tetrodotoxin and Myocardial-Ischemia

Topics: Action Potentials; Animals; Calcium Channel Blockers; Death, Sudden, Cardiac; Electrocardiography; Gallopamil; Heart Conduction System; Humans; Models, Biological; Myocardial Ischemia; Rabbits; Sodium Channel Blockers; Tachycardia, Ventricular; Tetrodotoxin; Ventricular Fibrillation

Topics: Animals; Arrhythmias, Cardiac; Heart Transplantation; Humans; Myocardial Infarction; Myocardial Ischemia; Rats; Sodium Channels; Sympathetic Nervous System; Tetrodotoxin

The increases in persistent sodium currents (I (Na.P)) and Na(+)/H(+) exchange (NHE) causes intracellular Ca(2+) overload. The objective of this study was to determine the contribution of I (Na.P) and NHE on the hypoxia- or acute ischemia-induced increase in the reverse Na(+)/Ca(2+) exchange current (HIR- or AIR-I (NCX)). I (Na.P) and I (NCX) in rabbit ventricular myocytes were recorded during hypoxia or acute ischemia, combination of acidosis (pH values were 6.0 intracellularly and 6.8 extracellularly) and hypoxia, using whole-cell patch-clamp techniques. The results indicate that (1) under hypoxic condition, the augmentation of both HIR-I (NCX) and I (Na.P) was inhibited by TTX (2 to 8 μM) in a concentration-dependent manner. The inhibitions of I (Na,P) and HIR-I (NCX) reached maximum in the presence of either 4 μM TTX or 10 μM KR-32568 (a NHE inhibitor), respectively. The maximal inhibitions of HIR-I (NCX) by 4 μM TTX and 10 μM KR-32568 were 72.54% and 16.89%, respectively. (2) Administration of 2 μM TTX and 10 μM KR-32568 in either order in the same cells decreased HIR-I (NCX) by 64.83% and 16.94%, respectively. (3) I (Na.P) and the reverse I (NCX) were augmented during acute ischemia. TTX (4 μM) and KR-32568 (10 μM) reduced AIR-I (NCX) by 73.39% and 24.13%, respectively. (4) Under normoxic condition, veratridine (20 μM) significantly increased I (Na.P) and the reverse I (NCX), which was reversed by 4 μM TTX. In conclusion, during hypoxia or acute ischemia, both increased I (Na.P) and NHE contribute to the HIR- or AIR-I (NCX) with the former playing a major role comparing with the latter.

Topics: Animals; Cell Hypoxia; Dose-Response Relationship, Drug; Female; Guanidines; Heart Ventricles; Male; Myocardial Ischemia; Myocytes, Cardiac; Patch-Clamp Techniques; Rabbits; Sodium-Calcium Exchanger; Sodium-Hydrogen Exchangers; Tetrodotoxin

Ranolazine (Ran), an antianginal agent, inhibits late Na(+) current. The purpose of this study was to determine whether there was an added benefit of adding Ran to cardioplegia (CP) in a model of global ischemia/reperfusion.. Isolated rat hearts were Langendorff-perfused and exposed to 40-minute normothermic, cardioplegic global ischemia and 30 minutes of reperfusion. Before ischemia and during reperfusion, hearts were treated with no drug (control) or with the late Na(+) current inhibitors Ran (5 micromol/L) or tetrodotoxin (1 micromol/L). Ischemic cardioplegic arrest led to an increase of left ventricular end-diastolic pressure (LVEDP) by > or =20 mm Hg (ie, cardiac contracture). Ten out of 11 hearts treated with CP alone developed contracture, whereas 6 out of 11 hearts treated with CP plus Ran developed contracture. Ran added to CP reduced LVEDP at the end of ischemia from 41+/-5 mm Hg in CP alone to 26+/-3 mm Hg in CP plus Ran (P=0.024). Area under the curve for LVEDP during the entire ischemic period was also smaller in CP plus Ran versus CP alone. The percent increase (from baseline) of LVEDP measured at the end of 30-minute reperfusion was smaller for CP plus Ran (66+/-18%) versus CP alone (287+/-90%; P=0.035). The area under the curve for LVEDP during reperfusion was smaller in CP plus Ran versus CP alone. Tetrodotoxin (1 micromol/L) also reduced cardiac contracture during ischemia/reperfusion, compared to CP alone.. Our results suggest that Ran may have therapeutic potential as an adjunct to CP and further support a protective role of Na(+) current inhibition during ischemia/reperfusion.

