苄基四氢巴马汀对卵母细胞膜Kv1.2通道的作用

目的:研究苄基四氢巴马汀(BTHP)抗心律失常作用的分子机制。方法:比较BTHP和经典Ⅲ类抗心律失常药胺碘酮对卵母细胞膜上表达的Kv1.2通道的外向钾电流的阻滞作用。结果:BTHP和胺碘酮对Kv1.2通道的外向钾电流均有阻滞作用,在10-3～10mmol/L浓度范围内,对电流的阻滞作用增强,二者相比,差异无统计学意义。结论:BTHP能够阻滞Kv1.2通道的外向钾电流,这是其抗心律失常作用的分子机制之一。     

胺碘酮治疗室性心律失常临床观察

胺碘酮为广谱抗心律失常药,主要通过抑制电压依赖性钾通道,使外向钾电流受抑,动作电位和有效不应期延长,从而起到抗心律失常的作用,多用于室上性和室性快速心律失常的治疗。现归纳总结我院应用胺碘酮治疗室性心律失常的经验。     

阿魏酸钠对家兔心室肌细胞钾通道电流的影响

目的:探讨阿魏酸钠对家兔心室肌细胞膜延迟整流钾电流快速与缓慢激活成分(IKr、IKs)、内向整流钾电流(IK1)、瞬时外向钾电流(Ito)的影响.方法:酶解法分离单个家兔心室肌细胞,以经典的Ⅲ类药胺碘酮为对照,采用全细胞膜片钳技术记录浓度为3.0、10.0、30.0,100.0 μmol/L的阿魏酸钠对IKr,IKs、IK1、Ito的作用.结果:阿魏酸钠的作用弱于胺碘酮,二者均可浓度依赖性抑制IKr、ILs时间依赖性外向电流及尾电流(IKr,tail、IKs,tail).不同浓度的阿魏酸钠对IKr,tail的抑制率为:(12.1±2.5)%、(24.1±3.0)%、(47.0±5.8)%及(58.5±8.3)%(n=5,P＜0.05);对IKs,tail的抑制率为:(15.6±6.4)%、(27.1±6.5)%、(45.6±5.8)%及(51.8±6.6)%(n=5,P＜0.05),其对IKr,tail及IKs,tail的半数抑制浓度(IC50)均大于胺碘酮(43.6:3.48 μmol/L,44.9:5.11 μmol/L).30.0、100.0 μmol/L阿魏酸钠及10.0、30.0 μmol/L胺碘酮可使IK1的I-V曲线左移,在-100 mV及-20 mV测试电压下,阿魏酸钠对IK1内向、外向电流抑制率小于胺碘酮(n=5,P＜0.05).阿魏酸钠与胺碘酮均不影响Ito及其I-V曲线.结论:阿魏酸钠复合阻滞复极期多种钾电流,可能是其抗心律失常作用的电生理机制之一.     

胺碘酮的临床应用进展

胺碘酮起初是作为冠状动脉扩张剂治疗心绞痛而问世。2 0世纪 70年代发现其有很强的抗心律失常作用 ,且用于抗心律失常的治疗取得了较好疗效。但由于早期用药剂量较大 ,导致较多副作用 ,故其临床应用曾一度受到限制。 90年代著名的 CAST结果公布 ,胺碘酮作为抗心律失常药物重新成为研究热点。1　电生理作用胺碘酮为苯呋喃类衍生物 ,结构中含有两个碘分子 ,具有下列电生理作用 [1 ] :1阻断钾通道 :阻断、延迟整流外向钾电流 (Ik) ,从而使心房和心室的肌纤维动作电位时程 (APD)延长。 2轻度阻断钠通道 :阻断失活态钠通道 ,有利于快速心律失…     

