosphates as redox-modulating H2S donors with long-acting profile, which are of interest for further pharmacological investigation.

Contractile Behavior of Right Atrial Myocardium of Healthy Rats and Rats with the Experimental Model of Pulmonary Hypertension.

There is a lack of data about the contractile behavior of the right atrial myocardium in chronic pulmonary heart disease. We thoroughly characterized the contractility and Ca transient of isolated right atrial strips of healthy rats (CONT) and rats with the experimental model of monocrotaline-induced pulmonary hypertension (MCT) in steady state at different preloads (isometric force-length), during slow force response to stretch (SFR), and during post-rest potentiation after a period of absence of electrical stimulation (PRP). The preload-dependent changes in the isometric twitch and Ca transient did not differ between CONT and MCT rats while the kinetics of the twitch and Ca transient were noticeably slowed down in the MCT rats. The magnitude of SFR was significantly elevated in the MCT right atrial strips and this was accompanied by the significantly higher elevation of the Ca transient relative amplitude at the end of SFR. The slow changes in the contractility and Ca transient in the PRP protocol did not differ between CONT and MCT. In conclusion, the alterations in the contractility and Ca transient of the right atrial myocardium of monocrotaline-treated rats with pulmonary hypertension mostly concern the elevation in SFR. We hypothesize that this positive inotropic effect in the atrial myocardium may (partly) compensate the systolic deficiency of the right ventricular failing myocardium.

The behavior of three types of large sinus node arteries with regard to the blood supply of the atrial myocardium.

PURPOSE: We describe angiographic findings of sinus node arteries (SNAs), focusing in the large sinus node artery (LSNA) variants, regarding the blood supply of the SN and atrial myocardium. METHODS: We examined the SN arteries via postmortem angiographic visualization in six hundred hearts derived from victims of various accidents. RESULTS: The main stem or a branch of the SNA supplied the right atrium (RA) and part of the interatrial septum (IS) in 32% of cases (Group A), one atrium, the IS and a small part of the other atrium (Group B) in 39% and the entire atrial myocardium (LSNAs) (Group C) in 29%. Forty-two percent (42%) of LSNAs were arising from the anterior part of the right coronary artery (RCA) (type 1), 9% from its intermediate part (type 2) and 49% from the posterolateral portion of the left circumflex artery (LCx) (type 3). Type 2 can be injured by surgical procedures, type 3 by interventional ones, while type 1 is not affected by any. The SN area was supplied in Groups A and B by the main stem of SN arteries in 370 cases (62%) and by branches (Br) in 55 (9%). The 175 cases of group C (29%) were supplied only by branches. The clockwise (40% of cases) and counterclockwise rotations (60%) of the SNA around the superior vena cava, concern surgical procedures. CONCLUSION: The above findings are essential for every day surgical and interventional procedures.

Reduced nNOS activity is responsible for impaired fatty acid-dependent mitochondrial oxygen consumption in atrial myocardium from hypertensive rat.

Fatty acid (FA)-dependent mitochondrial activities of atrial myocardium in hypertension (HTN) and its regulation by nitric oxide (NO) remain unidentified. Here, we have studied palmitic acid (PA) regulation of cardiac mitochondrial oxygen consumption rate (OCR) in left atrial (LA) myocardium of sham and angiotensin II-induced HTN rats and their regulations by endothelial NO synthase (eNOS) and neuronal NO synthase (nNOS). The effects were compared with those of left ventricular (LV) myocytes. Our results showed that OCR was greater in HTN-LA compared with that in sham-LA. PA increased OCR in sham-LA, sham-LV, and HTN-LV but reduced it in HTN-LA. Inhibition of nNOS (S-methyl-L-thiocitrulline, SMTC) or eNOS/nNOS (Nω-nitro-L-arginine methyl ester hydrochloride, L-NAME) reduced PA increment of OCR in sham-LA but exerted no effect on OCR in HTN-LA. SMTC reduced OCR in HTN-LV and L-NAME reduced OCR in sham-LV. nNOS was the predominant source of NO in LA and LV. nNOS-derived NO was increased in HTN-LA and HTN-LV. PA reduced eNOSSer1177, nNOSSer1417, and NO level in HTN-LA but exerted no effect in sham-LA. In contrast, PA increased NO in HTN-LV and enhanced nNOSSer1417 but reduced NO level in sham-LV without affecting eNOSSer1177, eNOSThr495, or nNOSSer1417. 2-Bromopalmitate (2BP), which blocks the S-palmitoylation of target proteins, prevented PA-dependent decrease of nNOSSer1417 and OCR in HTN-LA. In HTN-LV, 2BP prevented PA-induced OCR without affecting nNOSSer1417. Our results reveal that FA-induced mitochondrial activity in atrial myocardium is impaired in HTN which is mediated by reduced nNOS activity and NO bioavailability. Metabolic dysregulation may underlie diastolic dysfunction of atrial myocardium in HTN.

