Melatonin inhibits arrhythmias induced by increased late sodium currents in ventricular myocytes / 药学学报

Melatonin (Mel) has been shown to have cardioprotective effects, but its action on ion channels is unclear. In this experiment, we investigated the inhibitory effect of Mel on late sodium currents (INa.L) in mouse ventricular myocytes and the anti-arrhythmic effect at the organ level as well as its mechanism. The whole-cell patch clamp technique was applied to record the ionic currents and action potential (AP) in mouse ventricular myocytes while the electrocardiogram (ECG) and monophasic action potential (MAP) were recorded simultaneously in mouse hearts using a multichannel acquisition and analysis system. The results demonstrated that the half maximal inhibitory concentration (IC50) values of Mel on transient sodium current (INa.T) and specific INa.L opener 2 nmol·L-1 sea anemone toxins II (ATX II) increased INa.L were 686.615 and 7.37 μmol·L-1, respectively. Mel did not affect L-type calcium current (ICa.L), transient outward current (Ito), and AP. In addition, 16 μmol·L-1 Mel shortened ATX II-prolonged action potential duration (APD), suppressed ATX II-induced early afterdepolarizations (EADs), and significantly reduced the incidence of ventricular tachycardia (VT) and ventricular fibrillation (VF) in Langendorff-perfused mouse hearts. In conclusion, Mel exerted its antiarrhythmic effects principally by blocking INa.L, thus providing a significant theoretical basis for new clinical applications of Mel. Animal welfare and experimental process are in accordance with the regulations of the Experimental Animal Ethics Committee of Wuhan University of Science and Technology (2023130).

Ações Transmurais Inotrópicas e Antiarrítmicas da Ranolazina em um Modelo Celular da Síndrome do QT Longo Tipo 3 / Inotropic and Antiarrhythmic Transmural Actions of Ranolazine in a Cellular Model of Type 3 Long QT Syndrome

Resumo A Ranolazina (RANO), conhecida na clínica como Ranexa, é um fármaco que previne a arritmia cardíaca através da inibição da corrente de sódio tardia (INaT). Um gradiente de voltagem transmural do canal Nav1.5 encontra-se na parede ventricular esquerda do coração. Assim, investigamos os efeitos da RANO em cardiomiócitos saudáveis e em modelo celular da Síndrome do QT longo tipo 3 (SQTL tipo 3). Usamos células isoladas do endocárdio (ENDO) e do epicárdio (EPI) e um software de medição com detecção de bordas por vídeo e microscopia de fluorescência para monitorar os transientes de cálcio. A RANO (0,1, 1, 10 e 30 uM, a 25OC) em uma série de frequências de estimulação teve impacto pouco significativo sobre ambos os tipos de células, mas a RANO (30uM) a 35OC minimizou o encurtamento dos sarcômeros em ~21% para células do endocárdio. Em seguida, para simular a SQTL tipo 3, as células do ENDO e EPI foram expostas à toxina ATX-II da anêmona do mar, que aumenta a INaT. As arritmias celulares induzidas por ATX-II foram suprimidas com o uso da RANO (30 µM) a 35OC. Com base nesses resultados, podemos concluir que a RANO tem um impacto pouco significativo sobre o encurtamento dos sarcômeros de células saudáveis do ENDO e EPI. Além disso, ela suprime as arritmias induzidas por INaT para níveis semelhantes nas células do ENDO e EPI.

Abstract Ranolazine (RANO) prevents cardiac arrhythmia by blocking the late sodium current (INaL). A transmural gradient of Nav1.5 is found in the left ventricular wall of the heart. Thus, we investigated the effects of RANO in healthy cardiomyocytes and in a cellular model of type 3 long QT syndrome (LQT3). We used isolated endocardium (ENDO) and epicardium (EPI) cells and a video edge detection system and fluorescence microscopy to monitor calcium transients. RANO (0.1, 1, 10 and 30 uM, at 25oC) at a range of pacing frequencies showed a minor impact on both cell types, but RANO at 30uM and 35oC for ENDO cells attenuated sarcomere shortening by~21%. Next, to mimic LQT3, we exposed ENDO and EPI cells to anemone toxin II (ATX-II), which augments INaL. Cellular arrhythmias induced by ATX-II were abrogated by RANO (30 µM) at 35oC. Based on our results we can conclude that RANO has a minor impact on sarcomere shortening of healthy ENDO and EPI cells and it abrogates arrhythmias induced by INaLto a similar level in ENDO and EPI cells.

