丹酚酸B对大鼠心室肌细胞瞬时外向钾电流和L型钙电流的阻滞作用

目的研究从丹参中分离提取的药物单体——丹酚酸B对大鼠心肌细胞上的瞬时外向钾电流(Ito)、内向整流钾电流(IK1)和L型钙电流(ICa,L)的电生理学作用。方法用酶解法分离大鼠心室肌细胞,全细胞膜片钳技术记录Ito、IK1和ICa,L。每个细胞采用加药前后自身对照,用含100μmol/L丹酚酸B的细胞外液灌流心室肌细胞,记录加药前、后的电流,所有数据均在细胞破膜后20min内完成。结果 100μmol/L的丹酚酸B对Ito和ICa,L具有抑制作用,使Ito和ICa,L最大激活峰值电流密度下降,电流密度-电压曲线下移;且丹酚酸B主要抑制Ito的快速电流成分Itof,而对Ito的缓慢电流成分Itos无明显作用。在60mV测试电压下,Itof的最大激活峰值电流密度从23.51±3.29pA/pF降为16.85±2.36pA/pF,抑制率为28.31%±10.6%(n=8,P0.05)。在-10mV测试电压下,100μmol/L丹酚酸B作用后ICa,L的最大激活峰值电流密度从-8.66±-2.40pA/pF降为-5.91±-2.14pA/pF,抑制率为31.84%±10.23%(n=11,P0.05)。丹酚酸B使Ito通道失活后的恢复减慢,但不改变ICa,L的通道动力学。丹酚酸B对IK1无显著作用。结论丹酚酸B对Ito和ICa,L具有阻滞作用,而对IK1无显著作用。     

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.     

血管紧张素Ⅱ对人心房肌细胞膜钾钙离子电流的作用

观察血管紧张素Ⅱ对人心房肌细胞膜主要离子流的作用,揭示其参与房性心律失常的细胞电生理机制。急性分离单个人心房肌细胞,采用全细胞膜片钳方法记录细胞膜短暂外向钾电流(Ito)、内向整流钾电流(Ik1)和L型钙电流(ICaL)。结果:0.1μmol/LAngⅡ使人心房肌细胞膜Ito峰值电流密度明显下降6.54±0.49pA/pFvs12.65±0.86pA/pF(P<0.05),在-100mV电压下使IK1峰值电流密度显著升高-8.93±1.12pA/pFvs-5.23±0.95pA/pF,(P<0.05),并明显促进人心房肌细胞膜ICaL-12.72±1.69pA/pFvs-5.79±0.84pA/pF(P<0.05)。结论:AngⅡ可促进人心房肌细胞膜IK1及ICaL,抑制人心房肌细胞膜Ito。     

缬沙坦对血管紧张素Ⅱ引起人心房肌细胞离子电流改变的调节作用

目的:研究缬沙坦对血管紧张素Ⅱ(AngⅡ)引起人心房肌细胞离子电流改变的调节作用。方法:经典两步酶解法分离单个心房肌细胞,膜片钳全细胞法记录离子电流。结果:AngⅡ(300nmol/L)使快速内向钠电流(INa)从(-15.83±1.62)电流(pA)/电容(pF)降到(-6.35±1.83)pA/pF(P<0.01),其作用不能被缬沙坦(10μmol/L)抑制;使L型钙电流(ICa-L)从(-4.5±1.64)pA/pF增加到(-5.5±1.95)pA/pF(P<0.05),其作用能被缬沙坦抑制;指令电位-120mV时使内向整流性钾电流(IK1)从(-3.49±1.03)pA/pF增加到(-5.47±1.83)pA/pF(P<0.01),+10mV~+50mV时其外向电流成分随电压而增加,其作用不能被缬沙坦抑制。AngⅡ对超速激活延迟整流性钾电流(IKur)和瞬间外向钾电流(Ito1)无显著影响。结论:AngⅡ对人心房肌细胞ICaL有促进作用并可被缬沙坦抑制;增加IK1,抑制INa,其作用不能被缬沙坦抑制。     

