蝙蝠葛碱对多非利特诱发的早后除极的治疗作用

目的 研究蝙蝠葛碱（Dau）对多非利特(dof) 诱发的早后除极（EADs）的治疗作用和可能机制. 方法 用腹主动脉缩窄法制备家兔心肌肥厚模型; 标准微电极技术记录家兔右心室乳头肌动作电位, 观察1 μmol&#8226;L-1 dof对正常、肥厚、低钾及肥厚＋低钾状态下家兔乳头肌动作电位的影响;诱发出 EADs后, 给予终浓度30 μmol&#8226;L-1 的Dau, 观察Dau对以上不同病理状况下动作电位时程（APD）和EADs的影响. 结果 dof延长家兔乳头肌动作电位, 与正常组比较, 差异有显著性（P<0.05）;低钾和心肌肥厚时家兔乳头肌动作电位较正常家兔明显延长;dof在低钾和心肌肥厚状态下, EADs的发生率分别与正常组、低钾和心肌肥厚组相比均有显著升高;发生EADs后给予Dau, 可明显降低EADs的发生率. 结论 蝙蝠葛碱对EADs具有良好的治疗作用, 机制可能与其对多个离子通道的作用有关.     

Efficacy and safety of dofetilide in patients with atrial fibrillation and atrial flutter

Background  Dofetilide, an I_Kr blocker has been demonstrated to be effective in terminating persistent atrial fibrillation and flutter (AF/AFL), and in maintaining sinus rhythm after direct current cardioversion (CV). It is not known, however, whether pharmacological conversion with dofetilide predicts maintenance of sinus rhythm. In addition, there is limited information comparing the efficacy of dofetilide in persistent versus paroxysmal AF/AFL. Methods and Results  Eighty consecutive patients with AF/AFL (51 persistent, 29 paroxysmal) admitted for initiation of dofetilide were studied. Termination of persistent AF/AFL occurred in 61% of patients while 39% required CV. After 21 ± 19 months of follow-up, 37% of patients with persistent AF/AFL were free of recurrence. Acute conversion with dofetilide did not predict long term efficacy. Dofetilide was more effective in maintaining sinus rhythm in patients with AFL (65%) than in those with AF (25%) (p < 0.05). Dofetilide was more likely to maintain sinus rhythm in patients with persistent than paroxysmal AF/AFL (37 vs. 14%; p < 0.05). Torsades de Pointes developed in two patients despite careful dosing and monitoring of QT changes. Conclusions  Dofetilide is more effective in patients with persistent than in those with paroxysmal AF/AFL. Importantly, short-term response does not necessarily predict long-term efficacy. Significant proarrhythmia can occur even with careful in-hospital monitoring. Dr. Banchs and Dr. Wolbrette contributed equally to this study. Presented in abstract form at the XIII World Congress on Cardiac Pacing and Electrophysiology; December 3, 2007; Rome and published in abstract form (Giornale Italiano di Aritmologia e Cardiostimolazione 2007;10(3):26).     

Class III effects of dofetilide and arrhythmias are modulated by [K+]o in an in vitro model of simulated-ischemia and reperfusion in guinea-pig ventricular myocardium

To evaluate class III effects of clinically relevant concentrations of dofetilide (5 and 10 nmol/l) and the effects of extracellular potassium [K+]o modulation of arrhythmias onset at the level of the "border zone," we used a previously reported in vitro model whereby normoxic and ischemic/reperfused zones were studied. Guinea-pig right ventricular strips (driven at 1 Hz at 36.5+/-0.5 degrees C) were superfused with Tyrode's solution in oxygenated (HCO3- 25 mmol/l, K+ 4 mmol/l, pH 7.35+/-0.05, glucose 5.5 mmol/l: normal zone) and ischemia-simulating conditions (HCO3- 9 mmol/l, pH 6.90+/-0.05, no oxygen and no glucose: altered zone) having either [K+]o 4 (n=20), 8 (n=20) or 12 (n=20) mmol/l. Action potentials in normal and altered zones were recorded simultaneously during 30 min of simulated-ischemia and after 30 min of reperfusion with oxygenated Tyrode's solution. Each preparation served as control for successive phases of dofetilide studies (at 5 and 10 nmol/l) and action potential values were normalized to those present at the beginning of the experiment. During simulated-ischemia, the higher the [K+]o the worse were action potential changes, although full recovery was seen upon 30 min of reperfusion in all [K+]o groups. A high incidence of ischemia/reperfusion arrhythmias was observed in 4 and 12 mmol/l [K+]o groups as opposed to a low incidence of arrhythmias in 8 mmol/l [K+]o group. Dofetilide at 5 and 10 nmol/l with all [K+]o explored: (i) exhibited class III effects, (ii) was effective (or neutral) against ventricular arrhythmias during both simulated-ischemia and reperfusion, and (iii) did not globally increase the dispersion of action potential durations between normal and altered zones. Different arrhythmogenic mechanisms are involved in this model at different [K+]o with 8 mmol/l providing relative protection. Class III effects of dofetilide are evident in the normal zone when in the ischemic-like zone [K+]o ranges from 4 to 12 mmol/l. Thus dofetilide did not increase dispersion of repolarization and had either an antiarrhythmic or a neutral effect during ischemia/reperfusion.     