Effect of Ca2+/calmodulin-dependent protein kinaseⅡinhibitor KN-93 on late sodium current in rabbits model of heart failure / 中国病理生理杂志

AIM:To investigate the change of late sodium current (INaL) and the effect of Ca2+/calmodulin-dependent protein kinaseⅡ (CaMKⅡ) inhibitor KN-93 on INaLin the cardiomyocytes after isoproterenol-induced heart fai-lure (HF) in rabbits. METHODS:The rabbit model of HF was induced by injecting isoproterenol (300 μg·kg-1· d-1) for 15 d. One month later, all rabbits received by echocardiography and HE staining to observe the morphological changes of myocardium for evaluating the HF model. The protein expression of NaV1.5, CaMKⅡδ and phosphorylated CaMKⅡδ was determined by Western blot. The ventricular myocytes were isolated from the rabbits of normal saline(NS) group and HF group by Langendorff perfusion, and the whole-cell patch-clamp technique was used to record INaL. RE-SULTS:Compared with NS group,the heart rate in HF group was increased (P<0.01), the ventricular cavity was en-larged (P<0.05),and the cardiac function was decreased(P<0.01). Compared with NS group,the cardiomyocytes in HF group arranged in disorder, vacuolar degeneration and myocardial interstitial edema were observed, and fibrous tissue increased. The protein levels of NaV1.5,CaMKⅡδ and phosphorylated CaMKⅡδ in HF group were higher than those in NS group(P<0.01). INaLin HF group significantly increased compared with NS group (P<0.01). After adding sea anemone toxin Ⅱ (ATXⅡ), the density of INaLin HF group and NS group was significantly increased, but that in HF group increased more obviously than that in NS group (P<0.01). After ATXⅡ had induced stable current, we added KN-93 into NS group and HF group,and we found that the ATXⅡ-increased INaLin NS group and HF group was signifi-cantly decreased(P<0.05).CONCLUSION:CaMKⅡinhibitor KN-93 inhibits the increase in INaLin HF rabbits,which may be related to the activity of CaMKⅡδ and the regulation of CaMKⅡ δ on INaL.

Type 2 Diabetes Induces Prolonged P-wave Duration without Left Atrial Enlargement

Prolonged P-wave duration has been observed in diabetes. However, the underlying mechanisms remain unclear. The aim of this study was to elucidate the possible mechanisms. A rat model of type 2 diabetes mellitus (T2DM) was used. P-wave durations were obtained using surface electrocardiography and sizes of the left atrium were determined using echocardiography. Cardiac inward rectifier K+ currents (I(k1)), Na+ currents (I(Na)), and action potentials were recorded from isolated left atrial myocytes using patch clamp techniques. Left atrial tissue specimens were analyzed for total connexin-40 (Cx40) and connexin-43 (Cx43) expression levels on western-blots. Specimens were also analyzed for Cx40 and Cx43 distribution and interstitial fibrosis by immunofluorescent and Masson trichrome staining, respectively. The mean P-wave duration was longer in T2DM rats than in controls; however, the mean left atrial sizes of each group of rats were similar. The densities of I(k1) and I(Na) were unchanged in T2DM rats compared to controls. The action potential duration was longer in T2DM rats, but there was no significant difference in resting membrane potential or action potential amplitude compared to controls. The expression level of Cx40 protein was significantly lower, but Cx43 was unaltered in T2DM rats. However, immunofluorescent labeling of Cx43 showed a significantly enhanced lateralization. Staining showed interstitial fibrosis was greater in T2DM atrial tissue. Prolonged P-wave duration is not dependent on the left atrial size in rats with T2DM. Dysregulation of Cx40 and Cx43 protein expression, as well as fibrosis, might partly account for the prolongation of P-wave duration in T2DM.

