scholarly journals Phorbol ester and endothelin-1 alter functional expression of Na+/Ca2+ exchange, K+, and Ca2+ currents in cultured neonatal rat myocytes

2011 ◽  
Vol 300 (2) ◽  
pp. H617-H626 ◽  
Author(s):  
José L. Puglisi ◽  
Weilong Yuan ◽  
Valeriy Timofeyev ◽  
Richard E. Myers ◽  
Nipavan Chiamvimonvat ◽  
...  
Keyword(s):  
Heart Failure ◽  
Ventricular Myocytes ◽  
Ionic Currents ◽  
Functional Expression ◽  
Neonatal Rat ◽  
Delayed Rectifier ◽  
Electrophysiological Properties ◽  
Endothelin 1 ◽  
Cellular Hypertrophy ◽  
Myocyte Function

Endothelin-1 (ET-1) and activation of protein kinase C (PKC) have been implicated in alterations of myocyte function in cardiac hypertrophy and heart failure. Changes in cellular Ca2+ handling and electrophysiological properties also occur in these states and may contribute to mechanical dysfunction and arrhythmias. While ET-1 or PKC stimulation induces cellular hypertrophy in cultured neonatal rat ventricular myocytes (NRVMs), a system widely used in studies of hypertrophic signaling, there is little data about electrophysiological changes. Here we studied the effects of ET-1 (100 nM) or the PKC activator phorbol 12-myristate 13-acetate (PMA, 1 μM) on ionic currents in NRVMs. The acute effects of PMA or ET-1 (≤30 min) were small or insignificant. However, PMA or ET-1 exposure for 48–72 h increased cell capacitance by 100 or 25%, respectively, indicating cellular hypertrophy. ET-1 also slightly increased Ca2+ current density (T and L type). Na+/Ca2+ exchange current was increased by chronic pretreatment with either PMA or ET-1. In contrast, transient outward and delayed rectifier K+ currents were strongly downregulated by PMA or ET-1 pretreatment. Inward rectifier K+ current tended toward a decrease at larger negative potential, but time-independent outward K+ current was unaltered by either treatment. The enhanced inward and reduced outward currents also result in action potential prolongation after PMA or ET-1 pretreatment. We conclude that chronic PMA or ET-1 exposure in cultured NRVMs causes altered functional expression of cardiac ion currents, which mimic electrophysiological changes seen in whole animal and human hypertrophy and heart failure.

Cardiac mitofusin-1 is declined in non-responding patients with idiopathic dilated cardiomyopathy

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
Y Hsiao ◽  
I Shimizu ◽  
T Wakasugi ◽  
S Jiao ◽  
T Watanabe ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Heart Failure ◽  
Ventricular Myocytes ◽  
Severe Heart Failure ◽  
Left Ventricular ◽  
Neonatal Rat ◽  
Heart Failure Patients ◽  
Underlying Mechanisms ◽  
Neonatal Rat Ventricular Myocytes ◽  
Mitofusin 1