盐酸关附甲素对豚鼠和大鼠心肌细胞钾通道的阻断作用

目的用膜片钳全细胞记录法观察盐酸关附甲素(GFA)对分离的单个豚鼠心室肌细胞缓慢激活型延迟整流钾电流(IKs),大鼠内向整流钾电流(IK1)、瞬时外向钾电流(Ito)的影响。方法用急性酶解法分离获得单个豚鼠和大鼠心室肌细胞。用标准的全细胞膜片钳技术记录IKs、IK1、Ito离子通道电流,观察不同浓度的GFA对豚鼠心室肌细胞IKs,大鼠心室肌细胞IK1、Ito的影响。结果50,150,500μmol/LGFA使IKs尾电流(IKs,tail)最大峰值电流密度分别降低11.4%±3.32%、23.3%±7.36%、36.7%±4.99%,P<0.05;使IK1稳态电流密度分别降低5.1%±0.6%、7.5%±0.9%、7.2%±0.9%;50,500μmol/LGFA使Ito最大峰值电流密度分别降低6.1%±0.64%、8.6%±1.13%。结论GFA对IKs具有浓度依赖性阻滞作用,这可能是其延长动作电位时程而对静息电位影响不大的电生理基础,是其抗心律失常作用的机制之一。     

胺碘酮对模拟缺氧状态下大鼠心室肌细胞瞬时外向和内向整流钾电流的影响

目的通过观察胺碘酮对模拟缺氧状态下急性分离的大鼠心室肌单细胞复极相中瞬时外向钾电流(Ito)和内向整流钾电流(IK1)通道的影响,探讨其在该条件下抗心律失常的作用机制。方法使用酶解法分离获取大鼠单个心室肌细胞,通过持续通以模拟缺氧细胞外液建立体外模拟缺氧模型,采用全细胞膜片钳实验技术研究胺碘酮对该条件下Ito和IK1的作用。结果胺碘酮呈剂量依赖性降低Ito和IK1电流幅值,对Ito抑制效应的起始浓度为1μmol/L,100μmol/L时抑制作用达最大,最大抑制幅度为56.78%±4.27%(23.98±2.18pA/pFvs10.38±4.27pA/pF;测试电压为+70mV;P<0.01;n=5),IC50(半数抑制浓度)为74.35μmol/L,但Ito的I-V曲线趋势并没有发生变化,稳态激活和失活曲线几乎不发生移动。胺碘酮对IK1内向电流部分抑制起始浓度为1μmol/L,外向电流部分抑制效应的起始浓度为2μmol/L,其最大抑制幅度分别为58.77%±10.76%(56.32±7.24pA/pFvs23.22±7.30pA/pF;测试电压为-150mV;P<0.01)和33.29%±2.15%(6.70±0.89pA/pFvs4.46±0.93pA/pF;测试电压为+40mV;P<0.01;n=5)。对内向电流成分的IC50为63.75μmol/L,IK1通道的稳态激活曲线无明显改变。结论在大鼠离体心室肌单细胞模拟缺氧条件下,胺碘酮对Ito和IK1电流幅度呈剂量依赖性抑制,有对抗缺氧本身造成的动作电位时程缩短效应;对I内向电流成分的敏感性高于外向成分。     

钾通道与心血管临床

一、心肌K+ 通道有以下几类1.外向整流通道 (Kv)由膜去极化激活 ,产生外向钾电流 ,负责心肌动作电位的各期复极化。在快反应细胞如心室肌中 ,复极 1期是由短暂外向钾电流 (Ito)所产生 ;内向性钙电流 (ICa)和外向性钾电流(IK)的相互平衡是形成 2期平台的主要因素 ;钙电流的失活和IK 的缓慢成分 (IKs)的继续 ,使外向电流超过内向电流而触发 3期快速复极化 ,3期复极化主要为外向钾电流的快速成分 (IKr)所产生。IKr又称钾外向背景电流 (IK1 )。IKs,IKr在细胞外钾浓度增高时增强 ,故称整流通道。2 .内向整流通过 (KIR,IK)保持心脏舒张…     

