Repolarization Level Research Articles

Artificial Intelligence Applied to Electrical and Non-Invasive Hemodynamic Markers in Elderly Decompensated Chronic Heart Failure Patients.

The first aim of this study was to assess the predictive power of Tend interval (Te) and non-invasive hemodynamic markers, based on bioimpedance in decompensated chronic heart failure (CHF). The second one was to verify the possible differences in repolarization and hemodynamic data between CHF patients grouped by level of left ventricular ejection fraction (LVEF). Finally, we wanted to check if repolarization and hemodynamic data changed with clinical improvement or worsening in CHF patients. Two hundred and forty-three decompensated CHF patients were studied by 5 min ECG recordings to determine the mean and standard deviation (TeSD) of Te (first study). In a subgroup of 129 patients (second study), non-invasive hemodynamic and repolarization data were recorded for further evaluation. Total in-hospital and cardiovascular mortality rates were respectively 19 and 9%. Te was higher in the deceased than in surviving subjects (Te: 120 ± 28 vs. 100 ± 25 ms) and multivariable logistic regression analysis reported that Te was related to an increase of total (χ2: 35.45, odds ratio: 1.03, 95% confidence limit: 1.02-1.05, p < 0.001) and cardiovascular mortality (χ2: 32.58, odds ratio: 1.04, 95% confidence limit: 1.02-1.06, p < 0.001). Subjects with heart failure with reduced ejection fraction (HFrEF) reported higher levels of repolarization and lower non-invasive systolic hemodynamic data in comparison to those with preserved ejection fraction (HFpEF). In the subgroup, patients with the NT-proBNP reduction after therapy showed a lower rate of Te, heart rate, blood pressures, contractility index, and left ventricular ejection time in comparison with the patients without NT-proBNP reduction. Electrical signals from ECG and bioimpedance were capable of monitoring the patients with advanced decompensated CHF. These simple, inexpensive, non-invasive, easily repeatable, and transmissible markers could represent a tool to remotely monitor and to intercept the possible worsening of these patients early by machine learning and artificial intelligence tools.

Prediction of anesthetic torsadogenicity using a human ventricular cell model.

This simulation study was designed to predict the torsadogenicity of sevoflurane and propofol in healthy control, as well as type 1 and type 2 long QT syndrome (LQT1 and LQT2, respectively), using the O'Hara-Rudy dynamic model. LQT1 and LQT2 models were simulated by decreasing the conductances of slowly and rapidly activating delayed rectifier K+ currents (IKs and IKr, respectively) by 50%, respectively. Action potential duration at 50% repolarization level (APD50) and diastolic intracellular Ca2+ concentration were measured in epicardial cell during administration of sevoflurane (1 ~ 5%) and propofol (1 ~ 10μM). Torsadogenicity can be predicted from the relationship between APD50 and diastolic intracellular Ca2+ concentration, which is classified by the decision boundary. Whereas the relationships in control and LQT1 models were distributed on nontorsadogenic side in the presence of sevoflurane at all tested concentrations, those in LQT2 models were shifted to torsadogenic side by concentrations of ≥ 2%. In all three models, propofol shifted the relationships in a direction away from the decision boundary on nontorsadogenic side. Our findings suggest that sevoflurane, but not propofol, exerts torsadogenicity in patients with reduced IKr, such as LQT2 patients. Caution should be paid to the occurrence of arrhythmia during sevoflurane anesthesia in patients with reduced IKr.

Anoxic spreading depolarization in the neonatal rat cortex in vitro.

Anoxic spreading depolarization (aSD) is a hallmark of ischemic injury in the cerebral cortex. In adults, aSD is associated with rapid and nearly complete neuronal depolarization and loss of neuronal functions. While ischemia also evokes aSD in the immature cortex, developmental aspects of neuronal behavior during aSD remain largely unknown. Here, using oxygen-glucose deprivation (OGD) ischemia model in slices of the postnatal rat somatosensory cortex, we found that immature neurons displayed much more complex behaviors: they initially moderately depolarized during aSD, then transiently repolarised (for up to tens of minutes), and only then passed to terminal depolarization. The ability to fire action potentials was maintained in neurons mildly depolarized during aSD without reaching the level of depolarization block, and these functions were regained in the majority of immature neurons during post-aSD transient repolarization. The amplitude of depolarization and the probability of depolarization block during aSD increased, whereas transient post-SD repolarization levels and duration, and associated recovery in neuronal firing decreased with age. By the end of the first postnatal month, aSD acquired an adult-like phenotype, where depolarization during aSD merged with terminal depolarization and the phase of transient recovery was lost. Thus, changes in neuronal function during aSD undergo remarkable developmental changes that may contribute to lower susceptibility of the immature neurons to ischemia.