Abstract Background/Introduction Mitochondria are dynamic regulators of cellular metabolism and homeostasis. The dysfunction of mitochondria has long been considered a major contributor to aging and age-related diseases. The prognosis of severe heart failure is still unacceptably poor and it is urgent to establish new therapies for this critical condition. Some patients with heart failure do not respond to established multidisciplinary treatment and they are classified as “non-responders”. The outcome is especially poor for non-responders, and underlying mechanisms are largely unknown. Purpose Studies indicate mitochondrial dysfunction has causal roles for metabolic remodeling in the failing heart, but underlying mechanisms remain to be explored. This study tried to elucidate the role of Mitofusin-1 in a failing heart. Methods We examined twenty-two heart failure patients who underwent endomyocardial biopsy of intraventricular septum. Patients were classified as non-responders when their left-ventricular (LV) ejection fraction did not show more than 10% improvement at remote phase after biopsy. Fourteen patients were classified as responders, and eight as non-responders. Electron microscopy, quantitative PCR, and immunofluorescence studies were performed to explore the biological processes or molecules involved in failure to respond. In addition to studies with cardiac tissue specific knockout mice, we also conducted functional in-vitro studies with neonatal rat ventricular myocytes. Results Twenty-two patients with IDCM who underwent endomyocardial biopsy were enrolled in this study, including 14 responders and 8 non-responders. Transmission electron microscopy (EM) showed a significant reduction in mitochondrial size in cardiomyocytes of non-responders compared to responders. Quantitative PCR revealed that transcript of mitochondrial fusion protein, Mitofusin-1, was significantly reduced in non-responders. Studies with neonatal rat ventricular myocytes (NRVMs) indicated that the beta-1 adrenergic receptor-mediated signaling pathway negatively regulates Mitofusin-1 expression. Suppression of Mitofusin-1 resulted in a significant reduction in mitochondrial respiration of NRVMs. We generated left ventricular pressure overload model with thoracic aortic constriction (TAC) in cardiac specific Mitofusin-1 knockout model (c-Mfn1 KO). Systolic function was reduced in c-Mfn1 KO mice, and EM study showed an increase in dysfunctional mitochondria in the KO group subjected to TAC. Conclusions Mitofusin-1 becomes a biomarker for non-responders with heart failure. In addition, our results suggest that therapies targeting mitochondrial dynamics and homeostasis would become next generation therapy for severe heart failure patients. Funding Acknowledgement Type of funding source: None

scholarly journals The Ku Protein Complex Interacts with YY1, Is Up-Regulated in Human Heart Failure, and Represses α Myosin Heavy-Chain Gene Expression

2004 ◽  
Vol 24 (19) ◽  
pp. 8705-8715 ◽  
Author(s):  
Carmen C. Sucharov ◽  
Steve M. Helmke ◽  
Stephen J. Langer ◽  
M. Benjamin Perryman ◽  
Michael Bristow ◽  
...  
Keyword(s):  
Heart Failure ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Human Heart ◽  
Ventricular Myocytes ◽  
Major Effect ◽  
Neonatal Rat ◽  
Chain Gene ◽  
Human Heart Failure ◽  
Peptide Mass

ABSTRACT Human heart failure is accompanied by repression of genes such as α myosin heavy chain (αMyHC) and SERCA2A and the induction of fetal genes such as βMyHC and atrial natriuretic factor. It seems likely that changes in MyHC isoforms contribute to the poor contractility seen in heart failure, because small changes in isoform composition can have a major effect on the contractility of cardiac myocytes and the heart. Our laboratory has recently shown that YY1 protein levels are increased in human heart failure and that YY1 represses the activity of the human αMyHC promoter. We have now identified a region of the αMyHC promoter that binds a factor whose expression is increased sixfold in failing human hearts. Through peptide mass spectrometry, we identified this binding activity to be a heterodimer of Ku70 and Ku80. Expression of Ku represses the human αMyHC promoter in neonatal rat ventricular myocytes. Moreover, overexpression of Ku70/80 decreases αMyHC mRNA expression and increases skeletal α-actin. Interestingly, YY1 interacts with Ku70 and Ku80 in HeLa cells. Together, YY1, Ku70, and Ku80 repress the αMyHC promoter to an extent that is greater than that with YY1 or Ku70/80 alone. Our results suggest that Ku is an important factor in the repression of the human αMyHC promoter during heart failure.

