tetrodotoxin and Heart-Arrest

Polarized arrest, induced by tetrodotoxin (TTX) at an optimal concentration of 22 micromol/L, has been shown to reduce ionic imbalance and improve myocardial preservation compared with hyperkalemic (depolarized) arrest. Additional pharmacologic manipulation of ionic changes (involving inhibition of Na+ influx by the Na+/H+ exchanger [HOE694] and Na+/K+/2Cl- cotransporter [furosemide], and calcium desensitization [BDM]) may further improve long-term preservation. In this study, we (i) established optimal concentrations of each drug, (ii) determined additive effects of optimal concentrations of each drug and (iii) compared our optimal preservation solution to an established depolarizing cardioplegia (St Thomas' Hospital solution No 2: STH2) used during long-term hypothermic storage for clinical transplantation.. The isolated working rat heart, perfused with Krebs Henseleit (KH) buffer was used; cardiac function was measured after 20 min aerobic working mode perfusion. The hearts (n=6/group) were arrested with a 2 ml infusion (for 30 sec) of the polarizing (control) solution (22 micromol/L TTX in KH) or control+drug and subjected to 5 hr or 8 hr of storage at 7.5 degrees C in the arresting solution. Postischemic function during reperfusion was measured (expressed as percentage of preischemic function).. Dose-response studies established optimal concentrations of HOE694 (10 micromol/L), furosemide (1.0 micromol/L) and BDM (30 mmol/L) in the polarizing (control) solution. Sequential addition to the control solution (Group I) of optimal concentrations of HOE694 (Group II), furosemide (Group III), and BDM (Group IV) were compared with STH2 (Group V); postischemic recovery of aortic flow was 29+/-7%, 49+/-6%*, 56+/-2%*, 76+/-3%*, and 25+/-6%, respectively (*P<0.05 vs. I and V). Creatine kinase leakage was lowest, and myocardial ATP content was highest in Group IV.. A polarizing preservation solution (KH+TTX) containing HOE694, furosemide, and BDM significantly enhanced long-term preservation compared with an optimized depolarizing solution (STH2) used clinically for long-term donor heart preservation.

Topics: Adenine Nucleotides; Animals; Bicarbonates; Calcium Chloride; Cardioplegic Solutions; Creatine Kinase; Energy Metabolism; Guanidines; Heart; Heart Arrest; Magnesium; Male; Myocardium; Organ Preservation; Potassium; Potassium Chloride; Rats; Rats, Wistar; Sodium Chloride; Sodium-Hydrogen Exchangers; Sulfones; Tetrodotoxin

In amphibians and mammals, vagal stimulation leads to the release of acetylcholine, ACh, which causes bradycardia. However, the responses to nerve stimulation are not well mimicked by exogenously applied ACh. These observations have led to the suggestion that there are subpopulations of muscarinic receptors on pacemaker cells and that during vagal stimulation neuronally released ACh caused slowing by suppressing inward current flow during diastole. After the generation of action potentials has been prevented by applying an organic calcium antagonist, vagal stimulation causes a hyperpolarization and an increase in membrane resistance: this observation suggests that the hyperpolarization results from a suppression of inward, presumably Na+, current flow. In this study we describe the effects of vagal stimulation on membrane potentials recorded from arrested and beating hearts by using a computer model. The model of Noble & Noble (Proc. R. Soc. Lond. B 222, 295 (1984)) was modified to describe the shape of amphibian pacemaker action potentials. A voltage-dependent Na conductance was included as well as two voltage-independent conductances, a background Na conductance and a background K conductance. Subsequently the hypothesis that the changes in membrane potential recorded during vagal stimulation from arrested preparations resulted from a reduction in Na conductance and this represented the sole action of vagally released. ACh, was tested. If this were so, the changes in membrane conductance that occur during vagal inhibitory junction potentials recorded from arrested preparations should produce changes in pacemaker action potentials similar to those recorded experimentally from beating preparations. This was found to be the case. Thus the analyses are consistent with the idea that vagal inhibition of pacemaker cells results solely from a suppression of the two pacemaker sodium currents.

Topics: Action Potentials; Animals; Bufo marinus; Computer Simulation; Electric Stimulation; Heart Arrest; Heart Conduction System; Membrane Potentials; Models, Cardiovascular; Potassium Channels; Sodium Channels; Tetrodotoxin; Vagus Nerve

Topics: Anesthetics; Animals; Coronary Circulation; Coronary Vessels; Halothane; Heart Arrest; In Vitro Techniques; Isoflurane; Male; Rats; Tetrodotoxin; Vascular Resistance