Acute interaction between human epicardial adipose tissue and human atrial myocardium induces arrhythmic susceptibility.

Epicardial adipose tissue (EAT) deposition has a strong clinical association with atrial arrhythmias; however, whether a direct functional interaction exists between EAT and the myocardium to induce atrial arrhythmias is unknown. Therefore, we aimed to determine whether human EAT can be an acute trigger for arrhythmias in human atrial myocardium. Human trabeculae were obtained from right atrial appendages of patients who have had cardiac surgery (n = 89). The propensity of spontaneous contractions (SCs) in the trabeculae (proxy for arrhythmias) was determined under physiological conditions and during known triggers of SCs (high Ca2+, ß-adrenergic stimulation). To determine whether EAT could trigger SCs, trabeculae were exposed to superfusate of fresh human EAT, and medium of 24 h-cultured human EAT treated with ß1/2 (isoproterenol) or ß3 (BRL37344) adrenergic agonists. Without exposure to EAT, high Ca2+ and ß1/2-adrenergic stimulation acutely triggered SCs in, respectively, 47% and 55% of the trabeculae that previously were not spontaneously active. Acute ß3-adrenergic stimulation did not trigger SCs. Exposure of trabeculae to either superfusate of fresh human EAT or untreated medium of 24 h-cultured human EAT did not induce SCs; however, specific ß3-adrenergic stimulation of EAT did trigger SCs in the trabeculae, either when applied to fresh (31%) or cultured (50%) EAT. Additionally, fresh EAT increased trabecular contraction and relaxation, whereas media of cultured EAT only increased function when treated with the ß3-adrenergic agonist. An acute functional interaction between human EAT and human atrial myocardium exists that increases the propensity for atrial arrhythmias, which depends on ß3-adrenergic rather than ß1/2-adrenergic stimulation of EAT.

Transcriptome analysis defines myocardium gene signatures in children with ToF and ASD and reveals disease-specific molecular reprogramming in response to surgery with cardiopulmonary bypass.

BACKGROUND: Tetralogy of Fallot (ToF) and Atrial Septal Defects (ASD) are the most common types of congenital heart diseases and a major cause of childhood morbidity and mortality. Cardiopulmonary bypass (CPB) is used during corrective cardiac surgery to support circulation and heart stabilization. However, this procedure triggers systemic inflammatory and stress response and consequent increased risk of postoperative complications. The aim of this study was to define the molecular bases of ToF and ASD pathogenesis and response to CPB and identify new potential biomarkers. METHODS: Comparative transcriptome analysis of right atrium specimens collected from 10 ToF and 10 ASD patients was conducted before (Pre-CPB) and after (Post-CPB) corrective surgery. Total RNA isolated from each sample was individually hybridized on Affymetrix HG-U133 Plus Array Strips containing 38,500 unique human genes. Differences in the gene expression profiles and functional enrichment/network analyses were assessed using bioinformatic tools. qRT-PCR analysis was used to validate gene modulation. RESULTS: Pre-CPB samples showed significant differential expression of a total of 72 genes, 28 of which were overexpressed in ToF and 44 in ASD. According to Gene Ontology annotation, the mostly enriched biological processes were represented by matrix organization and cell adhesion in ToF and by muscle development and contractility in ASD specimens. GSEA highlighted the specific enrichment of hypoxia gene sets in ToF samples, pointing to a role for hypoxia in disease pathogenesis. The post-CPB myocardium exhibited significant alterations in the expression profile of genes related to transcription regulation, growth/apoptosis, inflammation, adhesion/matrix organization, and oxidative stress. Among them, only 70 were common to the two disease groups, whereas 110 and 24 were unique in ToF and ASD, respectively. Multiple functional interactions among differentially expressed gene products were predicted by network analysis. Interestingly, gene expression changes in ASD samples followed a consensus hypoxia profile. CONCLUSION: Our results provide a comprehensive view of gene reprogramming in right atrium tissues of ToF and ASD patients before and after CPB, defining specific molecular pathways underlying disease pathophysiology and myocardium response to CPB. These findings have potential translational value because they identify new candidate prognostic markers and targets for tailored cardioprotective post-surgical therapies.