Abstract 208: Mitochondrial-targeted Grk2 Increases Superoxide Formation And Impairs Cardiomyocyte Respiratory Reserve Capacity

2014 ◽  
Vol 115 (suppl_1) ◽  
Author(s):  
Priscila Y Sato ◽  
J K Chuprun ◽  
Jessica Ibetti ◽  
John W Elrod ◽  
Walter J Koch
Keyword(s):  
Heart Failure ◽  
Ventricular Myocytes ◽  
Permeability Transition ◽  
Fold Increase ◽  
Confocal Imaging ◽  
Neonatal Rat ◽  
Redox Stress ◽  
Mitochondrial Oxidative Stress ◽  
Neonatal Rat Ventricular Myocytes ◽  
Cellular Dysfunction

β-adrenergic receptors (βARs) are powerful regulators of cardiovascular function and are impaired in heart failure (HF). Signal transduction of βARs is canonically shut down by phosphorylation via G protein-coupled receptor kinase 2 (GRK2) and the subsequent binding of β-arrestins. This process of receptor desensitization is enhanced in HF via the up-regulation of GRK2 and contributes to disease progression. We have recently reported non-canonical actions of GRK2, which contribute to the development of HF independent of βAR desensitization. We have previously shown that GRK2 can act as a pro-death kinase in cardiomyocytes bytranslocating to mitochondria and activating mitochondria permeability transition. This study was designed to gain more understanding of the mitochondrial function of GRK2. We isolated adult cardiomyocytes from cardiac-specific transgenic mice overexpressing GRK2 at levels found in human HF (TgGRK2), and examined superoxide production using the redox sensitive reporter MitoSox Red. Confocal imaging revealed a 4.6 fold increase in superoxide levels in cardiomyocytes overexpressing Grk2 as compared to non-transgenic (NLC) cardiomyocytes (corrected total cell fluorescence 11.59±1.06, TgGRK2 (n= 3 hearts, 88 cells) vs 2.54±0.02 NLC (n=3 hearts, 52 cells), (p<0.001). This indicates that the chronic elevation of GRK2 induces mitochondrial oxidative stress priming the myocyte for enhanced injury. To further explore the mitochondrial actions of GRK2 and consequences of redox stress we examined oxidative phosphorylation by performing oxygen consumption measurements in neonatal rat ventricular myocytes overexpressing GRK2 or GFP-expressing control myocytes. Seahorse analysis showed that cells overexpressing GRK2 have a significant decrease in spare respiratory capacity indicating that cells with elevated GRK2 levels have an impaired capacity to generated ATP during times of stress. Further studies with mutants that limit GRK2 kinase activity or mitochondrial localization demonstrate that mitochondrial GRK2 may be a significant contributor to cellular dysfunction as seen in heart failure.

Abstract 15280: Comparisons of Action Potentials and Ionic Currents Between Neonatal Rat Ventricular Myocytes and Adult Zebrafish Ventricular Myocytes

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Adonis Z Wu ◽  
Shien-Fong Lin ◽  
Sheng-Nan Wu
Keyword(s):  
Electrical Properties ◽  
Ventricular Myocytes ◽  
Ionic Currents ◽  
Firing Frequency ◽  
Neonatal Rat ◽  
Adult Zebrafish ◽  
Patch Clamp Technique ◽  
Action Current ◽  
Rat Ventricular Myocytes ◽  
Neonatal Rat Ventricular Myocytes

Introduction: Zebrafish heart is established as a model to investigate cardiac electrical abnormalities. However, electrical properties of adult zebrafish cardiomyocytes are not sufficiently characterized. Hypothesis: In this study, by comparing the electrical properties between neonatal rat ventricular myocytes (NRVMs) and adult zebrafish ventricular myocytes (AZVMs), we intended to characterize the action potential (AP), action current (AC) and the properties of Na + current ( I Na ) in AZVMs. Methods: We used patch-clamp technique to characterize the electrical properties, including AP, AC and I Na , in cultured NRVMs and freshly isolated AZVMs. Results: NVRMs showed larger AP amplitude (119±6 vs. 79±4mV, p<.05) but shorter AP duration (APD 90 , 136±11 vs. 213±19 ms, p<.05) than those of AZVMs. The AP duration exhibited marked frequency-dependent alterations in AZVMs. Under the slow pacing rate, early after-depolarizations (EAD) emerged under slow pacing rate with 0.05 Hz. In cell-attached voltage-clamp recordings made from AZVMs, ACs could be elicited by +10 mV steps. As the depolarization step increased to +70 mV, the latency for appearance of ACs was progressively reduced from >123 ms to 9.8 ms. The presence of spontaneous ACs was monitored in spontaneously beating NRVMs and AZVMs. The AC amplitude in NRVMs was larger compared to that in AZVMs (17.3±2.1 vs. 11.6±1.1 pA, p<.05), although firing frequency of AC in NRVMs is higher than in AZVMs (1.13±0.09 vs. 0.38±0.03 Hz, p<.05). The lowering effect of ranolazine, a I Na antagonist, on firing frequency was significantly larger in NRVMs (1.13±0.09 to 0.31±0.02 Hz, p<.05) than in AZVMs (0.38±0.03 to 0.27±0.02 Hz). There was a hyperpolarizing shift of peak I Na in AZVM compared to NRVM. Conclusions: Our results demonstrated major differences in the cellular electrical behavior between AZVMs and NRVMs.