Antiarrhythmic ionic mechanism of Guanfu base A--Selective inhibition of late sodium current in isolated ventricular myocytes from guinea pigs / 中国天然药物

The present study was designed to determine the effects of Guanfu base A (GFA) on the late sodium current (INa.L), transient sodium current (INa.T), HERG current (IHERG), and Kv1.5 current (IKv1.5). The values of INa.L, INa.T, IHERG and IKv1.5 were recorded using the whole-cell patch clamp technique. Compared with other channels, GFA showed selective blocking activity in late sodium channel. It inhibited INa.L in a concentration-dependent manner with an IC50 of (1.57 ± 0.14) μmol · L(-1), which was significantly lower than its IC50 values of (21.17 ± 4.51) μmol · L(-1) for the INa.T. The inhibitory effect of GFA on INa,L was not affected by 200 μmol · L(-1) H2O2. It inhibited IHERG with an IC50 of (273 ± 34) μmol · L(-1) and has slight blocking effect on IKv1.5, decreasing IKv1.5 by only 20.6% at 200 μmol · L(-1). In summary, GFA inhibited INa.L selectively and remained similar inhibition in presence of reactive oxygen species. These findings may suggest a novel molecular mechanism for the potential clinical application of GFA in the treatment of cardiovascular disorders.

Effect of Ivabradine Prolonging the Cardiac Action Potential Duration With its Proarrhythmic Action in Experimental Rabbitin vitro / 中国循环杂志

Objective: To observe the effect of ivabradine (IVA) on atrial and ventricular monophasic action potential duration (MAPD) and its proarrhythmic action at presence of sea anemone toxin-II (ATX-II) in isolated rabbit heart modelin vitro. Methods: The perfusion of isolated heart from female New Zealand white rabbit was conducted by Langendorff method in vitro. Left atrial and left ventricular endo- , epi-cardial action potential were recorded when pacing with ifxed frequency of 350 ms (in correspondence with the heart rate of 171 times/min) to observe the effect of IVA alone and ATX-II (3 nmol/L) with IVA on MAPD90. In addition, to observe the action of IVA alone and ATX-II with IVA on proarrhythmia when IVA reducing the heart rate to autonomous cardiac rhythm as (156±10) times/min. Results: IVA at (3-10) μmol/L prolonged atrial and ventricular endo- , epi-cardial MAPD90 by (15.9 ± 2.0) ms, (31.5 ± 4.0) ms and (23.9 ± 3.0) ms (n=6,P<0.01), respectively. ATX-II at 3 nmol/L prolonged atrial and ventricular MAPD90 by (36.5 ± 5.0)ms and (19.9 ± 3.0) ms, (19.5 ± 4.0) ms (n=6,P<0.01) respectively. With ATX-II treatment, IVA at (6-10) μmol/L decreased atrial MAPD90 by (14.4 ± 4.0) ms (n=6,P<0.01), it induced atrial arrhythmia. With 3 nmol/L of ATX-II treated ventricle, IVA at (3-10) μmol/L obviously prolonged endo- and epi-cardial MAPD90 by (36.2 ± 7.0) ms and (27.5 ± 5.0) ms(n=6,P<0.01), respectively. IVA didn’t increase ventricular beat-to-beat variability and transmural dispersion of MAPD90 no matter with or without ATX-II treatment, no ventricular arrhythmia occurred. Conclusion: IVA prolongs both atrial and ventricular MAPD, with increased late sodium current, IVA may induce atrial arrhythmia but not ventricular arrhythmia in experimental rabbits in vitro.

Effects of Propafenone on Action Potential of Rabbit Ventricular Myocytes and the Use-dependent Block of Transient Sodium Current / 中国循环杂志

Objective: To study the effects of propafenone on action potential (AP) of rabbit ventricular myocytes with the tonic block and use-dependent block of transient sodium current (INa-T). Methods: A total of 10 adult New Zealand white rabbits were sacriifced and 10 individual ventricular myocytes were isolated by enzyme digestion method. Microelectrode technologies were used to record AP-related parameters: maximum diastolic potential (MDP), maximum rate of rise of the action potential upstroke (Vmax), action potential amplitude (APA) and action potential duration at 20%, 50% and 90% (APD20, APD50 and APD90).INa-T was measured, I-V curves and peak currents at different frequencies were detected by whole cell patch clamp before and after propafenone perfusion at 10 μmol/L. Results: There was no statistical difference in MDP at before and after propafenone perfusion as (-80 ± 6) mV vs (-82 ± 5) mV,P>0.05. After perfusion, APA was signiifcantly decreased as (95 ± 12) mV vs ( 125 ± 10) mV,P0.05, (16 ± 3) ms vs (12 ± 3) ms,P>0.05 and (86 ± 14) ms vs (85 ± 12) ms,P>0.05. After propafenone perfusion, I-V curve ofINa-T was shifted upward and the peak current was decreased as (3001 ± 383) pA vs (4193 ± 378) pA, P0.05. After perfusion, no significant use-dependent block was observed when stimulated at 0.06 Hz and 1 Hz,P>0.05, while at 2 Hz, 5 Hz and 10 Hz, propafenone perfusion demonstrated signiifcant use-dependent block uponINa-T with the inhibition fractions of (22 ± 11)%, (38 ± 14)% and (52 ± 17)% respectively, those were signiifcantly different from the inhibition fractions at either 0.06 Hz or 1Hz,P<0.05. When the inhibition fractions were compared by each 2 conditions, allP<0.05. Conclusion: Propafenone may slow down the Vmax of AP, reduce APA and without the impact on APD; the effects onINa-T is not only in tonic block, but also more obviously in use-dependent block in isolated ventricular myocytes of New Zealand rabbit. Such inlfuences minimized the impact on QT interval and meanwhile, decreased the incidence of brad arrhythmia.

The Effects and Mechanism of Lidocaine on Evoked-Bursting Firing of Injured Dorsal Root Ganglion Neurons / 天津医药

Objective To study the effects and current mechanism of low concentration of lidocaine on evoked-bursting (EB) firing of dorsal root ganglion (DRG) neurons in rat model of chronic compression (CCD) of DRG . Methods Twenty-four SD rats were divided into normal control group (n=12) and CCD model group (n=12). CCD group was treated with chronic oppression on L4 and L5 DRG with L shape bar. Normal control group received no treatment. In vivo intracellu?lar recording was used to record the incidence of EB and the effect of lidocaine on subthreshold membrane potential oscilla?tion (SMPO). Patch clamp recording was used to record the effect of lidocaine on persistent sodium current (INaP). Results The incidence of EB increased in CCD group( 45.97%, 57/124), which was significantly different when compared with nor?mal group (χ2=26.810, P<0.01). The magnitude of SMPO, INaP and EB were inhibited in a reversible way by lidocaine (50μmol/L). Conclusion The low concentration of lidocaine might play an analgesic effect in peripheral nervous system by se?lectively inhibiting INap, which participates in SMPO formation.

Effect of ranolazine on the fast sodium channel current in rabbit atrial myocytes and use-dependent blockade / 西安交通大学学报(医学版)

Objective To explore the effect of ranolazine on the fast sodium channel current (INa) in rabbit atrial myocytes and the existence of use-dependent blockade. Methods Standard whole cell patch clamp technique was used to study the effect of ranolazine on the fast sodium channel current and the use-dependent blockade caused with different frequencies (1Hz, 3.3Hz and 5Hz) to stimulate the cells. Results The 30μmol/L ranolazine significantly reduced INa with an IC_(50) value of (25.6±1.8)μmmol/L and produced a frequency-dependent inhibitory effect on INa with obvious use-dependence. Conclusion Ranolazine can inhibit the fast sodium channel current in rabbit atrial myocytes and indeed has a use-dependent effect.