Nr2f1a balances atrial chamber and atrioventricular canal size via BMP signaling-independent and -dependent mechanisms.

Determination of appropriate chamber size is critical for normal vertebrate heart development. Although Nr2f transcription factors promote atrial maintenance and differentiation, how they determine atrial size remains unclear. Here, we demonstrate that zebrafish Nr2f1a is expressed in differentiating atrial cardiomyocytes. Zebrafish nr2f1a mutants have smaller atria due to a specific reduction in atrial cardiomyocyte (AC) number, suggesting it has similar requirements to Nr2f2 in mammals. Furthermore, the smaller atria in nr2f1a mutants are derived from distinct mechanisms that perturb AC differentiation at the chamber poles. At the venous pole, Nr2f1a enhances the rate of AC differentiation. Nr2f1a also establishes the atrial-atrioventricular canal (AVC) border through promoting the differentiation of mature ACs. Without Nr2f1a, AVC markers are expanded into the atrium, resulting in enlarged endocardial cushions (ECs). Inhibition of Bmp signaling can restore EC development, but not AC number, suggesting that Nr2f1a concomitantly coordinates atrial and AVC size through both Bmp-dependent and independent mechanisms. These findings provide insight into conserved functions of Nr2f proteins and the etiology of atrioventricular septal defects (AVSDs) associated with NR2F2 mutations in humans.

Atrial fibrillation is associated with the fibrotic remodelling of adipose tissue in the subepicardium of human and sheep atria.

AIMS: Accumulation of atrial adipose tissue is associated with atrial fibrillation (AF). However, the underlying mechanisms remain poorly understood. We examined the relationship between the characteristics of fatty infiltrates of the atrial myocardium and the history of AF. METHODS AND RESULTS: Atrial samples, collected in 92 patients during cardiac surgery and in a sheep model of persistent AF, were subjected to a detailed histological analysis. In sections of human right atrial samples, subepicardial fatty infiltrations were commonly observed in the majority of patients. A clear difference in the appearance and fibrotic content of these fatty infiltrations was observed. Fibro-fatty infiltrates predominated in patients with permanent AF (no AF: 37 ± 24% vs. paroxysmal AF: 50 ± 21% vs. permanent AF: 64 ± 23%, P < 0.001). An inverse correlation between fibrotic remodelling and the amount of subepicardial adipose tissue suggested the progressive fibrosis of fatty infiltrates with permanent AF. This hypothesis was tested in a sheep model of AF. In AF sheep, an increased accumulation of peri-atrial fat depot was observed on cardiac magnetic resonance imaging and dense fibro-fatty infiltrations predominated in the left atria of AF sheep. Cellular inflammation, mainly consisting of functional cytotoxic T lymphocytes, was observed together with adipocyte cell death in human atria. CONCLUSION: Atrial fibrillation is associated with the fibrosis of subepicardial fatty infiltrates, a process in which cytotoxic lymphocytes might be involved. This remodelling of the atrial subepicardium could contribute to structural remodelling forming a substrate for AF.

Differential expression of microRNAs following cardiopulmonary bypass in children with congenital heart diseases.