Topics: Acetanilides; Angina Pectoris; Animals; Diastole; Female; Heart Arrest, Induced; Myocardial Contraction; Myocardial Ischemia; Piperazines; Ranolazine; Rats; Rats, Sprague-Dawley; Sodium; Tetrodotoxin

We describe the discovery of the first selective, potent, and voltage-dependent inhibitor of the late current mediated by the cardiac sodium channel Na V1.5. The compound 3,4-dihydro- N-[(2 S)-3-[(2-methoxyphenyl)thio]-2-methylpropyl]-2 H-(3 R)-1,5-benzoxathiepin-3-amine, 2a (F 15845), was identified from a novel family of 3-amino-1,5-benzoxathiepine derivatives. The late sodium current inhibition and antiischemic effects of 2a were studied in various models in vitro and in vivo. In a rabbit model of ischemia-reperfusion, 2a exhibited more potent antiischemic effects than reference compounds KC 12291, ranolazine, and ivabradine. Thus, after a single administration, 2a almost abolished ST segment elevation in response to a transient coronary occlusion. Further, the antiischemic activity of 2a is maintained over a wide range of doses and is not associated with any hemodynamic changes, contrary to conventional antiischemic agents. The unique pharmacological profile of 2a opens new and promising opportunities for the treatment of ischemic heart diseases.

Topics: Animals; Dose-Response Relationship, Drug; Electrophysiology; Female; Guinea Pigs; Humans; Imaging, Three-Dimensional; Male; Models, Molecular; Molecular Structure; Myocardial Ischemia; Rabbits; Rats; Rats, Wistar; Reperfusion; Sodium Channel Blockers; Structure-Activity Relationship

Possible mechanisms underlying sodium overload-induced ischemia/reperfusion injury in perfused rat hearts were examined. Massive accumulation of myocardial Na(+) occurred during ischemia, suggesting cytosolic sodium overload in cardiac cells. Treatment of the pre-ischemic heart with 0.3 micromol/l tetrodotoxin or 3 micromol/l ethyl-isopropyl amiloride enhanced post-ischemic contractile recovery (72 or 82% of initial vs 24% for untreated group), which was associated with suppression of tissue Na(+) accumulation (138 or 141% of initial vs 270% for untreated group), restoration of tissue high-energy phosphates, and preservation of the ability of mitochondria to produce ATP in the ischemic/reperfused heart. The release of cytochrome c from the ischemic heart was observed, which was blocked by treatment of the pre-ischemic heart with these agents. The improvement of post-ischemic contractile recovery by these agents was closely correlated with the ability of mitochondria to produce ATP during ischemia. To examine the effects of sodium overload on mitochondrial function, isolated mitochondria were incubated in the presence of various concentrations of Na(+). Na(+) induced mitochondrial membrane perturbations such as depolarization of the membrane potential, mitochondrial swelling, cytochrome c release from isolated mitochondria, and a reduction in oxidative phosphorylation. These events in the isolated mitochondria were not blocked by the presence of the above agents. The results suggest that cytosolic sodium overload in cardiac cells may induce deterioration of the mitochondrial function during ischemia and that this mitochondrial damage may determine post-ischemic contractile dysfunction in perfused rat hearts.

Topics: Amiloride; Animals; Anti-Arrhythmia Agents; Cytochrome c Group; In Vitro Techniques; Male; Membrane Potentials; Mitochondria; Myocardial Ischemia; Myocardial Reperfusion; Oxidative Phosphorylation; Rats; Rats, Wistar; Sodium; Tetrodotoxin