Effect of dipfluzine on sodium current in guinea-pig ventricular myocytes / 中国药理学与毒理学杂志

AIM To investigate effect of dipfluzine on sodium current (INa+) in isolated single guinea-pig ventricular myocytes. METHODS INa+ was measured by whole cell patch-clamp technique in single isolated guinea-pig ventricular myocytes which were prepared by enzymatic dissociation method. RESULTSCardiac INa+ was elicited by 50-ms pulses to +50 mV from holding potential at -80 mV with a step of +10 mV, which could be blocked completely by tetrodotoxin 10 μmol·L-1. The peak INa+ occurred at about -20 mV and the reversal potential for INa+ was about +30 mV. Dipfluzine inhibited cardiac INa+ in a concentration-dependent manner. The blocking effect of dipfluzine on INa+ was reversible. Dipfluzine suppressed cardiac INa+, without modifying maximum activation potential and reversal potential. The peak of INa+ was decreased by about 46% at -20 mV and shape of I-V curve was not altered by dipfluzine 40 μmol·L-1. Dipfluzine shifted the steady-state inactivation curve of INa+ towards more negative without changing the slope factor and produced very little change in the steady-state activation curve towards more positive. The mean half activation voltage was (-34.9±5.1) mV and slope factor was (6.0±4.8) mV under control condition and (-33.7±3.6) mV and (5.6±2.4) mV following exposure to dipfluzine 40 μmol·L-1. The half inactivation voltage was (-73.0±4.6)mV and slope factor was (4.8±1.8)mV under control condition and (-82.8±7.2)mV and (4.8±1.8)mV following dipfluzine 40 μmol·L-1 treatment. Dipfluzine delayed recovery of cardiac INa+ from inactivation state. The time course of recovery was (36±11) ms in control group and (79±28) ms in dipfluzine 40 μmol·L-1 group. CONCLUSION Dipfluzine inhi- bits cardiac INa+ in a concentration-dependent manner and has higher affinity for the inactivated state than that for resting state of Na+ channels.

Effect of Anlv Capsule on sodium ion channels in ventricular myocytes of guinea pig / 中华中医药杂志

Objective:To observe the effect of Aalv Capsule on sodium current in guinea pig ventricular myocytes(INa)for exploring the mechanism of its anti-premature beats.Methods:Whole-cell patch-clamp recording technique was used to record the Aalv Capsule for a single cell of sodium currents in guinea pig ventricular myocytes.Results:There was dose-dependent of Aalv Capsule in block of sodium currents and had a certain amount of use-dependent and time-dependent.Conclusion:The role of Aalv Capsule in blocking sodium current block was one of the mechanisms of its in bearing premature.

The effects of pain-producing agents on the voltage-dependent ionic channels of rat trigeminal ganglion

Voltage-Dependent Sodium And Potassium Currents In Acutely Isolated Rat Trigeminal Caudal Neurons

Effects of droperidol on the enhancement of persistent sodium currents induced by in vitro ischemia-like condition in isolated rat CA1 paramidal neurons / 中国临床药理学与治疗学

AIM: To study the effects of droperidol on the enhancement of persistent sodium currents induced by in vitro ischemia-like condition in isolated rat CA1 paramidal neurons. METHODS: Whole-cell patch-clamp recordings were made from enzymatically isolated rat CA1 hippocampal paramidal neurons. Ischemia was induced by oxygen and glucose deprivation. RESULTS: All of 3, 10 ,and 30 ?mol?L -1 of droperidol significantly inhibited the enhancement of persistent sodium currents induced by ischemia, but the different concentrations did not show significant difference. CONCLUSION: Droperidol in clinical concentration can inhibit the enhancement of persistent sodium current induced by ischemia.

Effect of hypoxia on persistent sodium current in ventricular myocytes from 3-week infarcted rat heart / 中国病理生理杂志

AIM: To investigate the effect of hypoxia on persistent sodium current (I_Nap ) in single ventricular myocyte isolated from acute myocardial infarction (AMI) heart of rats and to study the mechanisms of cardiac arrhythmias that occur after AMI. METHODS: AMI model was induced by ligating the left anterior descending coronary artery in rats. The whole-cell patch clamp technique was used to record the current in epicardial myocytes in infarcted region from rats at 3 week after AMI. RESULTS: In normoxic conditions, the current density of I_ Nap in cardiomyocytes of fake operation (FO) and AMI hearts was 0.144?0.022 pA/pF (n=9), 0.121?0.013 pA/pF (n=9,P