BACKGROUND: Children with congenital heart defects (CHDs) are at high risk for myocardial failure after operative procedures with cardiopulmonary bypass (CPB). Recent studies suggest that microRNAs (miRNA) are involved in the development of CHDs and myocardial failure. Therefore, the aim of this study was to determine alterations in the miRNA profile in heart tissue after cardiac surgery using CPB. METHODS: In total, 14 tissue samples from right atrium were collected from patients before and after connection of the CPB. SurePrint™ 8 × 60K Human v21 miRNA array and quantitative reverse transcription-polymerase chain reaction (RT-qPCR) were employed to determine the miRNA expression profile from three patients before and after connection of the CPB. Enrichment analyses of altered miRNA expression were predicted using bioinformatic tools. RESULTS: According to miRNA array, a total of 90 miRNAs were significantly altered including 29 miRNAs with increased and 61 miRNAs with decreased expression after de-connection of CPB (n = 3) compared to before CPB (n = 3). Seven miRNAs had been validated using RT-qPCR in an independent cohort of 11 patients. Enrichment analyses applying the KEGG database displayed the highest correlation for signaling pathways, cellular community, cardiovascular disease and circulatory system. CONCLUSION: Our result identified the overall changes of the miRNome in right atrium tissue of patients with CHDs after CPB. The differentially altered miRNAs lay a good foundation for further understanding of the molecular function of changed miRNAs in regulating CHDs and after CPB in particular.

Cytokine Effects on Mechano-Induced Electrical Activity in Atrial Myocardium.

The role of cytokines as regulators of stretch-related mechanisms is of special importance since mechano-sensitivity plays an important role in a wide variety of biological processes. Here, we elucidate the influence of cytokine application on mechano-sensitivity and mechano-transduction. The atrial myocardial stretch induces production of interleukin (IL)-2, IL-6, IL-13, IL-17A, and IL-18 with exception of tumor necrosis factor α (TNF-α), IL-1ß, and vascular endothelial growth factor B (VEGF-B). Positive ionotropic effect was specific for VEGF-B, negative ionotropic effects were specific for TNF-α, IL-1ß, IL-2, IL-6, IL-13, IL-17A and IL-18, while IL-1α doesn't show direct ionotropic effect. The IL-2, IL-6, IL-17A, IL-18, and VEGF-B cause elongation of the APD, in comparison with the reduced APD caused by the IL-13. The TNF-α, IL-1ß, and IL-18 influences L-type Ca2+ channels, IL-2 has an inhibitory effect on the fast Na+ channels while IL-17A and VEGF-B were specific for Kir channels. With exception of the IL-1α, IL-2, and VEGF-B, all analyzed cytokines include nitric oxide dependent signaling with resultant combined effects on mechano-gated and Ca2+ channels. The relationships between these pathways and the time-dependence of their activation are of important considerations in the evaluation of cytokine-induced electrical abnormality, specific for cardiac dysfunctions. In general, the discussion presented in this review covers research devoted to counterbalance between different cytokines in the regulation of stretch-induced effects in rat atrial myocardium. ABBREVIATIONS: APs: action potentials; APD25: action potential durations to 25% of re-polarization; APD50: action potential durations to 50% of repolarization; APD90: action potential durations to 90% of repolarization; MGCs: mechanically gated channels.

Harmful Impact of Tobacco Smoking and Alcohol Consumption on the Atrial Myocardium.

Tobacco smoking and alcohol consumption are widespread exposures that are legal and socially accepted in many societies. Both have been widely recognized as important risk factors for diseases in all vital organ systems including cardiovascular diseases, and with clinical manifestations that are associated with atrial dysfunction, so-called atrial cardiomyopathy, especially atrial fibrillation and stroke. The pathogenesis of atrial cardiomyopathy, atrial fibrillation, and stroke in context with smoking and alcohol consumption is complex and multifactorial, involving pathophysiological mechanisms, environmental, and societal aspects. This narrative review summarizes the current literature regarding alterations in the atrial myocardium that is associated with smoking and alcohol.

Left Atrial Myocardium in Arterial Hypertension.

Arterial hypertension affects ≈ 1 billion people worldwide. It is associated with increased morbidity and mortality and responsible for millions of deaths each year. Hypertension mediates damage of target organs including the heart. In addition to eliciting left ventricular hypertrophy, dysfunction and heart failure, hypertension also causes left atrial remodeling that may culminate in atrial contractile dysfunction and atrial fibrillation. Here, we will summarize data on the various aspects of left atrial remodeling in (essential) hypertension gathered from studies on patients with hypertension and from spontaneously hypertensive rats, an animal model that closely mimics cardiac remodeling in human hypertension. Analyzing the timeline of remodeling processes, i.e., distinguishing between alterations occurring in prehypertension, in early hypertension and during advanced hypertensive heart disease, we will derive the potential mechanisms underlying left atrial remodeling in (essential) hypertension. Finally, we will discuss the consequences of these remodeling processes for atrial and ventricular function. The data imply that left atrial remodeling is multifactorial, starts early in hypertension and is an important contributor to the progression of hypertensive heart disease, including the development of atrial fibrillation and heart failure.