Primary cultured human coronary myocytes, derived from patients with end-stage heart failure (NYHA, classes III and IV) caused by an ischemic disease and undergoing heart transplantation, express a voltage-gated tetrodotoxin-sensitive sodium current (INa). This current has atypical electrophysiological and pharmacological properties and regulates intracellular sodium ([Na+]i) and calcium ([Ca2+]i). Our work is aimed at identifying its role and regulation of expression during pathophysiology. We currently investigate whether INa is expressed in vascular smooth muscles cells (VSMCs) isolated from either healthy or diseased (atheromatous) arteries in human and, in parallel, in pig, rabbit and rat. Cells were enzymatically isolated, primary cultured and macroscopic INa were recorded using the whole cell patch clamp technique. We found that INa is expressed in VSMCs grown from human aortic (90%; n = 48) and pulmonary (44%; n = 16) arteries and in the human aortic cell line HAVSMC (94%; n = 27). INa was also detected in pig coronary (60%; n = 25) and rabbit aortic (47%; n = 15) VSMCs, but not in rat aortic myocytes (n = 30). These different INa were activated at similar range of potentials (approximately -45 mV), had similar sensitivity to tetrodotoxin (IC50 around 5 nM) and similar density (2 to 4 pA/pF). Their expression was related to cell dedifferentiation in vitro. However, INa was observed more frequently in human myocytes derived from diseased arteries (ischemic cardiopathy) than in those derived from healthy tissues (dilated cardiopathy). In conclusion, INa may contribute to increase the basal arterial contractility and play a role in pathological situations including hypertension.

Topics: Action Potentials; Animals; Aorta; Aortic Diseases; Arterial Occlusive Diseases; Arteriosclerosis; Cardiomyopathy, Dilated; Cell Differentiation; Cells, Cultured; Coronary Artery Disease; Coronary Vessels; Disease Models, Animal; Humans; Hypertension; Ion Channel Gating; Muscle, Smooth, Vascular; Myocardial Ischemia; Patch-Clamp Techniques; Pulmonary Artery; Rabbits; Rats; Rats, Wistar; Sodium Channels; Swine; Tetrodotoxin; Vasomotor System

Contribution of sodium channels and sodium/hydrogen exchangers (NHEs) to sodium accumulation during ischemia in the ischemic/reperfused heart was examined. Ischemia increased the myocardial sodium. Reperfusion elicited a further increase in the myocardial sodium, which was associated with little recovery of the left ventricular developed pressure (LVDP) of the perfused heart. Treatment with tetrodotoxin or dimethylamirolide (DMA) dose-dependently attenuated the ischemia- and reperfusion-induced increase in myocardial sodium and enhanced the post-ischemic recovery of the LVDP. There was an inverse relationship between the increase in myocardial sodium during ischemia and the post-ischemic recovery of the LVDP.The myocardial sodium accumulation during ischemia is mainly attributed to sodium influx through sodium channels and NHEs.

Topics: Amiloride; Animals; In Vitro Techniques; Ions; Male; Myocardial Contraction; Myocardial Ischemia; Myocardium; Rats; Rats, Wistar; Sodium; Sodium Channel Blockers; Sodium Channels; Sodium-Hydrogen Exchangers; Tetrodotoxin; Ventricular Function, Left

Previous work has demonstrated that drugs which inhibit Na+ entry through voltage-sensitive Na+ channels, or via Na(+)-H+ exchange protect the heart from ischemic reperfusion damage. The purpose of our study was to determine whether these drugs in combination will have an additive protective effect in Langendorff-perfused hearts. During reperfusion following 30 min of ischemia, developed tension and resting tension were 24 +/- 3 and 162 +/- 5%, respectively, of pre-ischemic values in non-treated ischemic hearts. The administration of HOE-642 to inhibit Na+/H+ exchange increased active developed tension (DT) to 58 +/- 2% of pre-ischemic levels and decreased resting tension (RT) to 111 +/- 3% of pre-ischemic levels. The administration of tetrodotoxin (TTX) to block the Na+ channel increased DT to 56 +/- 3% of the pre-ischemic level and reduced the RT to 126 +/- 12% of the pre-ischemic level. Together, HOE-642 and TTX increased recovery of DT to 63 +/- 2% of pre-ischemic levels and improved RT to 116 +/- 4% of pre-ischemic levels after 30 min of reperfusion. All drug treatment protocols significantly lowered the creatine phosphokinase activity measured in the coronary effluent in comparison to that observed in the non-treated hearts. These data demonstrate that inhibition of Na+ entry through either Na(+)-H+ exchange or the Na+ channel protects the heart from ischemic injury, but there is no additional benefit of blocking both routes of Na+ entry simultaneously. This suggests that a threshold level of Na+i may be a critical factor in ischemic cardioprotection.

