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.

Modulation of late sodium current by Ca2+ -calmodulin-dependent protein kinase II, protein kinase C and Ca2+ during hypoxia in rabbit ventricular myocytes.

NEW FINDINGS: What is the central question of this study? Hypoxia-induced increase in late sodium current (INa,L ) is associated with conditions causing cellular Ca2+ overload and contributes to arrhythmogenesis in the ventricular myocardium. The INa,L is an important drug target. We investigated intracellular signal transduction pathways involved in modulation of INa,L during hypoxia. What is the main finding and its importance? Hypoxia caused increases in INa,L , reverse Na+ -Ca2+ exchange current and diastolic [Ca2+ ], which were attenuated by inhibitors of Ca2+ -calmodulin-dependent protein kinase II (CaMKII) and protein kinase C and by a Ca2+ chelator. The findings suggest that CaMKII, protein kinase C and Ca2+ all participate in mediation of the effect of hypoxia to increase INa,L . Hypoxia leads to augmentation of the late sodium current (INa,L ) and cellular Na+ loading, increased reverse Na+ -Ca2+ exchange current (reverse INCX ) and intracellular Ca2+ loading in rabbit ventricular myocytes. The purpose of this study was to determine the intracellular signal transduction pathways involved in the modulation of INa,L during hypoxia in ventricular myocytes. Whole-cell and cell-attached patch-clamp techniques were used to record INa,L , and the whole-cell mode was also used to record reverse INCX and to study intercellular signal transduction mechanisms that mediate the increased INa,L . Dual excitation fluorescence photomultiplier systems were used to record the calcium transient in ventricular myocytes. Hypoxia caused increases of INa,L and reverse INCX . These increases were attenuated by KN-93 (an inhibitor of Ca2+ -calmodulin-dependent protein kinase II), bisindolylmaleimide VI (BIM; an inhibitor of protein kinase C) and BAPTA AM (a Ca2+ chelator). KN-93, BIM and BAPTA AM had no effect on INa,L in normoxia. In studies of KN-93, hypoxia alone increased the density of INa,L from -0.31 ± 0.02 to -0.66 ± 0.03 pA pF-1 (n = 6, P < 0.01 versus control) and the density of reverse INCX from 1.02 ± 0.06 to 1.91 ± 0.20 pA pF-1 (n = 7, P < 0.01 versus control) in rabbit ventricular myocytes. In the presence of 1 µm KN-93, the densities of INa,L and reverse INCX during hypoxia were significantly attenuated to -0.44 ± 0.03 (n = 6, P < 0.01 versus hypoxia) and 1.36 ± 0.15 pA pF-1 (n = 7, P < 0.01 versus hypoxia), respectively. In studies of BIM, hypoxia increased INa,L from -0.30 ± 0.03 to -0.60 ± 0.03 pA pF-1 (n = 6, P < 0.01 versus control) and reverse INCX from 0.91 ± 0.10 to 1.71 ± 0.27 pA pF-1 (n = 6, P < 0.01 versus control). In the presence of 1 µm BIM, the densities of INa,L and reverse INCX during hypoxia were significantly attenuated to -0.48 ± 0.02 (n = 6, P < 0.01 versus hypoxia) and 1.33 ± 0.21 pA pF-1 (n = 6, P < 0.01 versus hypoxia), respectively. In studies of BAPTA AM, hypoxia increased INa,L from -0.26 ± 0.04 to -0.63 ± 0.05 pA pF-1 (n = 6, P < 0.01 versus control) and reverse INCX from 0.86 ± 0.09 to 1.68 ± 0.35 pA pF-1 (n = 6, P < 0.01 versus control). The effects of hypoxia on INa,L and reverse INCX were significantly attenuated in the presence of 1 mm BAPTA AM to -0.39 ± 0.02 (n = 6, P < 0.01 versus hypoxia) and 1.12 ± 0.27 pA pF-1 (n = 6, P < 0.01 versus hypoxia), respectively. Results of single-channel studies showed that hypoxia apparently increased the mean open probability and mean open time of sodium channels. These effects were inhibited by either 1 µm KN-93 or 1 mm BAPTA AM. The suppressant effects of drug interventions were reversed upon washout. In addition, KN-93, BIM and BAPTA AM also reversed the hypoxia-enhanced diastolic Ca2+ concentration and the attenuated amplitude of the [Ca2+ ]i transient, maximal velocities of Ca2+ increase and Ca2+ decay. In summary, the findings suggest that Ca2+ -calmodulin-dependent protein kinase II, protein kinase C and Ca2+ all participate in mediation of the effect of hypoxia to increase INa,L .