Interplay between cardiac transcription factors and non-coding RNAs in predisposing to atrial fibrillation.

There is growing evidence that putative gene regulatory networks including cardio-enriched transcription factors, such as PITX2, TBX5, ZFHX3, and SHOX2, and their effector/target genes along with downstream non-coding RNAs can play a potentially important role in the process of adaptive and maladaptive atrial rhythm remodeling. In turn, expression of atrial fibrillation-associated transcription factors is under the control of upstream regulatory non-coding RNAs. This review broadly explores gene regulatory mechanisms associated with susceptibility to atrial fibrillation-with key examples from both animal models and patients-within the context of both cardiac transcription factors and non-coding RNAs. These two systems appear to have multiple levels of cross-regulation and act coordinately to achieve effective control of atrial rhythm effector gene expression. Perturbations of a dynamic expression balance between transcription factors and corresponding non-coding RNAs can provoke the development or promote the progression of atrial fibrillation. We also outline deficiencies in current models and discuss ongoing studies to clarify remaining mechanistic questions. An understanding of the function of transcription factors and non-coding RNAs in gene regulatory networks associated with atrial fibrillation risk will enable the development of innovative therapeutic strategies.

Effect of hypothermic ischemia-reperfusion on the expression of Kir2.1 and CaMKⅡ in isolated rat atrial myocardium / 实用医学杂志

Objective To explore the molecular mechanism of prolonged atrial repolarization in rats with reperfusion atrial arrhythmia.Methods Sixteen Langendorff isolated heart perfusion models made by male SD rats were randomly divided into control group(group C,n = 8)and hypothermic ischemia-reperfusion group(group IR,n = 8).According to the occurrence of atrial arrhythmia after reperfusion,group IR was further subdivided into reperfusion non-atrial arrhythmia subgroup(group N-RAA)and reperfusion atrial arrhythmia subgroup(group R-AA).Group C was perfused with 37℃K-H solution for 120 min.In group IR,the isolated heart was perfused with 37℃K-H solution for 30 min and stopped,and the isolated heart was perfused with 4℃Thomas solution(20 mL/kg)for 60 mins.When the heart stopped for 30 mins,the isolated heart was perfused with a half dose of 4℃Thomas solution(10℃).During cardioplegia,the isolated heart was protected by low temperature Thomas solution(4℃),and then reperfused for 30 mins with 37℃K-H solution.The monophasic action potential(MAP)of the right atrium was recorded at balanced perfusion for 30 mins(T0),balanced perfusion for 105 mins in group C/reperfusion for 15 mins in group IR(T1)and balanced perfusion for 120 mins in group C/reperfusion for 30 min in group IR(T2);The duration of 50%and 90%repolarization of monophasic action potential(MAPD50 and MAPD90)was measured.After electrophysiological monitoring,the expression of Kir2.1 and CaMKⅡ in right atrium was detected by Western blot.Results Compared with T0,MAPD50 and MAPD90 at T1 and T2 were significantly prolonged in group R-AA(P<0.05),and MAPD90 at T1 and T2 in group R-NAA and group R-AA were significantly longer than those in group C(P<0.05).Compared with group R-NAA,MAPD50 and MAPD90 in group R-AA were significantly prolonged at T1 and T2(P<0.05).The results of Western blot showed that the expression of Kir2.1 in group R-NAA and group R-AA was significantly lower than that in group C(P<0.05),and that in group R-AA was significantly lower than that in group R-NAA(P<0.05).The expression of CaMKⅡ in group R-NAA and group R-AA was significantly higher than that in group C(P<0.05),and the expression of CaMKⅡ in group R-AA was significantly higher than that in group R-NAA.Conclusion The prolonged duration of atrial repolarization in rats with hypothermic ischemia-reperfusion atrial arrhythmia may be related to the down-regulation of Kir2.1 expression and the up-regulation of CaMKⅡ expression.

Septic cardiomyopathy: evidence for a reduced force-generating capacity of human atrial myocardium in acute infective endocarditis.