scholarly journals Complex electrophysiological remodeling in postinfarction ischemic heart failure

2018 ◽  
Vol 115 (13) ◽  
pp. E3036-E3044 ◽  
Author(s):  
Bence Hegyi ◽  
Julie Bossuyt ◽  
Leigh G. Griffiths ◽  
Rafael Shimkunas ◽  
Zana Coulibaly ◽  
...  
Keyword(s):  
Heart Failure ◽  
Single Channel ◽  
Ionic Currents ◽  
Border Zone ◽  
Delayed Rectifier ◽  
Large Animal ◽  
Current Profile ◽  
Large Animal Models ◽  
Remote Zone ◽  
Arrhythmogenic Substrate

Heart failure (HF) following myocardial infarction (MI) is associated with high incidence of cardiac arrhythmias. Development of therapeutic strategy requires detailed understanding of electrophysiological remodeling. However, changes of ionic currents in ischemic HF remain incompletely understood, especially in translational large-animal models. Here, we systematically measure the major ionic currents in ventricular myocytes from the infarct border and remote zones in a porcine model of post-MI HF. We recorded eight ionic currents during the cell’s action potential (AP) under physiologically relevant conditions using selfAP-clamp sequential dissection. Compared with healthy controls, HF-remote zone myocytes exhibited increased late Na+ current, Ca2+-activated K+ current, Ca2+-activated Cl− current, decreased rapid delayed rectifier K+ current, and altered Na+/Ca2+ exchange current profile. In HF-border zone myocytes, the above changes also occurred but with additional decrease of L-type Ca2+ current, decrease of inward rectifier K+ current, and Ca2+ release-dependent delayed after-depolarizations. Our data reveal that the changes in any individual current are relatively small, but the integrated impacts shift the balance between the inward and outward currents to shorten AP in the border zone but prolong AP in the remote zone. This differential remodeling in post-MI HF increases the inhomogeneity of AP repolarization, which may enhance the arrhythmogenic substrate. Our comprehensive findings provide a mechanistic framework for understanding why single-channel blockers may fail to suppress arrhythmias, and highlight the need to consider the rich tableau and integration of many ionic currents in designing therapeutic strategies for treating arrhythmias in HF.

Abstract 356: KChIP2 Mediates Ion Channel Dysregulation by Novel Transcriptional Regulation of miR-34s

2014 ◽  
Vol 115 (suppl_1) ◽  
Author(s):  
Drew Nassal ◽  
Haiyan Liu ◽  
Xiaoping Wan ◽  
Angelina Ramirez-Navarro ◽  
Eckhard Ficker ◽  
...  
Keyword(s):  
Heart Failure ◽  
Ion Channel ◽  
Transcriptional Control ◽  
Ventricular Myocytes ◽  
Neonatal Rat ◽  
Physical Interaction ◽  
Protein Patterns ◽  
Protein Levels ◽  
Disease States