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.

The Inhibitory Effects of Ketamine on Human Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels and Action Potential in Rabbit Sinoatrial Node.

AIMS: To investigate the effects of ketamine on human hyperpolarization-activated cyclic nucleotide-gated (hHCN) 1, 2, 4 channel currents expressed in Xenopus oocytes and spontaneous action potentials (APs) of rabbit sinoatrial node (SAN). METHODS: The 2-electrode voltage clamp and standard microelectrode techniques were respectively applied to record hHCN channels currents expressed in Xenopus oocytes and APs of SAN separated from rabbit heart. RESULTS: Ketamine (1-625 µmol/L) blocked hHCN1, 2, and 4 currents with IC50 of 67.0, 89.1, and 84.0 µmol/L, respectively, in a concentration-dependent manner. The currents were rapidly blocked by ketamine and partially recovered after washout. The steady-state activation curves of hHCN1, 2, and 4 currents demonstrated a concentration-dependent shift to the left and the rates of activation were significantly decelerated. But ketamine blocked hHCN channels in a voltage-independence and non-use-dependent manner, and did not modify the voltage dependence of activation and reversal potentials. Furthermore, ketamine suppressed phase-4 spontaneous depolarization rate in isolated rabbit SAN and decreased the beat rates in a concentration-dependent manner. CONCLUSION: Ketamine could inhibit hHCN channels expressed in Xenopus oocytes in a concentration-dependent manner as a close-state blocker and decrease beat rates of isolated rabbit SAN. This study may provide novel insights into other unexplained actions of ketamine.

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.

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.

Performance of field-effect transistors based on Nb(x)W(1-x)S2 monolayers.

The Schottky barrier has been detected in many field-effect transistors (FETs) based on transition metal dichalcogenide (TMD) semiconductors and has seriously affected the electronic properties of the devices. In order to decrease the Schottky barrier in WS2 FETs, novel Nb doping in WS2 monolayers has been performed and p-FETs based on Nb-doped WS2 (Nb(x)W(1-x)S2) monolayers as the active channel have been fabricated for the first time. The monolayer Nb0.15W0.85S2 p-FET has a drain current of 330 µA µm(-1), an impressive I(ON)/I(OFF) of 10(7), and a high effective hole mobility of ∼146 cm(2) V(-1) s(-1). The novel Nb doping in monolayer WS2 has eliminated the ambipolar behavior and reduced the Schottky barrier in WS2 FETs. The reduction of the Schottky barrier is ascribed to the hybridization between W 5d, Nb 4d and S 3p states near the EF and to the enhancement of the metallization of the contact between the Pd metal and monolayer Nb(x)W(1-x)S2 after Nb doping.

Decreased expression of spine-associated Rap guanosine triphosphatase-activating protein (SPAR) in glutamate-treated primary hippocampal neurons.

Spine-associated Rap guanosine triphosphatase-activating protein (SPAR) is an important regulator of activity-dependent remodeling of synapses. It is also critically involved in both mature dendritic spine formation and the maintenance of spine maturity. Glutamate is a major neurotransmitter of the brain, and is involved in all aspects of cognitive function, as it is the primary transmitter utilized by the cortical and hippocampal pyramidal neurons. Glutamate has also been associated with neuronal dendritic spine damage. The precise molecular mechanisms underlying dendritic spine damage following glutamate-induced neurotoxicity remain unknown. In the current study, we measured mRNA and protein expression levels of SPAR and serum-inducible kinase (SNK) in primary hippocampal neurons following glutamate treatment. Expression of SPAR and SNK was altered by glutamate treatment, indicating that the SPAR and SNK signaling pathways may be involved in the damage to dendritic spines in hippocampal neurons following excitotoxicity induced by glutamate.