BACKGROUND: This study analyzes the myocardial force-generating capacity in infective endocarditis (IE) using an experimental model of isolated human atrial myocardium. In vivo, it is difficult to decide whether or not alterations in myocardial contractile behavior are due to secondary effects associated with infection such as an altered heart rate, alterations of preload and afterload resulting from valvular defects, and altered humoral processes. Our in vitro model using isolated human myocardium, in contrast, guarantees exactly defined experimental conditions with respect to preload, afterload, and contraction frequency, thus not only preventing confounding by in vivo determinants of contractility but also excluding effects of other factors associated with sepsis, hemodynamics, humoral influences, temperature, and medical treatment. METHODS: We analyzed right atrial trabeculae (diameter 0.3-0.5 mm, initial length 5 mm) from 32 patients undergoing aortic and/or mitral valve replacement for acute valve incompetence caused by IE and 65 controls receiving aortic and/or mitral valve replacement for nonendocarditic valve incompetence. Isometric force amplitudes and passive resting force values measured at optimal length in the two groups were compared using Student's t-test. RESULTS: There were no significant differences between the groups in terms of the passive resting force. The isometric force amplitude in the endocarditis group, however, was significantly lower than in the nonendocarditis group (p=0.001). In the endocarditis group, the calculated active force, defined as the isometric force amplitude minus the resting force, was significantly lower (p<0.0001) and the resting force/active force ratio was significantly higher (p<0.0001). Using linear regression to describe the function between resting force and active force, we identified a significant difference in slope (p<0.0001), with lower values found in the endocarditis group. CONCLUSION: Our data suggest that the force-generating capacity of atrial myocardium is significantly reduced in patients with IE. In these patients, an elevated resting force is required to achieve a given force amplitude. It remains unclear, however, whether this is due to calcium desensitization of the contractile apparatus, presence of myocardial edema, fibrotic remodeling, disruption of contractile units, or other mechanisms.

Protective regulation of the ACE2/ACE gene expression by estrogen in human atrial tissue from elderly men.

Data from animal experiments and clinical investigations suggest that components of the renin-angiotensin system are markedly affected by sex hormones. However, whether estrogen affects human atrial myocardium has not been investigated yet. In this study, we determined the effects of estrogen on key components of atrial renin-angiotensin system: angiotensin-converting enzyme, responsible for generation of angiotensin II and angiotensin-converting enzyme 2, counteracting majority of AngII effects, and different renin-angiotensin system receptors, AT1R, AT2R, and MAS. First, the expression levels of estrogen receptors mRNA were determined in right atrial appendages obtained from patients undergoing heart surgery. The amounts of estrogen receptor α and estrogen receptor ß mRNA were similar between women ( n = 14) and men ( n = 10). Atrial tissue slices (350 µm) were prepared from male donors which were exposed to estrogen (1-100 nM; n = 21) or stimulated at 4 Hz for 24 h in the presence or absence of 100 nM estrogen ( n = 16), respectively. The administration of estrogen did not change mRNA levels of estrogen receptors, but activated MAP kinases, Erk1/2. Furthermore, estrogen increased the amounts of angiotensin-converting enzyme 2-mRNA (1.89 ± 0.23; P < 0.05) but reduced that of angiotensin-converting enzyme-mRNA (0.78 ± 0.07, P < 0.05). In addition, the transcript levels of AT2R and MAS were upregulated by estrogen. Pacing of tissue slices significantly increased the angiotensin-converting enzyme/angiotensin-converting enzyme 2 ratio at both the mRNA and protein level. During pacing, administration of estrogen substantially lowered the angiotensin-converting enzyme/angiotensin-converting enzyme 2 ratio at the transcript (0.92 ± 0.21 vs. 2.12 ± 0.27 at 4 Hz) and protein level (0.94 ± 0.20 vs. 2.14 ± 0.3 at 4 Hz). Moreover, estrogen elicited anti-inflammatory and anti-oxidative effects on renin-angiotensin system-associated downstream effectors such as pro-oxidative LOX-1 and pro-inflammatory ICAM-1. An antagonist of estrogen receptor α reversed these anti-inflammatory and anti-oxidative effects of estrogen significantly. Overall, our results demonstrated that estrogen modifies the local renin-angiotensin system homeostasis and achieves protective effects in atrial myocardium from elderly men. Impact statement The present study demonstrates that estrogen affects the human atrial myocardium and mediates protective actions through estrogen receptors-(ER) dependent signaling. Estrogen substantially modulates the local RAS via downregulation of ACE and simultaneous upregulation of ACE2, AT2R and MAS expression levels. This is indicative of a shift of the classical RAS/ACE axis to the alternative, protective RAS/ACE2 axis. In support of this view, estrogen attenuated the expression of RAS-associated downstream effectors, LOX-1, and ICAM-1. A specific antagonist of ERα reversed the anti-inflammatory and anti-oxidative effects of estrogen in paced and non-paced atrial tissue slices. In summary, our data demonstrate the existence of protective effects of estrogen in atrial tissue from elderly men which are at least in part, mediated by the regulation of local RAS homeostasis.