阿魏酸钠与胺碘酮对家兔心室肌细胞L型钙通道电流的影响

目的探讨阿魏酸钠对家兔心室肌细胞膜L型钙通道电流(ICa-L)的影响。方法酶解法急性分离兔单个心室肌细胞,以经典的Ⅲ类抗心律失常药物胺碘酮为对照,应用膜片钳全细胞记录技术观察3,10,30,100μmol/L的阿魏酸钠对心室肌细胞膜ICa-L的作用。结果阿魏酸钠及胺碘酮均呈浓度依赖性抑制L型钙电流。3,10,30,100μmol/L的阿魏酸钠对ICa-L的抑制率分别为11.1%±2.4%,26.9%±6.2%,40.5%±5.0%,61.9%±5.5%(P<0.05);1,3,10,30μmol/L的胺碘酮对ICa-L的抑制率分别为21.1%±3.8%,32.6%±2.6%,52.6%±4.6%,71.4%±7%(P<0.05);半数抑制浓度分别为32.6及9.5μmol/L,阿魏酸钠的抑制作用弱于胺碘酮(P<0.05)。阿魏酸钠及胺碘酮均能使ICa-L电流-电压曲线上移,稳态激活曲线右移,失活曲线左移,并可减慢钙通道灭活后的恢复过程。结论阿魏酸钠对ICa-L具有浓度依赖性阻滞作用,使ICa-L的激活减慢,失活加快,并且失活后的恢复时间延长,可能是其抗心律失常作用的电生理机制之一。     

胺碘酮在心肌梗死后病人中的应用

室性心律失常是心脏猝死的独立预测因素,特别是在心肌梗死(MI)后第一年。最近,胺碘酮成为一种有希望的抗心律失常药。胺碘酮属Ⅲ类药物,影响动作电位时限及不应期。此药主要阻滞失活的钠通道,也阻滞慢内向钙流。胺碘酮还可抑制ATP敏感的钾通道,可减少缺血期室性心律失常的发生。此外,还具有抗交感神经及抗甲状腺功能,有利     

普罗帕酮对Kv1.4ΔN钾通道的作用及细胞外钾离子和pH浓度变化时的影响

目的:探讨抗心律失常药物普罗帕酮对Kv1.4△N钾通道的作用,以及细胞外钾离子和pH浓度变化时对该作用的影响,并探讨该作用可能的机制.方法:将Kv1.4ΔN的mRNA注射入非洲爪蟾卵母细胞并使用双电极钳制法观察普罗帕酮对Kv1.4ΔN电生理特性的影响,以及细胞外钾离子和pH变化时的电生理特性改变.结果:pH7 4状态下,普罗帕酮对Kv1.4ΔN通道的峰电流有抑制作用,这种阻滞作用具有电压依赖性、浓度依赖性以及频率依赖性,并且随电位的升高而作用加强,符合单指数和线性关系.普罗帕酮加速电流的失活过程.在不同的钾离子浓度下,这种阻滞作用具有pH依赖性,细胞外高钾pH7 4时,不同浓度普罗帕酮灌流显示IC50为121 μmol/L;细胞外酸性环境下(pH6 0)IC50提高到463 μmol/L,碱性化的环境(pH8 0)降至58 μmol/L.结论:普罗帕酮是Kv1.4ΔN的阻滞剂,可能与作用于细胞内的某些位点有关.     

Kv1.5钾通道与心房颤动

心房颤动是最为常见的心律失常之一。尽管目前有很多药物正应用于心房颤动的治疗,如多非利特、胺碘酮、索他洛尔、普罗帕酮、氟卡尼等,但是人们仍然希望得到一种更为安全有效的抗心律失常药物。理想的治疗心房颤动的药物应是具有高度的心房肌细胞选择性,可以终止或延缓心房颤动的发生,而没有延长Q-T间期或负性肌力的作用。电压门控钾离子通道Kv1.5被认为是实现心房高度选择性理想的药物作用靶点。临床及动物研究证实,Kv1.5钾通道是心房电重构的基础,其阻滞剂可以选择性延长心房有效不应期而终止心房颤动。本文旨在对Kv1.5钾通道的历史、结构、功能和最新的一些阻滞剂做一综述。     

参松养心胶囊对Kv1.4钾电流特性的影响

目的: 探讨中药复方制剂参松养心胶囊对KV1.4钾通道C型(KV1.4△N)失活的影响。方法: 将Kv1.4ΔN mRNA注射入非洲爪蟾卵母细胞中,使用双电极钳制法（Two electrodes voltage clamp TEV）观察参松养心胶囊对KV1.4ΔN电生理特性的影响 。结果: 参松养心胶囊对Kv1.4ΔN通道的峰电流有抑制作用,这种阻滞作用具有电压依赖性,随电位的升高而作用加强,符合单指数和线性关系。参松养心胶囊可加速KV1.4ΔN钾通道电流的失活过程,同时可使KV1.4ΔN通道失活后的恢复减慢 。结论: 参松养心胶囊能显著抑制KV1.4钾通道电流,这可能是其抗心律失常作用的机制之一。     