A Mathematical Model for Electrical Activity in Pig Atrial Tissue.

State of the art mathematical models are currently used to bridge the gap between basic research conducted in the laboratory and preclinical research conducted on large animals, which ultimately paves the way for clinical translation. In this regard, there is a great need for models that can be used alongside experiments for in-depth investigation and validation. One such experimental model is the porcine atrium, which is commonly used to study the mechanisms of onset and control of atrial fibrillation in the context of its surgical management. However, a mathematical model of pig atria is lacking. In this paper, we present the first ionically detailed mathematical model of porcine atrial electrophysiology, at body temperature. The model includes 12 ionic currents, 4 of which were designed based on experimental patch-clamp data directly obtained from literature. The formulations for the other currents are adopted from the human atrial model, and modified for porcine specificity based on our measured restitution data for different action potential characteristics: resting membrane potential, action potential amplitude, maximum upstroke velocity and action potential duration and different levels of membrane voltage repolarization. The intracellular Ca2+ dynamics follows the Luo-Rudy formulation for guinea pig ventricular cardiomyocytes. The resulting model represents “normal” cells which are formulated as a system of ordinary differential equations. We extend our model to two dimensions to obtain plane wave propagation in tissue with a velocity of 0.58 m/s and a wavelength of 8 cm. The wavelength reduces to 5 cm when the tissue is paced at 200 ms. Using S1-S2 cross-field protocol, we demonstrate in an 11.26 cm square simulation domain, the ability to initiate single spiral waves (rotation period ≃ 180 ms) that remain stable for more than 40 s. The spiral tip exhibits hypermeander. In agreement with previous experimental results using pig atria, our model shows that early repolarization is primarily driven by a calcium-mediated chloride current, IClCa, which is completely inactivated at high pacing frequencies. This is a condition that occurs only in porcine atria. Furthermore, the model shows spatiotemporal chaos with reduced repolarization.

Magnetic nanocluster-mediated photothermal effect and macrophage modulation for synergistic photothermal immunotherapy of cancer.

In the tumor microenvironment, macrophages predominately exhibit M2-type functionalities which promote malignant progression and cancer metastasis, thus posing a big hurdle for current anticancer strategies. Different approaches have been exploited to reverse the macrophages towards the M1 pro-inflammatory phenotype; however, it is hard to achieve tumor regression with this macrophage modulation alone. Herein we synthesized photothermal magnetic nanoclusters (MNCs) to test their capability for reprograming M2 macrophages towards the M1 phenotype. We demonstrated that these photothermal MNCs themselves can effectively trigger this desired macrophage repolarization, increase the phagocytosis of macrophages at the tumor site, and cause subsequent T cell activation with enhanced systemic cytokine release, leading to cancer cell killing both in vitro and in vivo. More interestingly, it was found that the photothermal effect can further facilitate this immune activation to a greater extent, inducing much higher level of macrophage repolarization and T cell infiltration into the tumor site as well as eliciting a much more efficient antitumor effect compared with MNCs alone. Our findings demonstrate that MNCs combined with their photothermal effect can reverse the local suppressive environment of the tumor by macrophage and T cell modulation, providing an effective approach to trigger systemic immune responses that contribute to an enhanced overall anticancer outcome and the suppression of cancer metastasis.

Novel methods for high-resolution assessment of cardiac action potential repolarization

The profile of the action potential (AP) of cardiomyocytes contributes to the modality of ventricular repolarization of the heart. Experimentally, the examination of the AP in isolated cardiomyocytes provides information on their electrical properties, adaptations to physiological and pathological conditions, and putative ionic mechanisms involved in the process. Currently, there are no available platforms for automated assessment of AP properties and standard methodologies restrict the examination of the AP repolarization to discrete, user-defined ranges, neglecting significant intervals of the electrical recovery. This study proposes two automatic methods to assess AP profile throughout the entire repolarization phase. One method is based on AP data inversion and direct extraction of patterns describing beat-to-beat dynamics. The second method is based on evolutive singular value decomposition (ESVD), which identifies common patterns in a series of consecutive APs. The two methodologies were employed to analyze electrical signals collected from cardiomyocytes obtained from healthy mice and animals with diabetes, a condition associated with alterations of AP properties in cardiac cells. Our methodologies revealed that the duration of the early repolarization phase of the AP tended to become progressively longer during a stimulation train, whereas the late repolarization progressively shortened. Although this behavior was comparable in the two groups of cells, alterations in AP dynamics occurred at distinct repolarization levels, a feature highlighted by the ESVD approach. In conclusion, the proposed methodologies allow detailed, automatic analysis of the AP repolarization and identification of critical alterations occurring in the electrical behavior of myocytes under pathological conditions.

Влияние блокады пейсмекерных токов на сердце крыс при формировании адренергической иннервации

Hyperpolarization-activated currents (If) contribute to the generation of spontaneous electrical activity in the heart. If are modulated by the cAMP level, sympathetic, and parasympathetic parts of the autonomic nervous system. The innervation development is an important factor in the formation of the ionic current orchestra in the cardiomyocytes. The age of 6 weeks in rats poses a particular interest, because at that point the heart rate is at its slowest, and the adrenergic innervation completes its development. The aim of thist study was to investigate the role of If current in the myocardial function regulation at one of the stages of sympathetic heart innervation development. The analysis of the results revealed that in the experiments on Langendorf-isolated heart the application of If blocker ZD 7288 in 10-9-10-5 M concentrations to rats of this age led to a decrease in the heart rate. ZD 7288 in 10-8-10-5 M concentrations reduced the left ventricular pressure and the coronary flow of the isolated heart in 6-week old rats. The perfusion of the isolated heart with If blocker in 10-9 M concentration increased the left ventricular pressure, but did not affect the coronary flow. In the studies of the atrial cardiomyocyte electrical activity, ZD7288 (10-7-10-5M) increased the action potential duration at the 50% and 90% repolarization level, and reduced the action potential generation frequency. Together, these results show that the If blockade affects the heart rate, heart contraction force, and coronary flow of the isolated heart of 6-week old rats. Apparently, the heart at the stage of completion of the adrenergic innervation development has a higher density of these currents than in adult rats, which manifests in a more pronounced response to the If blockade. The changes in the heart contraction force can be attributed to the changes in the repolarization phase duration of the working cardiomyocytes.

Measurement variability of right atrial and ventricular monophasic action potential and refractory period measurements in the standing non-sedated horse

BackgroundIn human and veterinary medicine, monophasic action potential (MAP) analysis and determination of local refractory periods by contact electrode technique gives valuable information about local cardiac electrophysiological properties. It is used to investigate dysrhythmias and the impact of drugs on the myocardium. Precise measurement of total MAP duration is difficult, therefore the MAP duration is usually determined at a repolarization level of 90% (APD90). Until now, no studies are published about the feasibility of this technique in the standing non-sedated horse. In 6 healthy Warmblood horses, on two different days, an 8F quadripolar contact catheter was passed through a jugular introducer sheath and placed under ultrasound guidance at the level of the intervenous tubercle or right atrial free wall (RA), and in the right ventricular apex (RV) to record the MAP. The MAP amplitude and APD90 were measured at a resting sinus rhythm (heart rate of 30-42 bpm) and at pacing cycle lengths (PCL) of 1000 and 600 ms. The effective refractory period (ERP) was determined at PCL of 1000 and 600 ms.ResultsThe overall mean (±SD) APD90 (rest), APD90 (1000) and APD90 (600) were 263 ± 39 ms, 262 ± 41 ms, 236 ± 47 ms for the RA and 467 ± 23 ms, 412 ± 38 ms, 322 ± 29 ms for the RV. The mean ERP1000 and ERP600 were 273 ± 24 ms and 256 ± 22 ms for the RA and 386 ± 40 ms and 293 ± 30 ms for the RV. The measurement variability for the amplitude, APD90 and ERP measurements in the RA ranged between 36 and 44, 9–22 and 7–8%, respectively. The measurement variability for the amplitude, APD90 and ERP measurements in the RV ranged between 49 and 66, 6–7 and 10–12%, respectively.ConclusionsRA and RV MAP duration and ERP can be obtained by a contact electrode in standing non-sedated horses. The measurement variability varies with catheter location.

A New Class III Antiarrhythmic Drug Niferidil Prolongs Action Potentials in Guinea Pig Atrial Myocardium via Inhibition of Rapid Delayed Rectifier.

A new class III antiarrhythmic drug niferidil (RG-2) has been introduced as a highly effective therapy for cases of persistent atrial fibrillation, but ionic mechanisms of its action are poorly understood. In the present study, the effects of niferidil on action potential (AP) waveform and potassium currents responsible for AP repolarization were investigated in guinea pig atrial myocardium. APs were recorded with sharp glass microelectrodes in multicellular atrial preparations. Whole-cell patch-clamp technique was used to measure K+ currents in isolated myocytes. In multicellular atrial preparations, 10-8M niferidil effectively prolonged APs by 15.2±2.8% at 90% repolarization level. However, even the highest tested concentrations, 10-6M and 10-5M failed to prolong APs more than 32.5% of control duration. The estimated concentration of niferedil for half-maximal AP prolongation was 1.13×10-8M. Among the potassium currents responsible for AP repolarization phase, I K1 was found to be almost insensitive to niferidil. However, another inward rectifier, I KACh, was effectively suppressed by micromolar concentrations of niferidil with IC50=9.2×10-6M. I KATP was much less sensitive to the drug with IC50=2.26×10-4M. The slow component of delayed rectifier, I Ks, also demonstrated low sensitivity to niferidil-the highest used concentration, 10-4M, decreased peak I Ks density to 46.2±5.5% of control. Unlike I Ks, the rapid component of delayed rectifier, I Kr, appeared to be extremely sensitive to niferidil. The IC50 was 1.26×10-9M. I Kr measured in ventricular myocytes was found to be less sensitive to niferidil with IC50=3.82×10-8M. Niferidil prolongs APs in guinea pig atrial myocardium via inhibition of I Kr.

Electrophysiologic Studies on the Risks and Potential Mechanism Underlying the Proarrhythmic Nature of Azithromycin.

The mechanisms underlying arrhythmia induced by the clinical use of azithromycin are poorly understood. We aimed to investigate the proarrhythmic effects of azithromycin using electrocardiogram (ECG) and ion channel models. In vivo and in vitro guinea pig ECG and current and voltage clamp recordings were carried out. Azithromycin at 114.6mg/kg (three times the clinically relevant dose) reduced heart rate (HR) and prolonged the PR, QRS and rate-corrected QT (QTc) intervals of guinea pig ECG in vivo. In vitro technique revealed that azithromycin at 207.5 and 415mg/L [five and ten times clinically relevant concentration (CRC)] reduced HR and prolonged the PR, QRS and QTc intervals in the isolated guinea pig heart ECG. Both arrhythmias presented bradyarrhythmic features, mainly with reduced HR and prolonged PR interval. Action potential analysis from the guinea pig cardiomyocytes indicated that azithromycin at 830mg/L (20 times CRC) significantly prolonged the action potential durations at 50% (APD50) and 90% (APD90) of full repolarization levels with a rectangular pattern. Azithromycin significantly suppressed the L-type Ca2+ and Na+ currents from the left ventricular myocytes of guinea pig at 50% inhibiting concentrations (IC50) of 942.5±68.4mg/L (22.7 times CRC) and 1123.0±87.7mg/L (27.1 times CRC), respectively. However, azithromycin at 50 times CRC (2075mg/L) inhibited IKr current at an inhibition rate of 30.99±5.23% with an undetectable IC50. Azithromycin caused bradyarrhythmia primarily by inhibiting L-type Ca2+ and Na+ currents.

Intravenous anti-influenza drug oseltamivir will not induce torsade de pointes: Evidences from proarrhythmia model and action-potential assay

We evaluated proarrhythmic risk of intravenous oseltamivir with chronic atrioventricular block canine model (n = 4) and action-potential assay on guinea-pig right ventricle (n = 5). Oseltamivir in doses of 3–30 mg/kg, i.v. did not induce torsade de pointes in the canine model, whereas that in concentrations of 30–300 μM decreased maximum rate of phase 0 depolarization, shortened action potential duration at 30%, 60% and 90% repolarization levels, but prolonged difference in action-potential duration between 30% and 90% repolarization levels in a concentration-related manner. These results indicate that oseltamivir will not induce torsade de pointes clinically, since it inhibits both inward and outward currents.

Calcium-activated chloride current determines action potential morphology during calcium alternans in atrial myocytes.

Cardiac alternans--periodic beat-to-beat alternations in contraction, action potential (AP) morphology or cytosolic calcium transient (CaT) amplitude--is a high risk indicator for cardiac arrhythmias and sudden cardiac death. However, it remains an unresolved issue whether beat-to-beat alternations in intracellular Ca(2+) ([Ca(2+)]i ) or AP morphology are the primary cause of pro-arrhythmic alternans. Here we show that in atria AP alternans occurs secondary to CaT alternans. CaT alternans leads to complex beat-to-beat changes in Ca(2+)-regulated ion currents that determine alternans of AP morphology. We report the novel finding that alternans of AP morphology is largely sustained by the activity of Ca(2+)-activated Cl(-) channels (CaCCs). Suppression of the CaCCs significantly reduces AP alternans, while CaT alternans remains unaffected. The demonstration of a major role of CaCCs in the development of AP alternans opens new possibilities for atrial alternans and arrhythmia prevention. Cardiac alternans, described as periodic beat-to-beat alternations in contraction, action potential (AP) morphology or cytosolic Ca transient (CaT) amplitude, is a high risk indicator for cardiac arrhythmias and sudden cardiac death. We investigated mechanisms of cardiac alternans in single rabbit atrial myocytes. CaTs were monitored simultaneously with membrane currents or APs recorded with the patch clamp technique. Beat-to-beat alternations of AP morphology and CaT amplitude revealed a strong quantitative correlation. Application of voltage clamp protocols in the form of pre-recorded APs (AP-clamp) during pacing-induced CaT alternans revealed a Ca(2+)-dependent current consisting of a large outward component (4.78 ± 0.58 pA pF(-1) in amplitude) coinciding with AP phases 1 and 2 that was followed by an inward current (-0.42 ± 0.03 pA pF(-1); n = 21) during AP repolarization. Approximately 90% of the initial outward current was blocked by substitution of Cl(-) ions or application of the Cl(-) channel blocker DIDS identifying it as a Ca(2+)-activated Cl(-) current (ICaCC). The prominent AP prolongation at action potential duration at 30% repolarization level during the small alternans CaT was due to reduced ICaCC. Inhibition of Cl(-) currents abolished AP alternans, but failed to affect CaT alternans, indicating that disturbances in Ca(2+) signalling were the primary event leading to alternans, and ICaCC played a decisive role in shaping the beat-to-beat alternations in AP morphology observed during alternans.

Effects of seasonal acclimatization on temperature dependence of cardiac excitability in the roach, Rutilus rutilus.

Temperature sensitivity of electrical excitability is a potential limiting factor for performance level and thermal tolerance of excitable tissues in ectothermic animals. To test whether the rate and rhythm of the heart acclimatize to seasonal temperature changes, thermal sensitivity of cardiac excitation in a eurythermal teleost, the roach (Rutilus rutilus), was examined. Excitability of the heart was determined from in vivo electrocardiograms and in vitro microelectrode recordings of action potentials (APs) from winter and summer roach acclimatized to 4 and 18°C, respectively. Under heat ramps (3°Ch(-1)), starting from the acclimatization temperatures of the fish, heart rate increased to maximum values of 78±5 beatsmin(-1) (at 19.8±0.5°C) and 150±7beatsmin(-1) (at 28.1±0.5°C) for winter and summer roach, respectively, and then declined in both groups. Below 20°C, heart rate was significantly higher in winter than in summer roach (P<0.05), indicating positive thermal compensation. Cardiac arrhythmias appeared with rising temperature as missing QRS complexes, increase in variability of heart rate, episodes of atrial tachycardia, ventricular bradycardia and complete cessation of the heartbeat (asystole) in both winter and summer roach. Unlike winter roach, atrial APs of summer roach had a distinct early repolarization phase, which appeared as shorter durations of atrial AP at 10% and 20% repolarization levels in comparison to winter roach (P<0.05). In contrast, seasonal acclimatization had only subtle effects on ventricular AP characteristics. Plasticity of cardiac excitation appears to be necessary for seasonal improvements in performance level and thermal resilience of the roach heart.

Abstract 14317: Kvβ2 Mediates Cardiac Repolarization and Injury: Role of Pyridine Nucleotides

Background: Voltage-gated potassium channel (Kv) β2 subunits (Kvβ2) belong to the aldoketo-reductase superfamily and associate with the Kv channel modulating its function. Also, Kvβ2 binds pyridine nucleotides (NAD[P] + /NAD[P]H) with high affinity altering Kv channel gating. However, the physiological relevance of Kvβ2 in cardiac health and disease is unknown. Hypothesis: We tested the hypothesis that Kvβ2 is essential to both basal and pyridine nucleotide mediated regulation of cardiac repolarization. Methods and Results: Kvβ2 knockout (KO) and wild type (Wt) mice were utilized for this study. ECG analysis showed prolonged QTc interval (74.7± 3.7 vs. 65.6 ± 3, n=3 , p&lt;0.05 ) in KO mice when compared to Wt. Monophasic action potential (MAP) data also showed prolonged duration (ms) at 50% repolarization level in KO mouse hearts vs. Wt (MAPD50; 13.2 ± 0.3 vs. 9.7 ± 0.6, n=5-6 , p&lt;0.05 ). To test the obligatory role of Kvβ2 in pyridine nucleotide modulation of cardiac repolarization, we exposed ex vivo perfused hearts or isolated cardiomyocytes to higher lactate levels. These data revealed that acute lactate exposure leads to significant but similar raise in NADH concentration [NADH] i in both KO and Wt heart tissue. However, marked repolarization deficits appeared only in Wt group when tested utilizing ex vivo perfused hearts (MAPD50 - Wt:11.5 ± 0.7 vs. 8.3 ± 0.5, p&lt;0.05 ; KO:12.6 ± 0.7 vs. 12± 0.5, p=0.5 , ms) or isolated myocytes (ΔAPD50 – Wt: 4.7±1.6 ms, p&lt;0.05 ; KO:1.5 ± 0.7 ms, p=0.1 ). Perfusion with high pyruvate levels returned both [NADH] i and MAPD50 to basal levels in Wt mouse hearts. Similarly, we observed that a 14 day isoproterenol treatment also leads to significant increase in cardiac [NADH] i , but only the Wt mouse hearts showed significant repolarization deficits; ex-MAPD50 (5.5 ± 1.6, p&lt; 0.01 ), when compared to no changes in KO (1.9 ± 0.9, p&lt; 0.1) . Conclusions: Our results suggest that Kvβ2 regulates cardiac repolarization. Further, the differential repolarization changes despite similar increases in cardiac [NADH] i indicates an obligatory role of Kvβ2 in the pyridine nucleotide modulation of cardiac repolarization.

Abstract 19945: Acute Alcohol Intoxication and Hemorrhagic Shock Lead to Microvascular Hyperpermeability and Cardiovascular Arrhythmias

Background: Binge drinking combined with trauma is a major cause of mortality in US. It is known that acute alcohol intoxication (AAI) causes deleterious electrical changes in the heart, including involving QTc dispersion. We also recently demonstrated that acute alcohol intoxication (AAI) increases microvascular permeability. In the current study we investigated the consequences of combined hemorrhagic shock and resuscitation (HSR) and AAI on both microvascular permeability and cardiac electrical activity. Hypothesis and Methods: We hypothesized that AAI combined with HSR causes microvascular leakage and electrical dysfunction in the heart. We used an established rat model of AAI/HSR to test the microvascular and cardiac effects. Results: We identified that combined AAI/HSR significantly (p&lt;0.0007) prolongs the QTc interval (ms) compared to control water fed, sham rats (190.8±7.1 vs. 138.4±4.4, p&lt;0.05). Ex vivo acquired left ventricular monophasic action potential (AP) data revealed increased AP duration in the AAI/HSR group at 20 (9.7±0.6 vs. 5.5±0.2; p&lt;0.0004 ), 50 (16±1.1 vs. 8.8±0.6; p&lt;0.001), and 70% (24.7±2.4 vs. 19.5±0.5; p&lt;0.03) repolarization level relative to water/sham controls. Microvascular hyperpermeability was apparent in the mesenteric microcirculation in the AAI/HSR group compared to AAI/sham, water/HSR, and water/sham controls (IOI of 1061.7±208 HSR-alcohol vs. 698.4±311 HSR-water, p&lt;0.05; vs. 209.5±42 sham-alcohol, p&lt;0.001; and vs. 62.3±9 sham-water, p&lt;0.001). Conclusions: We report for the first time the cardiovascular hallmarks of AAI/HSR associated injury, which include prolonged QTc and AP durations and elevated microvascular permeability.

Effects of 4-aminopyridine on action potentials generation in mouse sinoauricular node strips.

The physiological role of Ito has yet to be clarified. The goal of this study is to investigate the possible contribution of the transient outward current (Ito) on the generation of transmembrane action potentials (APs) and the sensitivity of mouse sinoauricular node (SAN) cells to a 4-aminopyridine (4AP) as Ito blocker. The electrophysiological identification of cells was performed in the sinoauricular node artery area (nstrips = 38) of the subendocardial surface using microelectrode technique. In this study, for the first time, it was observed that dependence duration of action potential at the level of 20% repolarization (APD20) level under a 4AP concentration in the pacemaker SAN and auricular cells corresponds to a curve predicted by Hill’s equation. APD20 raised by 70% and spike duration of AP increased by 15–25%, when 4AP concentration was increased from 0.1 to 5.0 mmol/L. Auricular cells were found to be more sensitive to 4AP than true pacemaker cells. This was accompanied by a decrease in the upstroke velocity as compared to the control. Our data and previous findings in the literature lead us to hypothesize that the 4AP-sensitive current participates in the repolarization formation of pacemaker and auricular type cells. Thus, study concerning the inhibitory effects of lidocaine and TTX on APD20 can explain the phenomenon of the decrease in upstroke velocity, which, for the first time, was observed after exposure to 4AP. Duration of AP at the level of 20% repolarization (APD20) under a 4-AP concentration 0.5 mmol/L in the true pacemaker cells lengthen by 60–70% with a control.

Changes in electrical activity of working myocardium under condition of if current inhibition.

The study examined the effect of ZD7288, a blocker of hyperpolarization-activated "funny" current If, on electrical activity in working atrial and ventricular myocardium in rats. In concentrations range from 3×10(-6) to 3×10(-5) M, the agent significantly increased the duration of action potentials at 50 and 90% repolarization levels in both atrial and ventricular myocardium at the fixed stimulation rate of 5 Hz. The blocker affected neither resting potential nor the upstroke velocity of action potential. In patch-clamp experiments, ZD7288 selectively inhibited If current, but produced no effect on delayed rectifier potassium currents that determine the rate of repolarization. The described effects of ZD7288 are not related to its non-specific effects on the ionic currents except If.

CT-1-CP-induced ventricular electrical remodeling in mice.

The chronic effects of carboxyl-terminal polypeptide of Cardiotrophin-1 (CT-1-CP) on ventricular electrical remodeling were investigated. CT-1-CP, which contains 16 amino acids in sequence of the C-terminal of Cardiotrophin-1, was selected and synthesized, and then administered to Kunming mice (aged 5 weeks) by intraperitoneal injection (500 ng·g⁻¹·day⁻¹) (4 groups, n=10 and female: male=1:1 in each group) for 1, 2, 3 and 4 weeks, respectively. The control group (n=10, female: male=1:1) was injected by physiological saline for 4 weeks. The epicardial monophasic action potential (MAP) was recorded by using a contact-type MAP electrode placed vertically on the left ventricular (LV) epicardium surface, and the electrocardiogram (ECG) signal in lead II was monitored synchronously. ECG intervals (RR, PR, QRS and QT) and the amplitude of MAP (Am), the maximum upstroke velocity (Vmax), as well as action potential durations (APDs) at different repolarization levels (APD30, APD50, APD70, and APD90) of MAP were determined and analyzed in detail. There were no significant differences in RR and P intervals between CT-1-CP-treated groups and control group, but the PR segment and the QRS complex were greater in the former than in the latter (F=2.681 and 5.462 respectively, P<0.05). Though QT interval and the corrected QT interval (QTc) were shorter in CT-1-CP-treated groups than in control group, the QT dispersion (QTd) of them was greater in the latter than in the former (F=3.090, P<0.05) and increased with the time. The ECG monitoring synchronously with the MAP showed that the compression of MAP electrode on the left ventricular epicardium induced performance similar to myocardium ischemia. As compared with those before chest-opening, the PR segment and QT intervals remained basically unchanged in control group, but prolonged significantly in all CT-1-CP-treated groups and the prolongation of QT intervals increased gradually along with the time of exposure to CT-1-CP. The QRS complex had no significant change in control group, one-week and three-week CT-1-CP-treated groups, but prolonged significantly in two-week and four-week CT-1-CP-treated groups. Interestingly, the QTd after chest-opening was significantly greater than that before chest-opening in control group (t=5.242, P<0.01), but decreased along with the time in CT-1-CP-treated groups. The mean MAP amplitude, Vmax and APD were greater in CT-1-CP-treated groups than those in control group, and became more obvious along with the time. The APD in four CT-1-CP-treat groups was prolonged mainly in middle to final repolarization phase. The difference among these groups became significant in middle phase (APD50) (F=6.076, P<0.01) and increased furthermore in late and final phases (APD70: F=10.054; APD90: F=18.691, P<0.01) along with the time of injection of CT-1-CP. The chronic action of CT-1-CP might induce the adapting alteration in cardiac conductivity and ventricular repolarization. The amplitude and the Vmax of the anterior LV epicardial MAP increased obviously, and the APD prolonged mainly in late and final phase of repolarization.