Topics: Animals; Drug Interactions; Guanidines; Heart; Male; Myocardial Ischemia; Myocardial Reperfusion Injury; Rats; Rats, Sprague-Dawley; Sodium; Sodium Channel Blockers; Sodium-Hydrogen Exchangers; Sulfones; Tetrodotoxin

Ventricular fibrillation (VF) leads to global ischemia of the heart. After 1 to 2 minutes of onset, the VF rate decreases and appears more organized. The objectives of this study were to determine the effects of no-flow global ischemia on nonlinear wave dynamics and establish the mechanism of ischemia-induced slowing of the VF rate.. Activation patterns of VF in the Langendorff-perfused rabbit heart were studied with the use of 2 protocols: (1) 15 minutes of no-flow global ischemia followed by reperfusion (n=7) and (2) decreased excitability induced by perfusion with 5 micromol/L of tetrodotoxin (TTX) followed by washout (n=3). Video imaging ( approximately 7500 pixels per frame; 240 frames per second) with a voltage-sensitive dye, ECG, and signal processing (fast Fourier transform) were used for analysis. The dominant frequency of VF decreased from 13.5+/-1.3 during control to 9.3+/-1.4 Hz at 5 minutes of global ischemia (P<0.02). The dominant frequency decreased from 13.9+/-1.1 during control to 7.0+/-0.3 Hz at 2 minutes of TTX infusion (P<0.001). The rotation period of rotors on the epicardial surface (n=27) strongly correlated with the inverse dominant frequency of the corresponding episode of VF (R2=0. 93). The core area, measured for 27 transiently appearing rotors, was 5.3+/-0.7 mm2 during control. A remarkable increase in core area was observed both during global ischemia (13.6+/-1.7 mm2; P<0.001) and TTX perfusion (16.8+/-3.6 mm2; P<0.001). Density of wave fronts decreased during both global ischemia (P<0.002) and TTX perfusion (P<0.002) compared with control.. This study suggests that rotating spiral waves are most likely the underlying mechanism of VF and contribute to its frequency content. Ischemia-induced decrease in the VF rate results from an increase in the rotation period of spiral waves that occurs secondary to an increase in their core area. Remarkably, similar findings in the TTX protocol suggest that reduced excitability during ischemia is an important underlying mechanism for the changes seen.

Topics: Animals; Electrocardiography; In Vitro Techniques; Linear Models; Myocardial Ischemia; Rabbits; Rotation; Sodium Channel Blockers; Tetrodotoxin; Ventricular Fibrillation; Video Recording

Lysophosphatidylcholine (LPC) is an amphiphilic metabolite that can be produced from membrane-phospholipids by activation of phospholipase A2 (PLA2), and it accumulates in the heart during ischemia and reperfusion. It is known that LPC is an arrhythmogenic substance. Recent studies have revealed that LPC produces mechanical and metabolic derangements in perfused working rat hearts, and Ca(2+)-overload in isolated cardiac myocytes. Thus, LPC possesses an ischemia-like effect on the heart. LPC accumulated in the myocardium activates phospholipase A2, establishing a vicious circle; i.e. LPC itself has an ability to produce another LPC. Therefore, a drug that has an anti-LPC effect would protect or improve ischemia/reperfusion damage. This article will review the effect of LPC in relation to ischemia, and consider a possibility of developing new anti-ischemic drugs on the basis of the anti-LPC action.

Topics: Adrenergic beta-Antagonists; Animals; Calcium; Cats; Dilazep; Enzyme Activation; Heart; Humans; In Vitro Techniques; Lysophosphatidylcholines; Myocardial Ischemia; Myocardial Reperfusion Injury; Myocardium; Phospholipases A; Phospholipases A2; Propranolol; Rats; Swine; Tetrodotoxin