心力衰竭兔左室Ito、Ik1通道蛋白表达变化及比索洛尔干预作用

目的观察心力衰竭兔左室心肌细胞Ito、Ik1通道蛋白表达变化及比索洛尔的干预作用,探讨心力衰竭时室性心律失常的发生机制及比索洛尔可能的抗心律失常机制。方法 39只新西兰兔随机分为假手术组(SO)、心力衰竭组(HF)及比索洛尔干预组(BF),以容量负荷联合压力超负荷方法构建心力衰竭兔模型,评价模型成功后,予比索洛尔干预6周;用Westernblot法测定瞬时外向钾电流(Ito)、内向整流钾电流(Ik1)通道蛋白的表达水平。结果①HF组兔心动超声示左房、左室增大,心脏收缩功能和舒张功能减低,BNP水平明显升高,心体比明显增大;比索洛尔干预6周可部分逆转上述变化;②与SO组相比,心力衰竭时左室心肌细胞Kv4.3(介导Ito,f)、Kv1.4(介导Ito,s)及Kir2.1(介导Ik1)蛋白表达水平降低;比索洛尔干预6周后Kv4.3、Kv1.4、Kir2.1蛋白表达较心力衰竭组均有所增加。结论心力衰竭兔左室心肌细胞Kv4.3、Kv1.4、Kir2.1蛋白表达明显下降,可能是心力衰竭时室性心律失常发生的分子基础。比索洛尔干预后可部分逆转Kv4.3、Kv1.4、Kir2.1蛋白表达的下调,可能是其抗心律失常的分子机制。     

Ultra-rapid delayed rectifier channels: molecular basis and therapeutic implications

The ultrarapid delayed rectifier channels have attracted considerable interest as targets for 'atrial-selective' antiarrhythmic drugs because they contribute to atrial but not to ventricular repolarization. Thus, I(Kur) channel blockers are expected to prolong selectively the atrial effective refractory period without inducing proarrhythmic effects due to excessive ventricular action potential prolongation. Here we provide an overview of the properties of I(Kur) channels in expression systems and native cardiomyocytes. The ion conducting pore of the channel is formed by four Kv1.5 α-subunits, whereas the ancillary β-subunits Kvβ1.2, Kvβ1.3, and Kvβ2.1 control channel trafficking and plasma membrane integration as well as activation and inactivation kinetics. Investigation of I(Kur) channel blockers in cardiomyocytes is complicated (i) by substantial overlap of I(Kur) with other currents, notably the transient outward current I(to), (ii) by lack of drug selectivity, and (iii) by disease-induced regulation of I(Kur). Some new compounds developed as I(Kur) blockers are described and their efficacy in treatment of atrial fibrillation (AF) is discussed. Current evidence suggests that pure I(Kur) channel block may not be sufficient to suppress AF.     

Extracellular acidosis modulates drug block of Kv4.3 currents by flecainide and quinidine

INTRODUCTION: As a molecular model of the effect of ischemia on drug block of the transient outward potassium current, the effect of acidosis on the blocking properties of flecainide and quinidine on Kv4.3 currents was studied. METHODS AND RESULTS: Kv4.3 channels were stably expressed in Chinese hamster ovary cells. Whole-cell, voltage clamp techniques were used to measure the effect of flecainide and quinidine on Kv4.3 currents in solutions of pH 7.4 and 6.0. Extracellular acidosis attenuated flecainide block of Kv4.3 currents, with the IC50 for flecainide (based on current-time integrals) increasing from 7.8 +/- 1.1 microM at pH 7.4 to 125.1 +/- 1.1 microM at pH 6.0. Similar effects were observed for quinidine (IC50 5.2 +/- 1.1 microM at pH 7.4 and 22.1 +/- 1.3 microM at pH 6.0). Following block by either drug, Kv4.3 channels showed a hyperpolarizing shift in the voltage sensitivity of inactivation and a slowing in the time to recover from inactivation/block that was unaffected by acidosis. In contrast, acidosis attenuated the effects on the time course of inactivation and the degree of tonic- and frequency-dependent block for both drugs. CONCLUSION: Extracellular acidosis significantly decreases the potency of blockade of Kv4.3 by both flecainide and quinidine. This change in potency may be due to allosteric changes in the channel, changes in the proportion of uncharged drug, and/or changes in the kinetics of drug binding or unbinding. These findings are in contrast to the effects of extracellular acidosis on block of the fast sodium channel by these agents and provide a molecular mechanism for divergent modulation of drug block potentially leading to ischemia-associated proarrhythmia.     