Introduction: Cardiac ion channel dysregulation is a hallmark of heart failure. Consistently, the disease yields dramatic decline in Ito through loss in Kv4 and its auxiliary partner KChIP2. Notably, transcriptional changes in heart failure can be elicited through KChIP2 silencing without disease signaling, suggesting potential transcriptional capacity for KChIP2. Further, disparity between resulting transcript and protein patterns suggests a mechanism compatible with modified miRNA activity. Considering other members of the KChIP family behave as transcriptional repressors, we hypothesize that KChIP2 regulates discrete miRNAs which in turn regulate cardiac excitability. Methods and Results: A miRNA microarray was conducted on neonatal rat ventricular myocytes (NRVM) following in vitro silencing of KChIP2 by siRNA, identifying the miR-34 family as potential transcriptional targets of KChIP2. Regulation, confirmed by quantitative PCR, showed reduction in miR-34a/b/c when over-expressing KChIP2 and increase following silencing. Luciferase assays were performed on the cloned promoter for miR-34b/c which reinforced direct KChIP2 repression on the miR-34b/c promoter. Furthermore, chromatin immunoprecipitation followed by PCR identified physical interaction of KChIP2 to the promoter site. Previous studies show modified expression of KChIP2 can lead to changes in several ion channel subunits. Therefore, we investigated if this was the consequence of KChIP2 regulation via miR-34. miR-34a/b/c precursors were expressed in NRVM which reduced transcript levels of Nav1.5 and Navβ1, and reduced protein levels for Kv4.3. Reflecting these changes, peak INa was reduced following miR precursor treatment. NRVMs were exposed to 100 μM phenylephrine for 48 hrs, significantly reducing KChIP2, Nav1.5, Navβ1, and Kv4.3, while elevating miR-34b/c. Returning KChIP2 expression by adenovirus normalized these changes back towards baseline, implicating the physiologic relevance of this pathway. Conclusion: These observations describe a novel mechanism where KChIP2 regulates a host of cardiac genes through transcriptional control of miRNAs, potentially explaining electrical remodeling observed in disease states where KChIP2 is reduced.

scholarly journals Differential Inhibitory Actions of Multitargeted Tyrosine Kinase Inhibitors on Different Ionic Current Types in Cardiomyocytes

2020 ◽  
Vol 21 (5) ◽  
pp. 1672 ◽  
Author(s):  
Wei-Ting Chang ◽  
Ping-Yen Liu ◽  
Kaisen Lee ◽  
Yin-Hsun Feng ◽  
Sheng-Nan Wu
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Kinase Inhibitors ◽  
Kinase Inhibitors ◽  
Ionic Current ◽  
Small Animal ◽  
Ionic Currents ◽  
Neonatal Rat ◽  
Delayed Rectifier ◽  
Qtc Prolongation ◽  
The Impact

Lapatinib (LAP) and sorafenib (SOR) are multitargeted tyrosine kinase inhibitors (TKIs) with antineoplastic properties. In clinical observations, LAP and SOR may contribute to QTc prolongation, but the detailed mechanism for this has been largely unexplored. In this study, we investigated whether LAP and SOR affect the activities of membrane ion channels. Using a small animal model and primary cardiomyocytes, we studied the impact of LAP and SOR on Na+ and K+ currents. We found that LAP-induced QTc prolongation in mice was reversed by isoproterenol. LAP or SOR suppressed the amplitude of the slowly activating delayed-rectifier K+ current (IK(S)) in H9c2 cells in a time- and concentration-dependent fashion. The LAP-mediated inhibition of IK(S) was reversed by adding isoproterenol or meclofenamic acid, but not by adding diazoxide. The steady-state activation curve of IK(S) during exposure to LAP or SOR was shifted toward a less negative potential, with no change in the gating charge required to activate the current. LAP shortened the recovery from IK(S) deactivation. As rapid repetitive stimuli, the IK(S) amplitude decreased; however; the LAP-induced inhibition of IK(S) remained effective. LAP or SOR alone also suppressed inwardly rectifying K+ and voltage-gated Na+ current in neonatal rat ventricular myocytes. The inhibition of ionic currents during exposure to TKIs could be an important mechanism underlying changes in QTc intervals.