1-磷酸鞘氨醇对心肌细胞延迟整流钾电流2种成分的作用

目的:研究1-磷酸鞘氨醇(S1P)对豚鼠心室肌细胞延迟整流钾电流的2种成分快速激活整流钾电流(IKr)和缓慢激活整流钾电流(IKs)的作用。方法:用胶原酶酶解法急性分离豚鼠心室肌细胞,随机分为正常对照组、S1P(1.1μmol/L)组、S1P(1.1μmol/L)加苏拉明(Suramin)(200μmol/L)组。利用全细胞膜片钳的方法记录心室肌细胞IKr和IKs及其尾电流。结果:①对照组IKr和IKr的尾电流分别为(0.85±0.53)nA和(0.65±0.40)nA。加入S1P后,IKr和IKr的尾电流受到明显抑制,下降到(0.63±0.37)nA和(0.56±0.29)nA(P<0.05,n=6)。而加入S1P加Suramin后,抑制作用消失,IKr和IKr的尾电流为(0.85±0.41)nA和(0.71±0.43)nA,与对照组相比差异无统计学意义(P>0.05,n=6)。②对照组IKs和IKs的尾电流分别为(1.53±0.61)nA和(0.82±0.34)nA。加入S1P后,下降到(1.47±0.46)nA和(0.79±0.41)nA,但差异无统计学意义(P>0.05,n=6)。结论:S1P可降低豚鼠心室肌细胞IKr的幅值,并且是通过其特异性的G蛋白耦联S1P受体介导而产生这些作用。S1P对豚鼠心室肌细胞IKs没有作用。     

BmkTXK β对家兔心房肌细胞钾电流的影响

为研究东亚钳蝎毒素BmkTXKβ对家兔心房肌单细胞电生理特征的影响 ,应用全细胞膜片钳技术记录各项钾电流和动作电位。结果 :BmkTXKβ呈浓度依赖性地延长动作电位时程 (APD2 0 、APD50 和APD90 ) ,但对动作电位幅度 (APA) ,静息膜电位 (RMP)和 0相最大除极速度 (Vmax)无明显影响 (n =9)。在刺激电压 +5 0mV时 1μmol/L的BmkTXKβ使心房肌细胞瞬间外向钾电流 (Ito)从 13.6 3± 0 .87pA/pF减少到 7.98± 0 .78pA/pF ,抑制率为 41.4%(n=10 ,P <0 .0 1)。同时 ,这种作用具有显著的浓度依赖性 ,抑制 5 0 %的电流所需浓度 (IC50 )的均值为 0 .95 μmol/L。BmkTXKβ可抑制延迟整流性钾电流 (IK) ,表现为剂量依赖性阻断的形式。 10 μmol/L时 (刺激电压 +70mV) ,它对IK的抑制率为 39.3 %(从 5 .86± 0 .6 4pA/pF降到 3 .5 6± 0 .5 8pA/pF ,n =6 ,P <0 .0 5 )。IC50 的均值为 2 .76 μmol/L。但BmkTXKβ对内向整流钾电流 (IK1)的电流幅值及其反转电位基本无影响 (n =6 ,P >0 .0 5 )。结论 :BmkTXKβ阻断Ito和IK 等与心脏复极相关的钾离子通道 ,且能在多个环节显著延长APD。     

钾通道与心血管临床

1．外向整流通道(Kv)由膜去极化激活，产生外向钾电流，负责心肌动作电位的各期复极化。在快反应细胞如心室肌中，复极1期是由短暂外向钾电流(Ito)所产生；内向性钙电流(ICa)和外向性钾电流(IK)的相互平衡是形成2期平台的主要因素；钙电流的失活和，K的缓慢成分(IK2)的继续，使外向电流超过内向电流而触发3期快速复极化，3期复极化主要为外向钾电流的快速成分(IKr)所产生。IKr又称钾外向背景电流(IK1)。IKs，IKr在细胞外钾浓度增高时增强，故称整流通道。     