Characterisation of Kv4.3 in HEK293 cells: comparison with the rat ventricular transient outward potassium current.

OBJECTIVE: The Shal (or Kv4) gene family has been proposed to be responsible for primary subunits of the transient outward potassium current (Ito). More precisely, Kv4.2 and Kv4.3 have been suggested to be the most likely molecular correlates for Ito in rat cells. The purpose of the present study was to compare the properties of the rat Kv4.3 gene product when expressed in a human cell line (HEK293 cells) with that of Ito recorded from rat ventricular cells. METHODS: The cDNA encoding the rat Kv4.3 potassium channel was cloned into the pHook2 mammalian expression vector and expressed into HEK293. Patch clamp experiments using the whole cell configuration were used to characterise the electrophysiological parameters of the current induced by Kv4.3 in comparison with the rat ventricular myocyte Ito current. RESULTS: The transfection of HEK293 cells with rat Kv4.3 resulted in the expression of a time- and voltage-dependent outward potassium current. The current activated for potentials positive to -40 mV and the steady-state inactivation curve had a midpoint of -47.4 +/- 0.3 mV and a slope of 5.9 +/- 0.2 mV. Rat ventricular Ito current was activated at potentials positive to -20 mV and inactivated with a half-inactivation potential and a Boltzmann factor of -29.1 +/- 0.7 mV and 4.5 +/- 0.5 mV, respectively. The time course of recovery from inactivation of rat Kv4.3 expressed in HEK293 cells and of Ito recorded from native rat ventricular cells were exponentials with time constants of 213.2 +/- 4.1 msec and 23. +/- 1.5 msec, respectively. Pharmacologically, Ito of rat myocytes showed a greater sensitivity to 4-aminopyridine than Kv4.3 since half-maximal effects were obtained with 1.54 +/- 0.13 mM and 0.14 +/- 0.02 mM on Kv4.3 and Ito, respectively. In both Kv4.3 and Ito, 4-aminopyridine appears to bind to the closed state of the channel. Finally, although a higher level of expression was observed in the atria compared to the ventricle, the distribution of the Kv4.3 gene across the ventricles appeared to be homogeneous. CONCLUSION: The results of the present study show that Kv4.3 channel may play a major role in the molecular structure of the rat cardiac Ito current. Furthermore, because the distribution of Kv4.3 across the ventricle is homogeneous, the blockade of this channel by specific drugs may not alter the normal heterogeneity of Ito current.     

An essential role for cortactin in the modulation of the potassium channel Kv1.2

Ion channels are key determinants of membrane excitability. The actin cytoskeleton has a central role in morphology, migration, intracellular transport, and signaling. In this article, we show that the actin-binding protein cortactin regulates the potassium channel Kv1.2 and thereby provides a direct link between actin dynamics and membrane excitability. In previous reports, we showed that the tyrosine phosphorylation-mediated suppression of Kv1.2 ionic current occurs by endocytosis of the channel protein. Pull-down assays using recombinant-purified cortactin and Kv1.2 demonstrated that their interaction is direct and reduced by tyrosine phosphorylation of Kv1.2. This finding suggests a link between cortactin and Kv1.2 endocytosis. Here, we confirm that relationship and identify the molecular mechanisms involved. We use FRET to demonstrate that Kv1.2 and cortactin interact in vivo. By manipulating the cortactin-binding site within Kv1.2, we confirm that cortactin proximity influences channel function. We used flow cytometry in conjunction with cortactin gene replacement to identify C-terminal tyrosines, the fourth repeat actin-binding domain, and the N-terminal Arp2/3-binding region, as critical to Kv1.2 regulation. Surprisingly, cortactin's dynamin-binding Src homology 3 domain is not required for Kv1.2 endocytosis, despite that process being dynamin-dependent. These findings predict that cortactin-mediated actin remodeling in excitable cells is not only important for cell structure, but may directly impact membrane excitability.     