The Contractility of Isolated Rat Atrial Tissue during Hypoxia is Better Preserved in a High- or Zero-Glucose Environment than in a Normal Glucose Environment.

AIM: Hyperglycemia is known to be associated with an increase in mortality in myocardial infarction and intensive care patients despite the fact that glucose metabolism plays a central role in myocardial protection. We studied the effect of different glucose levels (22 mM L(-1); 5.5 mM L(-1); and 0 mM L(-1)) on the contractile reserve of isolated rat atrial myocardium during and after hypoxia. METHODS: We observed the contraction of isolated rat atrium strips caused by electrical-field stimulation in a modified Krebs-Henseleit Buffer (KHB) organ bath oxygenated with 95% O2 + 5% CO2 at 37°C. We applied two periods of hypoxia and two periods of reoxygenation. Three glucose concentrations were used in the buffer to study the effect of glucose (high- n=6; normal- n=7; and zero-glucose n=6). The effect of isoproterenol 1 µM L(-1) was tested during the second ischemic period. RESULTS: The main finding was that both a zero-glucose (27.8 ± 5.9 vs. 14.7 ± 3 % of baseline tension) and a high-glucose environment (38.5 ± 14 vs. 14.7 ± 3 % of baseline tension) had a positive effect in terms of better contractility than the normal-glucose buffer during both the first (p=0.00062) and the second ischemic period (31.2 ± 5.9 % zero-glucose vs. 14.7 ± 4.2 normal-glucose vs. 35.3 ± 15.9% high-glucose p=0.0038). CONCLUSION: Both zero-glucose and high-glucose environments resulted in a better contractile reserve in isolated rat atrial myocardium during hypoxia than in a normal one. The exact clinical relevance of this observation is, at present, unclear.

EFFECTS OF FUROSEMIDE ON ACTION POTENTIAL AND CONTRACTILE FORCE OF ISOLATED TOAD ATRlAL MYOCARDIUM / 中国药理学通报

Using floating microelectrode, the effects of furosemide on action potential and contractile force were studied in isolated toad atrial myocardium. Furosemide increased the force of contraction of toad right atrial myocardium, amplitude and dV/dtmax of action potential, and prolonged action potential duration at 50% repolari-zation (APD50), but the APD25, APD90 and sinus cycle length ( SCL) were not influenced. The positive intropic effect of furosemide could be blocked by Verapamil. These results indicated that furosemide could promote the Ca++ inward current.

THE OBSERVATION OF ULTRASTRUCTURAL CHANGE IN ATRIAL MYOCARDIUM BIOPSY FROM VENTRICULAR SEPTAL DEFECT WITH PULMONARY HYPERTENSION / 西安交通大学学报(医学版)

The electromicroscopic observation of atrialbiopsy was carried out in 10 patients with ventric-ular septal defect (VSD) and middle, severe pul-monary hypertension (PH). The observation sug-gests that there are myofibrillar lysis to disappearwith various degrees, dilated rough endoplasmreticulum and the increase in lipofuscin granulesand lipid droplets; mitochondral hyperplasia, theirsize and shape being different, disorganizing of mi-tochondria, disintegration of cristae, mitochondralretrograde degenration and decreased matrix elec-tron density. The dilated intercalated discs and in-crease in myocardial fibrous tissue were found inpart of patients. These structural changes areprobably due to chronic myocardial ischemia.