The heart contains superficial cardiac nerves whose effects may be modulated by pericardial fluid bathing the epicardium. We tested this hypothesis in open-chest dogs anesthetized with secobarbital. Oxygenated normal Tyrode's solution (NT) or NT containing hexamethonium, a ganglionic blocker (500 microM), or tetrodotoxin, a blocker of axonal neurotransmission (5 microM, TTX), was instilled into the pericardial cavity to superfuse the epicardium of the whole heart. During each superfusion, effective refractory period (ERP) was determined in deep intramyocardium (greater than or equal to 4 mm in depth from the epicardium) of anterior and posterior left ventricle and in the subendocardium of the right ventricle in the baseline state and during bilateral cervical vagal stimulation (VS) or ansae subclaviae stimulation (SS). Lengthening of ERP induced by VS during superfusion with NT (6.9 +/- 0.3 msec, mean +/- SEM, n = 36) was eliminated during subsequent superfusion with hexamethonium (0.9 +/- 0.5 msec, p less than 0.001). Hexamethonium also prevented sinus arrest induced by VS but did not affect shortening of ERP induced by SS (17.3 +/- 1.3 to 16.6 +/- 1.0 msec, n = 26). TTX suppressed VS-induced changes in ERP (6.3 +/- 0.3 to 1.5 +/- 0.5 msec, n = 32, p less than 0.001) and SS-induced changes in ERP (18.8 +/- 1.6 to 6.0 +/- 0.9 msec, n = 23, p less than 0.001) but did not affect changes in ERP induced by intravenous administration of norepinephrine or methacholine.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Autonomic Nervous System; Dogs; Electric Stimulation; Female; Ganglionic Blockers; Heart Arrest; Heart Conduction System; Heart Ventricles; Hemodynamics; Hexamethonium; Hexamethonium Compounds; Isotonic Solutions; Male; Methacholine Chloride; Methacholine Compounds; Norepinephrine; Perfusion; Pericardium; Refractory Period, Electrophysiological; Synaptic Transmission; Tetrodotoxin; Vagus Nerve

Basal energy requirements of polarized [tetrodotoxin (TTX), 25 microns] and depolarized [potassium (K), 20 mM] arrested hearts were studied by continuously measuring myocardial oxygen consumption (MVO2) during 60 min of normothermic arrest in isolated Langendorff-perfused rat hearts. TTX, a fast sodium channel blocker, was used to produce polarized arrest because of its specificity and reversibility. MVO2 was significantly lower in the polarized (TTX) group at all time points, a typical difference occurring 30 min after arrest (0.070 +/- 0.005 vs. 0.109 +/- 0.006 ml O2.min-1.g dry wt-1, P less than 0.001). Coronary flow was lower in the polarized group (14.3 +/- 1.4 vs. 28.4 +/- 2.2 ml.min-1.g dry wt-1, P less than 0.001, data at 30 min of arrest), but flow-restricted studies showed basal MVO2 to be independent of variation in coronary flow within this range. Recovery of function was similar in both groups. Ventricular pressure during cardiac arrest was lower in the polarized group (5.5 +/- 1.2 vs. 10.3 +/- 1.3 mmHg, P less than 0.01, data at 30 min of arrest), implying reduced myocardial wall tension and a lower intracellular calcium concentration. These results suggest that polarized arrest can decrease myocardial metabolic demands below that of depolarized arrest. A plausible mechanism is a reduction in myocardial wall tension caused by decreased calcium influx mediated by the Na-Ca exchanger.

Topics: Animals; Coronary Circulation; Energy Metabolism; Heart; Heart Arrest; Heart Rate; In Vitro Techniques; Male; Myocardium; Oxygen Consumption; Potassium; Rats; Rats, Inbred Strains; Reference Values; Tetrodotoxin

We investigated the effect of the sodium channel blocker, tetrodotoxin, in two animal models of brain pathology. In the first, an acute model, we recorded the interstitial brain potential in the striatum of rats after cardiac arrest. The time of deflection of this potential, an indication of changes in cerebral cation concentrations, was determined in control rats, and in rats pretreated with intrastriatal tetrodotoxin. In control rats a deflection of the brain potential was noted 2 min after cardiac arrest; tetrodotoxin pretreatment delayed this deflection to about 5 min. The second, a survival model, was based on the Levine preparation in rats. A combination of ischemia and hypoxia produced unilateral, cerebral infarcts, which were characterized by a decrease of brain [K+], and by increases of [Ca2+] and [Na+] and thus of the Na+:K+ ratio. Data on the cation shifts, determined by chemical assay methods, were complemented by those of more conventional methods of assessment of brain damage, such as the determination of survival, of Evans blue staining, and of brain water content. Cation shifts could be prevented locally by tetrodotoxin. In conclusion, the drug can, at least partially, prevent the detrimental effects of an ischemic insult. In addition, our results showed that protective effects observed in the acute model may sometimes offer an indication of the effects to be expected in the survival model. Furthermore, the effect of tetrodotoxin on the brain potentials in the acute model showed that its protective action in the survival model may be brought about by delaying cell depolarization and by shortening the actual duration of the depolarized state. We conclude that Na+ influx and, consequently, neurotransmission may play a crucial role in the development of cerebral damage.