We hypothesized that the slowly inactivating component of Na+ current, which is an integral part of the Na+ window current, is a major pathway for Na+ loading during myocardial ischemia. The putative protective effects of tetrodotoxin (TTX) and R-56865, at concentrations that selectively blocked the Na+ window current, as assessed by action potential plateau shortening without affecting maximum upstroke velocity (Vmax), were examined in isolated Langendorff-perfused guinea pig hearts subjected to 50 min of normothermic global ischemia and 60 min of reperfusion. In papillary muscles, TTX reduced action potential duration at > or = 10 nM but reduced Vmax only at > or = 1 microM. R-56865 (10 nM-10 microM) failed to affect Vmax but concentration dependently reduced action potential duration. Ischemia-induced cardiac dysfunction, including increases in left ventricular end-diastolic pressure and lactate dehydrogenase and creatine phosphokinase release at reperfusion, was attenuated by TTX and R-56865 (0.1-320 nM). Ischemic contracture (increase in left ventricular end-diastolic pressure) was abolished by drug concentrations as low as 1 nM, whereas higher concentrations (> 10 nM) of TTX and R-56865 were required to restore systolic function at reperfusion. TTX and R-56865 had little or no effect on hemodynamic variables. Evidence is provided of pronounced and direct cardioprotective effects of low concentrations of R-56865 and TTX in cardiac muscle during ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Action Potentials; Animals; Benzothiazoles; Biomechanical Phenomena; Electric Conductivity; Guinea Pigs; Heart; In Vitro Techniques; Male; Myocardial Contraction; Myocardial Ischemia; Myocardial Reperfusion; Papillary Muscles; Piperidines; Reference Values; Sodium; Tetrodotoxin; Thiazoles

The effect of chronic ischemia on the electrical properties of human cardiac tissue is not well understood.. Membrane potentials were studied using microelectrode techniques in isolated human ventricular tissues obtained from nonischemic (n = 17) or chronically ischemic (n = 7) myocardium. In normal Tyrode's solution, resting potential (Vr) was lower in ischemic (-70.1 +/- 2.12 mV) than in nonischemic muscles (-77.6 +/- 0.93 mV; mean +/- SEM; P < 0.05). In high [K]o (> 10 mM) media, Vr was of similar magnitude in both types of tissue (in 21.6 mM [K]o, Vr was -53.1 +/- 2.24 mV in nonischemic and -49.6 +/- 2.03 mV in ischemic preparations; n = 7 each; P > 0.05). Lowering [K]o caused persistent hyperpolarization in nonischemic muscles, but caused depolarization in chronically ischemic preparations (in 2.7 mM [K]o, Vr was -84.9 +/- 2.74 mV and -61.7 +/- 7.72 mV, respectively; n = 7; P < 0.05). Pinacidil (100 microM) normalized the response of chronically ischemic preparations to [K]o. Action potentials (APs) from nonischemic tissues varied in shape and could show aberrations. Epinephrine (1.5 microM) and 4-aminopyridine (3 mM) increased the AP duration, while butanedione monoxime (20 mM) and tetrodotoxin (1 microM) shortened it. In chronically ischemic muscles, the AP was characterized by the absence of a plateau and the presence of a slow phase of final repolarization.. The differential effect of low [K]o on the resting membrane potential of nonischemic and chronically ischemic tissues suggests a change in the properties or the regulation of background K+ channels during chronic ischemia.

Topics: 4-Aminopyridine; Action Potentials; Chronic Disease; Diacetyl; Epinephrine; Heart; Humans; In Vitro Techniques; Membrane Potentials; Middle Aged; Myocardial Ischemia; Potassium; Tetrodotoxin

Vascular endothelial growth factor (VEGF or vascular permeability factor), a direct-acting, endothelial cell-specific mitogen, has been suggested to be involved in development and maintenance of vasculatures in tumor neovascularization and in normal tissues. To investigate possible roles of VEGF in ischemic hearts, we studied induction of VEGF mRNA by ischemia and hypoxia using coronary artery-ligated hearts in vivo and perfused hearts and cultured myocardial cells in vitro. VEGF mRNA was potently induced by ischemia in the heart in vivo. In perfused hearts, maximum expression was rapidly induced (within 30 min) by transient reversible ischemia (5-10 min of ischemia) and lasted at least 3 h. Induction was also caused by hypoxia, which was confirmed in perfused hearts and cultured myocardial cells. These results suggest that induction of VEGF mRNA is upregulated by oxygen deprivation in the heart and that not only infarction but also chronic ischemia in the clinical setting could induce VEGF as a potent angiogenesis factor to stimulate coronary collateral formation.

Topics: Animals; Base Sequence; Blotting, Northern; Cells, Cultured; Coronary Vessels; Cycloheximide; DNA Primers; Endothelial Growth Factors; Fibroblast Growth Factor 2; Gene Expression; Heart; Lymphokines; Male; Molecular Sequence Data; Myocardial Ischemia; Myocardial Reperfusion; Myocardium; Polymerase Chain Reaction; Rats; Rats, Sprague-Dawley; RNA, Messenger; Tetrodotoxin; Time Factors; Transcription, Genetic; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors