Underlying mechanism of atrial fibrillation-associated Nppa-I137T mutation and cardiac effect of potential drug therapy.

BACKGROUND: More than a hundred genetic loci have been associated with atrial fibrillation (AF). But the exact mechanism remains unclear and the treatment needs to be improved. OBJECTIVE: This study aimed to investigate the mechanism and potential treatment of NPPA mutation-associated AF. METHODS: Nppa knock-in (KI, p.I137T) rats were generated, and cardiac function was evaluated. Blood pressure was recorded using a tail-cuff system. The expression levels were measured using real-time polymerase chain reaction, enzyme-linked immunosorbent assay or Western blot analysis, and RNA-sequence analysis. Programmed electrical stimulation, patch clamp, and multielectrode array were used to record the electrophysical characteristics. RESULTS: Mutant rats displayed downregulated expression of atrial natriuretic peptide but elevated blood pressure and enlarged left atrial end-diastolic diameter. Further, gene topology analysis suggested that the majority of differently expressed genes in Nppa KI rats were related to inflammation, electrical remodeling, and structural remodeling. The expression levels of C-C chemokine ligand 5 and galectin-3 involved in remodeling were higher, while there were declined levels of Nav1.5, Cav1.2, and connexin 40. AF was more easily induced in KI rats. Electrical remodeling included abbreviated action potentials, effective refractory period, increased late sodium current, and reduced calcium current, giving rise to conduction abnormalities. These electrophysiological changes could be reversed by the late sodium current blocker ranolazine and the Nav1.8 blocker A-803467. CONCLUSION: Our findings suggest that structural remodeling related to inflammation and fibrosis and electrical remodeling involved in late sodium current underly the major effects of the Nppa (p.I137T) variant to induce AF, which can be attenuated by the late sodium current blocker and Nav1.8 blocker.

Bupleurum exerts antiarrhythmic effects by inhibiting L-type calcium channels in mouse ventricular myocytes.

BACKGROUND: Bupleurum (Bup), is a traditional effective medicine to treat colds and fevers in clinics. Multiple studies have demonstrated that Bup exhibites various biological activities, including cardioprotective effects, anti-inflammatory, anticancer, antipyretic, antimicrobial, and antiviral effects, etc. Currently, the effects of Bup on cardiac electrophysiology have not been reported yet. METHODS: Electrocardiogram recordings were used to investigate the effects of Bup on aconitine-induced arrhythmias. Patch-clamp techniques were used to explore the effects of Bup on APs and ion currents. RESULTS: Bup reduced the incidence of ventricular fibrillation (VF) and delayed the onset time of ventricular tachycardia (VT) in mice. Additionally, Bup (40 mg/mL) suppressed DADs induced by high-Ca2+ and shortened action potential duration at 50 % completion of repolarization (APD50) and action potential duration at 90 % completion of repolarization (APD90) to 60.89 % ± 8.40 % and 68.94 % ± 3.24 % of the control, respectively. Moreover, Bup inhibited L-type calcium currents (ICa.L) in a dose-dependent manner, with an IC50 value of 25.36 mg/mL. Furthermore, Bup affected the gated kinetics of L-type calcium channels by slowing down steady-state activation, accelerating the steady-state inactivation, and delaying the inactivation-recovery process. However, Bup had no effects on the Transient sodium current (INa.T), ATX II-increased late sodium current (INa.L), transient outward current (Ito), delayed rectifier potassium current (IK), or inward rectifier potassium current (IK1). CONCLUSION: Bup is an antiarrhythmic agent that may exert its antiarrhythmic effects by inhibiting L-type calcium channels.

Responsiveness to Platelet Transfusions in Pediatric Patients with Thrombocytopenia: Incidence, Clinical Variables.

BACKGROUND: Refractoriness to platelet transfusion has not been adequately studied in pediatric patients with thrombocytopenia. Our objectives were: (1) to describe the practice of platelet transfusion in pediatric patients with thrombocytopenia of various etiologies; (2) to assess the responsiveness to platelet transfusions and clinical variables affecting platelet transfusions response; and (3) to evaluate incidence of PTR. METHODS: A retrospective study included pediatric patients with thrombocytopenia admitted to a tertiary children's hospital who received ≥ 1 platelet transfusion during hospitalization. Responsiveness was measured by corrected count increment (CCI), poor platelet transfusion response (PPTR), and platelet transfusion refractoriness (PTR). RESULTS: A total of 334 patients were eligible for the study and received 1,164 transfusions, with a median of 2 (IQR: 1 - 5) platelet transfusions. Patients admitted with hematologic malignancies had the highest median number of platelet transfusions (5, IQR: 4 - 10). The median CCI of 1,164 platelet post-transfusions was 17.0 (IQR: 9.4 - 24.6) and the incidence of PPTR was 11.9%. Patients admitted with ITP had the lowest median CCI (7.6, IQR: 1.0 - 12.5) and the highest incidence of PPTR (36.4%, 8/22). Older age of platelet components, low doses of platelet transfusion, increasing number of platelet transfusions (≥ 5), splenomegaly, bleeding, DIC, shock, ECMO supported, and HLA antibody-positive were independent risk factors for PPTR. Finally, the incidence of PTR was 11.4%. CONCLUSIONS: Practical experience of clinicians regarding the use of apheresis platelets in pediatric patients is determined. Highlight that PTR is not a low probability event when apheresis platelets are received in pediatric patients.

Comparison of restrictive and liberal red blood cell suspension transfusion and analysis of influencing factors on prognosis of premature infants.

OBJECTIVE: To investigate the influence of restrictive and liberal red blood cell suspension (RBCs) transfusions on the prognosis of premature infants and to analyze the influencing factors to provide a reference for the transfusion strategy of preterm infants. METHODS: Retrospective analysis was conducted on 85 cases of anemic premature infants treated in our center, including 63 cases in the restrictive transfusion group and 22 in the liberal transfusion group. RESULTS: RBCs transfusions were effective in both groups, and there were no statistically significant differences in post-transfusion hemoglobin and hematocrit between the two groups (P > 0.05). The outcome events: the duration of ventilatory support was statistically prolonger in the restrictive group compared with the liberal group (P < 0.001); however, the differences in mortality, the increased weight before discharge, and length of stay in the hospital within the two groups were not statistically significant (P = 0.237, 0.36 and 0.771, respectively). Univariate survival analysis showed that age, birth weight, Apgar 1 min and Apgar 10 min scores were the influencing factors for death, with P values of 0.035, 0.004, <0.001, and 0.013, respectively; COX regression analysis showed that Apgar 1 min score was an independent factor of the survival time of preterm infants (P = 0.002). CONCLUSION: Compared with the restrictive transfusion group, liberal transfusion patients presented a shorter duration of ventilatory support, which is more beneficial to the prognosis of premature infants.

[Serological Diagnosis and Clinical Data Analysis of Neonatal Alloimmune Thrombocytopenia].

OBJECTIVE: To investigate the pathogenesis and clinical diagnosis of fetal/neonatal alloimmune thrombocytopenia (FNAIT) and analyze the laboratory test results and clinical data related to the disease, so as to provide reference for clinical treatment and improvement of prognosis. METHODS: The clinical data of six neonatal patients with FNAIT in the Neonatology Department of our hospital from March 2017 to September 2020 were retrospectively analyzed, which included laboratory diagnosis, clinical symptoms, treatment, and prognosis. RESULTS: Among six patients, two cases occurred in the first pregnancy and four cases in the second pregnancy. The platelet count of six cases were decreased at admission or during hospitalization and maternal and neonatal serum autoimmune platelet antibody tests were positive. Five cases were accompanied by different degrees of skin and facial bleeding spots or petechiae and ecchymosis, intracranial hemorrhage. Four cases were treated with immunoglobulin and/or steroid hormone therapy (one of them received cross-matched platelets transfusion), while the symptoms of the other two cases improved spontaneously. Five cases recovered and were discharged from the hospital, while one case had not recovered but the family members requested to be discharged forwardly. Four cases were hospitalized within two weeks, but two cases were hospitalized for more than two weeks due to other diseases or factors (e.g., neonatal sepsis, neonatal enteritis, congenital heart disease, neonatal asphyxia, etc.). CONCLUSION: FNAIT is characterized by decreased platelet count, with or without bleeding symptoms, and may occur in the first and following pregnancy. FNAIT can recover spontaneously or have a good prognosis after treatment. However, the complication with other diseases or factors may affect the prognosis.

Lymph Node Dissection Is a Risk Factor for Short-Term Cough after Pulmonary Resection.

Cough is a common complication after pulmonary resection. However, the factors associated with cough that develop after pulmonary resection are still controversial. In this study, we used the Simplified Cough Score (SCS) and the Leicester Cough Questionnaire (LCQ) score to investigate potential risk factors for postoperative cough. Between January 2017 and June 2021, we collected the clinical data of 517 patients, the SCS at three days after surgery and the LCQ at two weeks and six weeks after surgery. Then, univariate and multivariate analyses were used to identify the independent risk factors for postoperative cough. The clinical baseline data of the cough group and the non-cough group were similar. However, the cough group had longer operation time and more blood loss. The patients who underwent lobectomy were more likely to develop postoperative cough than the patients who underwent segmentectomy and wedge resection, while the patients who underwent systematic lymph node dissection were more likely to develop postoperative cough than the patients who underwent lymph node sampling and those who did not undergo lymph node resection. When the same lymph node management method was applied, there was no difference in the LCQ scores between the patients who underwent wedge resection, lobectomy and segmentectomy. The lymph node resection method was an independent risk factor for postoperative cough (p < 0.001). Conclusions: Lymph node resection is an independent risk factor for short-term cough after pulmonary resection with video-assisted thoracoscopic surgery, and damage to the vagus nerve and its branches (particularly the pulmonary branches) is a possible cause of short-term cough. The mechanism of postoperative cough remains to be further studied.

Inhibition of Ca2+-dependent protein kinase C rescues high calcium-induced pro-arrhythmogenic cardiac alternans in rabbit hearts.

Cardiac alternans closely linked to calcium dysregulation is a crucial risk factor for fatal arrhythmia causing especially sudden death. Calcium overload is well-known to activate Ca2+-dependent protein kinase C (PKC); however, the effects of PKC on arrhythmogenic cardiac alternans have not yet been investigated. This study aimed to determine the contributions of PKC activities in cardiac alternans associated with calcium cycling disturbances. In the present study, action potential duration alternans (APD-ALT) induced by high free intracellular calcium ([Ca2+]i) exerted not only in a calcium concentration-dependent manner but also in a frequency-dependent manner. High [Ca2+]i-induced APD-ALT was suppressed by not only BAPTA-AM but also nifedipine. On the other hand, PKC inhibitors BIM and Gö 6976 eliminated high [Ca2+]i-induced APD-ALT, and PKC activator PMA was found to induce APD-ALT at normal [Ca2+]i condition. Furthermore, BIM effectively prevented calcium transient alternans (CaT-ALT) and even CaT disorders caused by calcium overload. Moreover, BIM not only eliminated electrocardiographic T-wave alternans (TWA) caused by calcium dysregulation, but also lowered the incidence of ventricular arrhythmias in isolated hearts. What's more, BIM prevented the expression of PKC α upregulated by calcium overload in high calcium-perfused hearts. We firstly found that pharmacologically inhibiting Ca2+-dependent PKC over-activation suppressed high [Ca2+]i-induced cardiac alternans. This recognition indicates that inhibition of PKC activities may become a therapeutic target for the prevention of pro-arrhythmogenic cardiac alternans associated with calcium dysregulation.

Eleutheroside B, a selective late sodium current inhibitor, suppresses atrial fibrillation induced by sea anemone toxin II in rabbit hearts.

Eleutheroside B (EB) is the main active constituent derived from the Chinese herb Acanthopanax senticosus (AS) that has been reported to possess cardioprotective effects. In this study we investigated the effects of EB on cardiac electrophysiology and its suppression on atrial fibrillation (AF). Whole-cell recording was conducted in isolated rabbit atrial myocytes. The intracellular calcium ([Ca2+]i) concentration was measured using calcium indicator Fura-2/AM fluorescence. Monophasic action potential (MAP) and electrocardiogram (ECG) synchronous recordings were conducted in Langendorff-perfused rabbit hearts using ECG signal sampling and analysis system. We showed that EB dose-dependently inhibited late sodium current (INaL), transient sodium current (INaT), and sea anemone toxin II (ATX II)-increased INaL with IC50 values of 167, 1582, and 181 µM, respectively. On the other hand, EB (800 µM) did not affect L-type calcium current (ICaL), inward rectifier potassium channel current (IK), and action potential duration (APD). Furthermore, EB (300 µM) markedly decreased ATX II-prolonged the APD at 90% repolarization (APD90) and eliminated ATX II-induced early afterdepolarizations (EADs), delayed afterdepolarizations (DADs), and triggered activities (TAs). Moreover, EB (200 µM) significantly suppressed ATX II-induced Na+-dependent [Ca2+]i overload in atrial myocytes. In the Langendorff-perfused rabbit hearts, application of EB (200 µM) or TTX (2 µM) substantially decreased ATX II-induced incidences of atrial fibrillation (AF), ventricular fibrillation (VF), and heart death. These results suggest that augmented INaL alone is sufficient to induce AF, and EB exerts anti-AF actions mainly via blocking INaL, which put forward the basis of pharmacology for new clinical application of EB.

Isoliensinine Eliminates Afterdepolarizations Through Inhibiting Late Sodium Current and L-Type Calcium Current.

Isoliensinine (IL) extracted from lotus seed has a good therapeutic effect on cardiovascular diseases. However, its effect on ion channels of ventricular myocytes is still unclear. We used whole-cell patch-clamp techniques to detect the effects of IL on transmembrane ion currents and action potential (AP) in isolated rabbit left ventricular myocytes. IL inhibited the transient sodium current (INaT), late sodium current (INaL) enlarged by sea anemone toxin (ATX II) and L-type calcium current (ICaL) in a concentration-dependent manner without affecting inward rectifier potassium current (IK1) and delayed rectifier potassium current (IK). These inhibitory effects are mainly manifested as reduced the AP amplitude (APA) and maximum depolarization velocity (Vmax) and shortened the action potential duration (APD), but had no significant effect on the resting membrane potential (RMP). Moreover, IL significantly eliminated ATX II-induced early afterdepolarizations (EADs) and high extracellular calcium-induced delayed afterdepolarizations (DADs). These results revealed that IL effectively eliminated EADs and DADs through inhibiting INaL and ICaL in ventricular myocytes, which indicates it has potential antiarrhythmic action.

Curcumin, a Multi-Ion Channel Blocker That Preferentially Blocks Late Na+ Current and Prevents I/R-Induced Arrhythmias.

Increasing evidence shows that Curcumin (Cur) has a protective effect against cardiovascular diseases. However, the role of Cur in the electrophysiology of cardiomyocytes is currently not entirely understood. Therefore, the present study was conducted to investigate the effects of Cur on the action potential and transmembrane ion currents in rabbit ventricular myocytes to explore its antiarrhythmic property. The whole-cell patch clamp was used to record the action potential and ion currents, while the multichannel acquisition and analysis system was used to synchronously record the electrocardiogram and monophasic action potential. The results showed that 30 µmol/L Cur shortened the 50 and 90% repolarization of action potential by 17 and 7%, respectively. In addition, Cur concentration dependently inhibited the Late-sodium current (I Na.L), Transient-sodium current (I Na.T), L-type calcium current (I Ca.L), and Rapidly delayed rectifying potassium current (I Kr), with IC50 values of 7.53, 398.88, 16.66, and 9.96 µmol/L, respectively. Importantly, the inhibitory effect of Cur on I Na.L was 52.97-fold higher than that of I Na.T. Moreover, Cur decreased ATX II-prolonged APD, suppressed the ATX II-induced early afterdepolarization (EAD) and Ca2+-induced delayed afterdepolarization (DAD) in ventricular myocytes, and reduced the occurrence and average duration of ventricular tachycardias and ventricular fibrillations induced by ischemia-reperfusion injury. In conclusion, Cur inhibited I Na.L, I Na.T, I Ca.L, and I Kr; shortened APD; significantly suppressed EAD and DAD-like arrhythmogenic activities at the cellular level; and exhibited antiarrhythmic effect at the organ level. It is first revealed that Cur is a multi-ion channel blocker that preferentially blocks I Na.L and may have potential antiarrhythmic property.

Late Sodium Current in Atrial Cardiomyocytes Contributes to the Induced and Spontaneous Atrial Fibrillation in Rabbit Hearts.

Increased late sodium current (INa) induces long QT syndrome 3 with increased risk of atrial fibrillation (AF). The role of atrial late INa in the induction of AF and in the treatment of AF was determined in this study. AF parameters were measured in isolated rabbit hearts exposed to late INa enhancer and inhibitors. Late INa from isolated atrial and ventricular myocytes were measured using whole-cell patch-clamp techniques. We found that induced-AF by programmed S1S2 stimulation and spontaneous episodes of AF were recorded in hearts exposed to either low (0.1-3 nM) or high (3-10 nM) concentrations of ATX-II (n = 10). Prolongations in atrial monophasic action potential duration at 90% completion of repolarization and effective refractory period by ATX-II (0.1-15 nM) were greater in hearts paced at slow than at fast rates (n = 5-10, P < 0.05). Both endogenous and ATX-II-enhanced late INa density were greater in atrial than that in ventricular myocytes (n = 9 and 8, P < 0.05). Eleclazine and ranolazine reduced AF window and AF burden in association with the inhibition of both endogenous and enhanced atrial late INa with half maximal inhibitory concentrations (IC50) of 1.14 and 9.78, and 0.94 and 8.31 µM, respectively. The IC50s for eleclazine and ranolazine to inhibit peak INa were 20.67 and 101.79 µM, respectively, in atrial myocytes. In conclusion, enhanced late INa in atrial myocytes increases the susceptibility for AF. Inhibition of either endogenous or enhanced late INa, with increased atrial potency of drugs is feasible for the treatment of AF.

Antiarrhythmic effect of crotonoside by regulating sodium and calcium channels in rabbit ventricular myocytes.

AIMS: Detect the antiarrhythmic effect of crotonoside (Cro). MAIN METHODS: We used whole-cell patch-clamp techniques to detect the effects of Cro on action potentials (APs) and transmembrane ion currents in isolated rabbit left ventricular myocytes. We also verified the effect of Cro on ventricular arrhythmias caused by aconitine in vivo. KEY FINDINGS: Cro reduced the maximum depolarization velocity (Vmax) of APs and shortened the action potential duration (APD) in a concentration-dependent manner, but it had no significant effect on the resting membrane potential (RMP) or action potential amplitude (APA). It also inhibited the peak sodium current (INa) and L-type calcium current (ICaL) in a concentration-dependent manner with half-maximal inhibitory concentrations (IC50) of 192 µmol/L and 159 µmol/L, respectively. However, Cro had no significant effects on the inward rectifier potassium current (IK1) or rapidly activating delayed rectifier potassium current (IKr). Sea anemone toxin II (ATX II) increased the late sodium current (INaL), but Cro abolished this effect. Moreover, Cro significantly abolished ATX II-induced early afterdepolarizations (EADs) and high extracellular Ca2+ concentration (3.6 mmol/L)-induced delayed afterdepolarizations (DADs). We also verified that Cro effectively delayed the onset time and reduced the incidence of ventricular arrhythmias caused by aconitine in vivo. SIGNIFICANCE: These results revealed that Cro effectively inhibits INa, INaL, and ICaL in ventricular myocytes. Cro has antiarrhythmic potential and thus deserves further study.

Increase in CO2 levels by upregulating late sodium current is proarrhythmic in the heart.

BACKGROUND: Increased CO2 levels in the general circulation and/or in the myocardium are common under pathologic conditions. OBJECTIVE: The purpose of this study was to test the hypothesis that an increase in CO2 levels, and not just the subsequent extra- or intracellular acidosis, would augment late sodium current (INa,L) and contribute to arrhythmogenesis in hearts with reduced repolarization reserve. METHODS: Monophasic action potential durations at 90% completion of repolarization (MAPD90) from isolated rabbit hearts, INa,L, and extra- (pHo) and intracellular pH (pHi) values from cardiomyocytes using the whole-cell patch-clamp techniques and 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF-AM), respectively, were measured. RESULTS: Increasing CO2 levels from 5% to 10% and 20% and administration of 1 nM sea anemone toxin (ATX)-II increased INa,L and prolonged both epicardial and endocardial MAPD90 (n = 7 and 10, respectively) without causing arrhythmic activities. Compared to 5% CO2, 10% and 20% CO2 decreased pHo and pHi in hearts treated with 1 nM ATX-II, caused greater prolongation of MAPD90, and elicited ventricular tachycardias. Increasing CO2 levels from 5% to 10% and 20% with pHo maintained at 7.4 produced smaller changes in pHi (P <.05) but similar increases in INa,L, prolongation of MAPD90, and incidence of ventricular tachycardias (n = 8). Inhibition of INa,L reversed the increase in INa,L, suppressed MAPD90 prolongations, and ventricular tachycardias induced by 20% CO2. Increased phospho-calmodulin-dependent protein kinase II-δ (CaMKIIδ) and phospho-NaV1.5 protein levels in hearts treated with 20% CO2 was attenuated by eleclazine. CONCLUSION: Increased CO2 levels enhance INa,L and are proarrhythmic factors in hearts with reduced repolarization reserve, possibly via mechanisms related to phosphorylation of CaMKIIδ and NaV1.5.

Ginsenoside Rb1 exerts antiarrhythmic effects by inhibiting INa and ICaL in rabbit ventricular myocytes.

Ginsenoside Rb1 exerts its pharmacological action by regulating sodium, potassium and calcium ion channels in the membranes of nerve cells. These ion channels are also present in cardiomyocytes, but no studies have been reported to date regarding the effects of Rb1 on cardiac sodium currents (INa), L-type calcium currents (ICaL) and action potentials (APs). Additionally, the antiarrhythmic potential of Rb1 has not been assessed. In this study, we used a whole-cell patch clamp technique to assess the effect of Rb1 on these ion channels. The results showed that Rb1 inhibited INa and ICaL, reduced the action potential amplitude (APA) and maximum upstroke velocity (Vmax), and shortened the action potential duration (APD) in a concentration-dependent manner but had no effect on the inward rectifier potassium current (IK1), delayed rectifier potassium current (IK) or resting membrane potential (RMP). We also designed a pathological model at the cellular and organ level to verify the role of Rb1. The results showed that Rb1 abolished high calcium-induced delayed afterdepolarizations (DADs), depressed the increase in intracellular calcium ([Ca2+]i), relieved calcium overload and protected cardiomyocytes. Rb1 can also reduce the occurrence of ventricular premature beats (VPBs) and ventricular tachycardia (VT) in ischemia-reperfusion (I-R) injury.

Sodium Houttuyfonate Inhibits Voltage-Gated Peak Sodium Current and Anemonia Sulcata Toxin II-Increased Late Sodium Current in Rabbit Ventricular Myocytes.

AIM: Sodium houttuyfonate (SH), a chemical compound originating from Houttuynia cordata, has been reported to have anti-inflammatory, antibacterial, and antifungal effects, as well as cardioprotective effects. In this study, we investigated the effects of SH on cardiac electrophysiology, because to the best of our knowledge, this issue has not been previously investigated. METHODS: We used the whole-cell patch-clamp technique to explore the effects of SH on peak sodium current (INa.P) and late sodium current (INa.L) in isolated rabbit ventricular myocytes. To test the drug safety of SH, we also investigated the effect of SH on rapidly activated delayed rectifier potassium current (IKr). RESULTS: SH (1, 10, 50, and 100 µmol/L) inhibited INa.P in a concentration-dependent manner with an IC50 of 78.89 µmol/L. In addition, SH (100 µmol/L) accelerated the steady state inactivation of INa.P. Moreover, 50 and 100 µmol/L SH inhibited Anemonia sulcata toxin II (ATX II)-increased INa.L by 30.1 and 57.1%, respectively. However, SH (50 and 100 µmol/L) only slightly affected IKr. CONCLUSIONS: The inhibitory effects of SH on ATX II-increased INa.L may underlie the electrophysiological mechanisms of the cardioprotective effects of SH; SH has the potential to be an effective and safe antiarrhythmic drug.

Barbaloin inhibits ventricular arrhythmias in rabbits by modulating voltage-gated ion channels.

Barbaloin (10-ß-D-glucopyranosyl-1,8-dihydroxy-3-(hydroxymethyl)-9(10H)-anthracenone) is extracted from the aloe plant and has been reported to have anti-inflammatory, antitumor, antibacterial, and other biological activities. Here, we investigated the effects of barbaloin on cardiac electrophysiology, which has not been reported thus far. Cardiac action potentials (APs) and ionic currents were recorded in isolated rabbit ventricular myocytes using whole-cell patch-clamp technique. Additionally, the antiarrhythmic effect of barbaloin was examined in Langendorff-perfused rabbit hearts. In current-clamp recording, application of barbaloin (100 and 200 µmol/L) dose-dependently reduced the action potential duration (APD) and the maximum depolarization velocity (Vmax), and attenuated APD reverse-rate dependence (RRD) in ventricular myocytes. Furthermore, barbaloin (100 and 200 µmol/L) effectively eliminated ATX II-induced early afterdepolarizations (EADs) and Ca2+-induced delayed afterdepolarizations (DADs) in ventricular myocytes. In voltage-clamp recording, barbaloin (10-200 µmol/L) dose-dependently inhibited L-type calcium current (ICa.L) and peak sodium current (INa.P) with IC50 values of 137.06 and 559.80 µmol/L, respectively. Application of barbaloin (100, 200 µmol/L) decreased ATX II-enhanced late sodium current (INa.L) by 36.6%±3.3% and 71.8%±6.5%, respectively. However, barbaloin up to 800 µmol/L did not affect the inward rectifier potassium current (IK1) or the rapidly activated delayed rectifier potassium current (IKr) in ventricular myocytes. In Langendorff-perfused rabbit hearts, barbaloin (200 µmol/L) significantly inhibited aconitine-induced ventricular arrhythmias. These results demonstrate that barbaloin has potential as an antiarrhythmic drug.

Andrographolide inhibits arrhythmias and is cardioprotective in rabbits.

Andrographolide has a protective effect on the cardiovascular system. To study its cardic-electrophysiological effects, action potentials and voltage-gated Na+ (INa), Ca2+ (ICaL), and K+ (IK1, IKr, Ito and IKur) currents were recorded using whole-cell patch clamp and current clamp techniques. Additionally, the effects of andrographolide on aconitine-induced arrhythmias were assessed on electrocardiograms in vivo. We found that andrographolide shortened action potential duration and reduced maximum upstroke velocity in rabbit left ventricular and left atrial myocytes. Andrographolide attenuated rate-dependence of action potential duration, and reduced or abolished delayed afterdepolarizations and triggered activities induced by isoproterenol (1 µM) and high calcium ([Ca2+]o=3.6 mM) in left ventricular myocytes. Andrographolide also concentration-dependently inhibited INa and ICaL, but had no effect on Ito, IKur, IK1, or IKr in rabbit left ventricular and left atrial myocytes. Andrographolide treatment increased the time and dosage thresholds of aconitine-induced arrhythmias, and reduced arrhythmia incidence and mortality in rabbits. Our results indicate that andrographolide inhibits cellular arrhythmias (delayed afterdepolarizations and triggered activities) and aconitine-induced arrhythmias in vivo, and these effects result from INa and ICaL inhibition. Andrographolide may be useful as a class I and IV antiarrhythmic therapeutic.

Wenxin Keli diminishes Ca2+ overload induced by hypoxia/reoxygenation in cardiomyocytes through inhibiting INaL and ICaL.