Topics: Animals; Body Water; Brain; Calcium; Cations; Evans Blue; Female; Heart Arrest; Hypoxia, Brain; Ischemic Attack, Transient; Magnesium; Magnesium Chloride; Membrane Potentials; Potassium; Rats; Rats, Inbred Strains; Sodium; Tetrodotoxin

The electrical activity of the sino-atrial node was studied after the selective cannulation of its artery in the intact open-chest dog. After tetrodotoxin infusion and despite cardiac arrest, a slow rhythmic activity was recorded from the sinus epicardial electrode.

Topics: Animals; Cardiac Catheterization; Coronary Vessels; Dogs; Electrocardiography; Female; Heart Arrest; Male; Sinoatrial Node; Tetrodotoxin

Intracoronary injection of 14 mcg. of tetrodotoxin into the ischemic isolated rat heart resulted in immediate cessation of mechanical activity. Upon reperfusion with oxygenated, modified Krebs-Henseleit bicarbonate buffer in a modified Langendorff apparatus, all hearts recovered normal rate, rtythm, and contractile vigor after up to 60 minutes of ischemia. In contrast, all hearts not administered tetrodotoxin showed bradycardia, irregular rhythm, and weak contraction upon reperfusion after 30 and 45 minutes of ischemia; after 60 minutes, no mechanical activity was evident. The improved cardiac function following ischemia in the tetrodotoxin-treated hearts was associated with persistence of normal adenosine triphosphate (ATP) levels after up to 30 minutes of ischemia and normal or elevated creatine phosphate (CP) levels after up to 60 minutes of ischemia. On the other hand, ATP and CP levels progressively declined to reach 50 per cent of normal values after 30 minutes in the ischemic hearts without tetrodotoxin. These findings indicate that postarrest ATP and CP levels play an important role in myocardial recovery after ischemic arrest.

Topics: Adenosine Triphosphate; Animals; Bicarbonates; Buffers; Coronary Disease; Disease Models, Animal; Heart; Heart Arrest; Heart Conduction System; Heart Rate; Myocardium; Perfusion; Phosphocreatine; Rats; Tetrodotoxin; Time Factors

Interruption of coronary flow during cardiac surgical procedures provides a bloodless flaccid heart and allows precise and rapid correction of complex cardiac defects. However, myocardial damage occurs in direct proportion to the duration of the ischemia. As the induction of cardioplegia simulataneous with the initiation of cardiac ischemia helps to preserve cardiac energy reserves and thus myocardial integrity, the identification of a consistently reliable cardioplegic technique is desirable. Isolated perfused working rat hearts were made ischemic for one hour by aortic cross-clamping and were compared with hearts rendered cardioplegic at the onset of ischemia by the intracoronary administration of 5 ml of a hypothermic solution: 1) Krebs-Henseleit buffer, 2) Ringer's lactate, 3) tetrodotoxin, 4) potassium chloride, or 5) potassium citrate. Cardiac output, heart rate, aortic pressure and coronary flow were determined pre and post-ischemia. When compared to time-matched controls and hearts arrested with potassium or tetrodotoxin, the ischemia and ischemia-Ringer's lactate groups showed significant post cross-clamp depression of all measured parameters. Intracoronary Ringer's lactate, although often used as an adjunct to ischemic arrest, was not of significant value. In contrast, hearts arrested with tetrodotoxin, potassium chloride or potassium citrate showed no significant post-ischemic functional or histologic deficit. Perfusion with hypothermic Krebs-Henseleit buffer protected the myocardium better than did Ringer's lactate but less well than the tetrodotoxin or isotonic high potassium solutions. The induction of hypothermic metabolic arrest of the heart by briefly perfusing the coronary arteries via the aortic root with isotonic buffered solutions results in markedly improved myocardial tolerance to one hour of ischemia and avoids the problems of low cardiac output and ventricular irritability previously reported with hypertonic potassium citrate arrest.

Topics: Animals; Cardiac Output; Cardiopulmonary Bypass; Citrates; Coronary Circulation; Coronary Disease; Coronary Vessels; Heart Arrest; Heart Rate; Hypertonic Solutions; Isotonic Solutions; Myocardial Contraction; Perfusion; Potassium; Potassium Chloride; Rats; Tetrodotoxin

Topics: Acetylcholine; Alprenolol; Animals; Atropine; Calcium; Dogs; Electrocardiography; Electrodes; Glucagon; Heart Arrest; Heart Rate; Manganese; Norepinephrine; Ouabain; Perfusion; Propranolol; Reserpine; Sinoatrial Node; Stimulation, Chemical; Tetrodotoxin; Tyramine

Topics: Action Potentials; Animals; Arrhythmias, Cardiac; Caffeine; Calcium; Coronary Disease; Cyclic AMP; Epinephrine; Heart Arrest; Heart Conduction System; Humans; Isoproterenol; Lanthanum; Manganese; Myocardial Infarction; Potassium; Propranolol; Tetrodotoxin