scholarly journals Balance Between Rapid Delayed Rectifier K + Current and Late Na + Current on Ventricular Repolarization

2020 ◽  
Vol 13 (4) ◽  
Author(s):  
Bence Hegyi ◽  
Ye Chen-Izu ◽  
Leighton T. Izu ◽  
Sridharan Rajamani ◽  
Luiz Belardinelli ◽  
...  
Keyword(s):  
Heart Failure ◽  
Long Qt Syndrome ◽  
Therapeutic Potential ◽  
Heart Diseases ◽  
Ionic Currents ◽  
Close Correlation ◽  
Delayed Rectifier ◽  
Long Qt ◽  
Comparable Amount ◽  
Qt Syndrome

Background: Rapid delayed rectifier K + current (I Kr ) and late Na + current (I NaL ) significantly shape the cardiac action potential (AP). Changes in their magnitudes can cause either long or short QT syndromes associated with malignant ventricular arrhythmias and sudden cardiac death. Methods: Physiological self AP-clamp was used to measure I NaL and I Kr during the AP in rabbit and porcine ventricular cardiomyocytes to test our hypothesis that the balance between I Kr and I NaL affects repolarization stability in health and disease conditions. Results: We found comparable amount of net charge carried by I Kr and I NaL during the physiological AP, suggesting that outward K + current via I Kr and inward Na + current via I NaL are in balance during physiological repolarization. Remarkably, I Kr and I NaL integrals in each control myocyte were highly correlated in both healthy rabbit and pig myocytes, despite high overall cell-to-cell variability. This close correlation was lost in heart failure myocytes from both species. Pretreatment with E-4031 to block I Kr (mimicking long QT syndrome 2) or with sea anemone toxin II to impair Na + channel inactivation (mimicking long QT syndrome 3) prolonged AP duration (APD); however, using GS-967 to inhibit I NaL sufficiently restored APD to control in both cases. Importantly, I NaL inhibition significantly reduced the beat-to-beat and short-term variabilities of APD. Moreover, I NaL inhibition also restored APD and repolarization stability in heart failure. Conversely, pretreatment with GS-967 shortened APD (mimicking short QT syndrome), and E-4031 reverted APD shortening. Furthermore, the amplitude of AP alternans occurring at high pacing frequency was decreased by I NaL inhibition, increased by I Kr inhibition, and restored by combined I NaL and I Kr inhibitions. Conclusions: Our data demonstrate that I Kr and I NaL are counterbalancing currents during the physiological ventricular AP and their integrals covary in individual myocytes. Targeting these ionic currents to normalize their balance may have significant therapeutic potential in heart diseases with repolarization abnormalities. Visual Overview: A visual overview is available for this article.

scholarly journals Cardiomyocyte functional screening: interrogating comparative electrophysiology of high-throughput model cell systems

2019 ◽  
Vol 317 (6) ◽  
pp. C1256-C1267 ◽  
Author(s):  
Simon P. Wells ◽  
Helen M. Waddell ◽  
Choon Boon Sim ◽  
Shiang Y. Lim ◽  
Gabriel B. Bernasochi ◽  
...  
Keyword(s):  
Conduction Velocity ◽  
High Throughput ◽  
Microelectrode Array ◽  
Ventricular Myocytes ◽  
Field Potential ◽  
Induced Pluripotent Stem Cell ◽  
Neonatal Rat ◽  
Functional Screening ◽  
Electrophysiological Properties

Cardiac arrhythmias of both atrial and ventricular origin are an important feature of cardiovascular disease. Novel antiarrhythmic therapies are required to overcome current drug limitations related to effectiveness and pro-arrhythmia risk in some contexts. Cardiomyocyte culture models provide a high-throughput platform for screening antiarrhythmic compounds, but comparative information about electrophysiological properties of commonly used types of cardiomyocyte preparations is lacking. Standardization of cultured cardiomyocyte microelectrode array (MEA) experimentation is required for its application as a high-throughput platform for antiarrhythmic drug development. The aim of this study was to directly compare the electrophysiological properties and responses to isoproterenol of three commonly used cardiac cultures. Neonatal rat ventricular myocytes (NRVMs), immortalized atrial HL-1 cells, and custom-generated human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were cultured on microelectrode arrays for 48–120 h. Extracellular field potentials were recorded, and conduction velocity was mapped in the presence/absence of the β-adrenoceptor agonist isoproterenol (1 µM). Field potential amplitude and conduction velocity were greatest in NRVMs and did not differ in cardiomyocytes isolated from male/female hearts. Both NRVMs and hiPSC-CMs exhibited longer field potential durations with rate dependence and were responsive to isoproterenol. In contrast, HL-1 cells exhibited slower conduction and shorter field potential durations and did not respond to 1 µM isoproterenol. This is the first study to compare the intrinsic electrophysiologic properties of cultured cardiomyocyte preparations commonly used for in vitro electrophysiology assessment. These findings offer important comparative data to inform methodological approaches in the use of MEA and other techniques relating to cardiomyocyte functional screening investigations of particular relevance to arrhythmogenesis.

Increased endothelin-1 and endothelin receptor expression in myocytes of ischemic and reperfused rat hearts and ventricular myocytes exposed to ischemic conditions and its inhibition by nitric oxide generation

2003 ◽  
Vol 81 (2) ◽  
pp. 105-113 ◽  
Author(s):  
Xiaohong Tracey Gan ◽  
Subrata Chakrabarti ◽  
Morris Karmazyn
Keyword(s):  
Nitric Oxide ◽  
Mrna Expression ◽  
Ventricular Myocytes ◽  
Receptor Expression ◽  
Neonatal Rat ◽  
No Donor ◽  
Myocardial Ischemia And Reperfusion ◽  
Endothelin 1 ◽  
Hypoxic Conditions ◽  
Rat Hearts

Endothelin-1 (ET-1) and nitric oxide (NO) exert opposite effects in the cardiovascular system, and there is evidence that the NO counters the potential deleterious effects of ET-1. We investigated whether NO affects the increased mRNA expression of ET-1 and endothelin receptors induced by (i) 30 min of ischemia with or without 30 min reperfusion in myocytes from isolated rat hearts or (ii) ischemic conditions (acidosis or hypoxia) in cultured rat neonatal ventricular myocytes. Ischemia with or without reperfusion produced more than a twofold increase in mRNA expression of ET-1 as well as the ETAand ETBreceptor (P < 0.05), although these effects were completely blocked by the NO donor 3-morpholinosydnonimine (SIN-1; 1 μM). To assess the possible factors regulating ET expression, myocytes were exposed to acidosis (pH 6.8–6.2) or to hypoxic conditions in an anaerobic chamber for 24 h in the presence or absence of SIN-1. At all acidic pHs, ET-1 and ETAreceptor mRNA expression was significantly (P < 0.05) elevated approximately threefold, although the magnitude of elevation was independent of the degree of acidosis. These effects were completely prevented by SIN-1. ETBreceptor expression was unaffected by acidosis. Hypoxia increased ET-1 as well as ETAand ETBreceptor expression threefold (P < 0.05), although this was unaffected by SIN-1. Our results demonstrate that myocardial ischemia and reperfusion upregulate the ET system, which is inhibited by NO. Although increased expression of the ET system can be mimicked by both acidosis and hypoxia, only the effects of the former are NO sensitive. NO may serve an endogenous inhibitory factor which regulates the expression of the ET system under pathological conditions.Key words: ET-1, ET receptors, NO, neonatal rat ventricular myocytes, hypoxia, acidosis.

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