Blockers of the Kv1.5 channel for the treatment of atrial arrhythmias

Atrial arrhythmias are a common problem in cardiological practice. Despite the availability of several antiarrhythmic drugs, there is a medical need for safer and more efficient antiarrhythmic treatment. Compounds that act atrial selectively without prolonging the QTc-time and without negative inotropy to terminate and/or prevent atrial arrhythmias would be of high interest. In this context, the voltage-gated potassium channel Kv1.5 is regarded as a promising target to achieve atrial selectivity, which in turn would be associated with fewer side effects than classical antiarrhythmics. This review summarizes patents and other publications on compounds which show this novel mode of action. The chemistry, selectivity and structure-activity data disclosed in the literature are discussed in light of recent work demonstrating the antiarrhythmic efficacy of Kv1.5 blockers in vivo. Several studies in pig, dog or goat models have confirmed their proposed atrial selective antiarrhythmic effect in vivo. Most of the more intensively characterized Kv1.5 blockers have turned out not to be selective but also block other ion channels. Based on the currently available data it seems that additional inhibition of Kv4.3 and KACh is beneficial for the desired antiarrhythmic effect or at least does not hamper the atrial selectivity of a Kv1.5 blocker. Significant block of IK1, HERG or sodium channels, however, clearly leads to loss of atrial selectivity and increases the risk of lethal ventricular proarrhythmia.     

阿魏酸钠与胺碘酮对家兔心室肌电生理作用的频率依赖性影响

与典型的Ⅲ类抗心律失常药物胺碘酮对比 ,研究在整体条件下阿魏酸钠对家兔心室肌电生理特性频率依赖性的影响。 16只家兔随机分为阿魏酸钠组与胺碘酮组 ,应用单相动作电位 (MAP)技术和心脏电刺激方法测定电生理参数 ,比较用药前后、窦性心律及不同起搏频率下心室肌有效不应期 (ERP)、MAP复极 90 %时程 (MAPD90 )的变化。胺碘酮用药后 15min ,在窦律及 180 ,2 0 0 ,2 2 0次 /分起搏频率下 ,MAPD90 的变化率分别为 5 1.5 2± 13.99,5 2 .35±14.5 0 ,5 6 .19± 14.6 3,5 7.15± 16 .6 6 (% ) ,ERP的变化率分别为 5 6 .34± 15 .6 6 ,6 0 .32± 17.0 1,6 1.2 4± 15 .5 4,6 1.0 2±14.0 3(% ) ;阿魏酸钠用药后 2 5min ,在窦律及 2 5 0 ,2 70 ,2 90次 /分起搏频率下 ,MAPD90 的变化率分别为 18.5 3± 3.78,15 .71± 4.41,18.0 0± 6 .12 ,2 0 .48± 5 .6 2 (% ) ,ERP的变化率分别为 18.2 5± 4.6 7,19.76± 3.6 4,2 1.31± 4.18,19.2 5±4.38(% )。结果表明 :阿魏酸钠与胺碘酮作用相似 ,用药后不同起搏频率与窦律时的ERP、MAPD90 变化率及ERP/MAPD90 比值的变化差异无显著性 ,P >0 .0 5。结论 :在整体条件下 ,阿魏酸钠延长心肌复极无逆频率依赖性     

替米沙坦对电压依赖性的Kv1.3和Kv1.5通道电流阻断作用的实验研究

目的 通过观察替米沙坦对电压依赖性的Kv1.3和Kv1.5的阻断作用,探讨替米沙坦对此类通道的阻断可能具有的临床作用.方法 使用双电极电压钳技术记录表达于非洲爪蟾卵母细胞的Kv1.3和Kv1.5钾通道电流,不同浓度灌流观察其对电流影响.结果 (1)替米沙坦浓度依赖性的阻断Kv1.3通道,其阻断的IC50是2.05 μmol/L.替米沙坦对Kv1.3电流的阻断具有电压依赖性.(2)替米沙坦浓度依赖件的阻断Kv1.5通道,其阻断的IC50是2.37 μmol/L.替米沙坦对Kv1.5电流的阻断具有更显著的电压依赖性.结论 替米沙坦阻断开放状态的Kv1.3可能是其发挥免疫调节和抗动脉粥样硬化作用的机制之一.替米沙坦对开放状态的Kv1.5钾通道的阻断可能是其减少心房颤动发生率的作用机制之一.