Optical mapping of the electrical activity of isolated adult zebrafish hearts: acute effects of temperature

The zebrafish (Danio rerio) has emerged as an important model for developmental cardiovascular (CV) biology; however, little is known about the cardiac function of the adult zebrafish enabling it to be used as a model of teleost CV biology. Here, we describe electrophysiological parameters, such as heart rate (HR), action potential duration (APD), and atrioventricular (AV) delay, in the zebrafish heart over a range of physiological temperatures (18-28°C). Hearts were isolated and incubated in a potentiometric dye, RH-237, enabling electrical activity assessment in several distinct regions of the heart simultaneously. Integration of a rapid thermoelectric cooling system facilitated the investigation of acute changes in temperature on critical electrophysiological parameters in the zebrafish heart. While intrinsic HR varied considerably between fish, the ex vivo preparation exhibited impressively stable HRs and sinus rhythm for more than 5 h, with a mean HR of 158 ± 9 bpm (means ± SE; n = 20) at 28°C. Atrial and ventricular APDs at 50% repolarization (APD50) were 33 ± 1 ms and 98 ± 2 ms, respectively. Excitation originated in the atrium, and there was an AV delay of 61 ± 3 ms prior to activation of the ventricle at 28°C. APD and AV delay varied between hearts beating at unique HRs; however, APD and AV delay did not appear to be statistically dependent on intrinsic basal HR, likely due to the innate beat-to-beat variability within each heart. As hearts were cooled to 18°C (by 1°C increments), HR decreased by ~40%, and atrial and ventricular APD50 increased by a factor of ~3 and 2, respectively. The increase in APD with cooling was disproportionate at different levels of repolarization, indicating unique temperature sensitivities for ion currents at different phases of the action potential. The effect of temperature was more apparent at lower levels of repolarization and, as a whole, the atrial APD was the cardiac parameter most affected by acute temperature change. In conclusion, this study describes a preparation enabling the in-depth analysis of transmembrane potential dynamics in whole zebrafish hearts. Because the zebrafish offers some critical advantages over the murine model for cardiac electrophysiology, optical mapping studies utilizing zebrafish offer insightful information into the understanding and treatment of human cardiac arrhythmias, as well as serving as a model for other teleosts.

Contribution of Ca-Regulated Ion Currents to the Action Potential Morphology During Cardiac Alternans

Cardiac alternans, described as periodic beat-to-beat alternations in contraction, action potential (AP) morphology or cytosolic Ca transient (CaT) amplitude, is recognized as high risk indicator for cardiac arrhythmias, stroke and sudden cardiac death.We investigated mechanisms of cardiac alternans in single rabbit atrial myocytes. CaTs were monitored simultaneously with membrane currents or APs recorded with the patch clamp technique, and revealed a strong correlation between CaT amplitude and AP duration (APD) during alternans. Investigation of [Ca]i-Vm interactions indicates that disturbances in Ca signaling are the primary events mediating activity of Ca-regulated ion channels and leading to the changes in AP morphology. Voltage-clamp in form of pre-recorded APs (AP clamp) was used to assess the contribution of Ca-regulated membrane currents by measuring the difference between currents recorded during large and small alternans CaTs. Ca-dependent currents exhibited a large outward component (2.9 ± 1.1 pA/pF in amplitude) during AP phases 1 and 2 that was followed by an inward current (0.5 ± 0.1 pA/pF in amplitude; n=7) during AP repolarization. We also investigated contributions of Na/Ca exchange (NCX), L-type Ca, Ca-activated Cl and small conductance Ca-activated K currents to the AP morphology during Ca alternans. ∼90 % of the initial outward current was blocked by substitution of Cl ions or application of Cl channel blocker (DIDS) indicating that this current is mainly carried by Ca-activated Cl channels. In summary, during Ca alternans the prominent prolongation of AP at APD10 to APD30 repolarization levels during the small CaT is due to reduced Ca-activated Cl current while the overall effect of other Ca-sensitive currents (NCX, L-type Ca, small conductance K) cause slight shortening of AP in the APD50 to APD90 range.