BACKGROUND: An increase in the late sodium current (INaL ) causes intracellular Na+ overload and subsequently intracellular Ca2+ ([Ca2+ ]i ) overload via the stimulated reverse Na+ -Ca2+ exchange (NCX). Wenxin Keli (WXKL) is an effective antiarrhythmic Chinese herb extract, but the underlying mechanisms are unclear. METHODS AND RESULTS: The INaL , NCX current (INCX ), L-type Ca2+ current (ICaL ), and action potentials were recorded using the whole-cell patch-clamp technique in rabbit ventricular myocytes. Myocyte [Ca2+ ]i transients were measured using a dual excitation fluorescence photomultiplier system. WXKL decreased the enhanced INaL , reverse INCX , diastolic [Ca2+ ]i , and the amplitude of Ca2+ transients induced by sea anemone toxin II (ATX II, a specific INaL channel opener) in a concentration-dependent manner. Hypoxia increased INaL , INCX , and diastolic [Ca2+ ]i , and decreased amplitude of [Ca2+ ]i transients. Hypoxia-reoxygenation aggravated these changes and induced spontaneous [Ca2+ ]i transients and hypercontraction in 86% cells (6/7). The application of WXKL during hypoxia or reoxygenation periods decreased the increased INaL , INCX , and diastolic [Ca2+ ]i , and prevented those events in 82% cells (9/11) under hypoxia-reoxygenation conditions. WXKL also inhibited the ICaL in a dose-dependent manner. Furthermore, WXKL shortened the action potential duration and completely abolished ATX II-induced early afterdepolarizations from 9/9 to /9. In isolated heart electrocardiogram recordings, WXKL inhibited ischemia-reperfusion induced ventricular premature beats and tachycardia. CONCLUSIONS: WXKL attenuated [Ca2+ ]i overload induced by hypoxia-reoxygenation in ventricular myocytes through inhibiting INaL and ICaL and prevents arrhythmias. This could, at least partly, contribute to the antiarrhythmic effects of WXKL.

Icariin, a Novel Blocker of Sodium and Calcium Channels, Eliminates Early and Delayed Afterdepolarizations, As Well As Triggered Activity, in Rabbit Cardiomyocytes.

Icariin, a flavonoid monomer from Herba Epimedii, has confirmed pharmacological and biological effects. However, its effects on arrhythmias and cardiac electrophysiology remain unclear. Here we investigate the effects of icariin on ion currents and action potentials (APs) in the rabbit myocardium. Furthermore, the effects of icariin on aconitine-induced arrhythmias were assessed in whole rabbits. Ion currents and APs were recorded in voltage-clamp and current-clamp mode in rabbit left ventricular myocytes (LVMs) and left atrial myocytes (LAMs), respectively. Icariin significantly shortened action potential durations (APDs) at 50 and 90% repolarization (APD50 and APD90) and reduced AP amplitude (APA) and the maximum upstroke velocity (Vmax) of APs in LAMs and LVMs; however, icariin had no effect on resting membrane potential (RMP) in these cells. Icariin decreased the rate-dependence of the APD and completely abolished anemonia toxin II (ATX-II)-induced early afterdepolarizations (EADs). Moreover, icariin significantly suppressed delayed afterdepolarizations (DADs) and triggered activities (TAs) elicited by isoproterenol (ISO, 1 µM) and high extracellular calcium concentrations ([Ca2+]o, 3.6 mM) in LVMs. Icariin also decreased INaT in a concentration-dependent manner in LAMs and LVMs, with IC50 values of 12.28 ± 0.29 µM (n = 8 cells/4 rabbits) and 11.83 ± 0.92 µM (n = 10 cells/6 rabbits; p > 0.05 vs. LAMs), respectively, and reversed ATX-II-induced INaL in a concentration-dependent manner in LVMs. Furthermore, icariin attenuated ICaL in a dose-dependent manner in LVMs. The corresponding IC50 value was 4.78 ± 0.89 µM (n = 8 cells/4 rabbits), indicating that the aforementioned current in LVMs was 2.8-fold more sensitive to icariin than ICaL in LAMs (13.43 ± 2.73 µM; n = 9 cells/5 rabbits). Icariin induced leftward shifts in the steady-state inactivation curves of INaT and ICaL in LAMs and LVMs but did not have a significant effect on their activation processes. Moreover, icariin had no effects on IK1 and IKr in LVMs or Ito and IKur in LAMs. These results revealed for the first time that icariin is a multichannel blocker that affects INaT, INaL and ICaL in the myocardium and that the drug had significant inhibitory effects on aconitine-induced arrhythmias in whole rabbits. Therefore, icariin has potential as a class I and IV antiarrhythmic drug.