Dofetilide Enhances the Contractility of Rat Ventricular Myocytes via Augmentation of Na+–Ca2+ Exchange

Purpose  Dofetilide (DOF), a novel Class III antiarrhythmic drug, prolongs the action potential duration (APD) and shows a positive inotropic effect in guinea pig papillary muscle. The present experiments were designed to study the positive inotropic effect of DOF on rat ventricle and explore its possible mechanism(s). Methods  Hearts from male Wistar rats (260–320 g) were divided into five groups and perfused in Langendorff mode. Ventricular myocytes were enzymatically isolated from male Wistar rats. Whole-cell voltage-clamping technique was used to test the Na⁺–Ca²⁺ exchange (NCE) current (I _NCX); Calcium transients and cell shortening provoked by field stimulation or using calcium current command waveform were observed synchronously with an ionic imaging system. Results  DOF (0.03–1.0 μM) increased left ventricular function in isolated rat hearts in a concentration-dependent manner. DOF (0.03–1.0 μM) also concentration-dependently increased both inward and outward I _NCX in isolated rat ventricular cells. The EC₅₀ values of DOF were 0.149 μM for the inward I _NCX and 0.249 μM for outward I _NCX, respectively. DOF 0.2 μM significantly enhanced Ca²⁺ transient and cell shortening in single rat ventricular myocytes driven by field electric stimulation. When the patch clamp system was connected to the ionic imaging system, Ca²⁺ current (I _Ca), Ca²⁺ transient and cell shortening amplitude in a same cell were recorded synchronously. Application of DOF 0.2 μM had no effect on I _Ca, but significantly increased Ca²⁺ transient and cell shortening. NCX inhibitor KB-R7943 0.6 μM significantly depressed the effects of DOF on Ca²⁺ transient and cell shortening. Conclusions  We conclude that DOF enhanced contractility of rat ventricular myocytes. The enhancement of NCE may be involved in the positive inotropic action of DOF.     

Pro- and antiarrhythmic effects of fast cardiac pacing in a canine model of acquired long QT syndrome

Increasing the heart rate is one option for suppressing bradycardia-dependent polymorphic ventricular tachycardias (PVTs). The mechanisms underlying preventive pacing in acquired forms of the long QT syndrome (LQTs) are still not fully understood. Using two needle electrodes, local effective refractory periods (ERPs) were determined in the left (LV) and right ventricle (RV) in 20 dogs with acute AV node ablation before continuous pacing, during a 20-min period of continuous fast pacing (Cl 300 ms, fastpac) and during a 35-min recovery period with slow (Cl 500 ms) pacing. This protocol was applied to control dogs (5 dogs) and dogs with pretreatment of the IKs blocking agent chromanol 293b (5 dogs, LQTs1), the IKr-blocking agent dofetilide (5 dogs, LQTs2) or a combination thereof (5 dogs). Fastpac resulted in a significant abbreviation of ERPs in control dogs and dogs receiving dofetilide or chromanol 293b. During recovery, shortening of ERPs persisted in the control group, but diminished in dogs with acquired LQTs. In dogs with LQTs2 fastpac could not suppress inhomogeneity of refractoriness during recovery. With pretreatment of dofetilide and chromanol 293b in combination, MAP duration during fastpac significantly increased (first beat: 256±6 ms vs. sixth beat: 278±9 ms, p<0.05) and fastpac-induced PVTs were evident. ERP shortening and reduced inhomogeneity of refractoriness might be one antiarrhythmic action of fastpac in dogs with acute AV-block. However, in the acquired LQTs1 and 2 beneficial effects of fastpac diminished and in a combination thereof fastpac-induced PVTs are likely.     

多非利特合成工艺的研究

目的合成多非利特及其几个关键中间体。方法本文以苯乙胺为原料经过一系列的硝化、溴乙基化、缩合、甲基化等反应制备多非利特。结果及结论此合成路线原料易得,工艺可行。     

Gastrointestinal-tract models and techniques for use in safety pharmacology

Introduction: The human ether-a-go-go-related gene (hERG) encodes a potassium channel responsible for the cardiac delayed rectifier current (I_Kr) involved in ventricular repolarization. Drugs that block hERG have been associated with QT interval prolongation and serious, sometimes fatal, cardiac arrhythmias (including torsade de pointes). While displacement of [³H]dofetilide, a potent methanesulfonanilide hERG blocker, from cells heterologously expressing hERG has been suggested as a screening assay, questions have been raised about its predictive value.Methods: To validate the utility of this assay as a screening tool, we performed a series of saturation and competition binding studies using [³H]dofetilide as ligand and either intact cells or membrane preparations from HEK 293 cells stably transfected with hERG K⁺ channels. The object of these experiments was to (1) compare binding K_i values for 22 hERG blockers using intact cells or membrane homogenates to determine whether maintaining cell integrity enhanced assay reliability; (2) evaluate the ability of different K⁺ concentrations (2, 5, 10, 20, and 60 mM) to modulate hERG binding; and (3) to establish the predictive value of the assay by comparing K_i values from binding studies at 5 and 60 mM [K⁺]_o to functional IC₅₀ values for hERG current block using 56 structurally diverse drugs.Results: We found (a) comparable K_i values in the intact cell and isolated membrane binding assays, although there were some differences in rank order; (b) increasing [K⁺]_o lowered the K_d and increased the B_max for [³H]dofetilide, particularly in the membrane assay; and (c) good correlation between binding K_i values and functional IC₅₀ values for hERG current block.Discussion: In conclusion, increasing K⁺ concentrations results in an increase in both [³H]dofetilide affinity for hERG and available binding sites, particularly when using membrane homogenates. There are no meaningful differences between K_i values when comparing intact cell versus membrane assay, neither are there meaningful trends with increasing [K⁺]_o within assays. There is good correlation between binding K_i values and functional (whole-cell patch clamp) IC₅₀ values at both 5 and 60 mM K⁺ concentrations (R² values of .824 and .863, respectively). The simplicity, predictability, and adaptability to high-throughput platforms make the [³H]dofetilide membrane binding assay a useful tool for screening and ranking compounds for their potential to block the hERG K⁺ channel.