Delayed rectifier potassium current in undiseased human ventricular myocytes

OBJECTIVE: The purpose of the study was to investigate the properties of the delayed rectifier potassium current (IK) in myocytes isolated from undiseased human left ventricles. METHODS: The whole-cell configuration of the patch-clamp technique was applied in 28 left ventricular myocytes from 13 hearts at 35 degrees C. RESULTS: An E-4031 sensitive tail current identified the rapid component of IK (IKr) in the myocytes, but there was no evidence for an E-4031 insensitive slow component of IK (IKs). When nifedipine (5 microM) was used to block the inward calcium current (ICa), IKr activation was fast (tau = 31.0 +/- 7.4 ms, at +30 mV, n = 5) and deactivation kinetics were biexponential and relatively slow (tau 1 = 600.0 +/- 53.9 ms and tau 2 = 6792.2 +/- 875.7 ms, at -40 mV, n = 7). Application of CdCl2 (250 microM) to block ICa altered the voltage dependence of the IKr considerably, slowing its activation (tau = 657.1 +/- 109.1 ms, at +30 mV, n = 5) and accelerating its deactivation (tau = 104.0 +/- 18.5 ms, at -40 mV, n = 8). CONCLUSIONS: In undiseased human ventricle at 35 degrees C IKr exists having fast activation and slow deactivation kinetics; however, there was no evidence found for an expressed IKs. IKr probably plays an important role in the frequency dependent modulation of repolarization in undiseased human ventricle, and is a target for many Class III antiarrhythmic drugs.     

Heterogeneous distribution of the two components of delayed rectifier K+ current: a potential mechanism of the proarrhythmic effects of methanesulfonanilideclass III agents.

OBJECTIVE: To elucidate the regional difference of the K+ current blocking effects of methanesulfonanilide class III agents. METHODS: Regional differences in action potential duration (APD) and E-4031-sensitive component (IKr) as well as -insensitive component (IKs) of the delayed rectifier K+ current (IK) were investigated in enzymatically isolated myocytes from apical and basal regions of the rabbit left ventricle using the whole-cell clamp technique. RESULTS: At 1 Hz stimulation, APD was significantly longer in the apex than in the base (223.1 +/- 10.6 vs. 182.7 +/- 14.5 ms, p < 0.05); application of 1 microM E-4031 caused more significant APD prolongation in the apex than in the base (32.5 +/- 6.4% vs. 21.0 +/- 8.8%, p < 0.05), resulting in an augmentation of regional dispersion of APD. In response to a 3-s depolarization pulse to +40 mV from a holding potential of -50 mV, both IK tail and IKs tail densities were significantly smaller in apical than in basal myocytes (IK: 1.56 +/- 0.13 vs. 2.09 +/- 0.21 pA/pF, p < 0.05; IKs: 0.40 +/- 0.15 vs. 1.43 +/- 0.23, p < 0.01), whereas IKr tail density was significantly greater in the apex than in the base (1.15 +/- 0.13 vs. 0.66 +/- 0.11 pA/pF, p < 0.01). The ratio of IKs/IKr for the tail current in the apex was significantly smaller than that in the base (0.51 +/- 0.21 vs. 3.09 +/- 0.89; p < 0.05). No statistical difference was observed in the voltage dependence as well as activation and deactivation kinetics of IKr and IKs between the apex and base. Isoproterenol (1 microM) increased the time-dependent outward current of IKs by 111 +/- 8% during the 3-s depolarizing step at +40 mV and its tail current by 120 +/- 9% on repolarization to the holding potential of -50 mV, whereas it did not affect IKr. CONCLUSIONS: The regional differences in IK, in particular differences in its two components may underlie the regional disparity in APD, and that methanesulfonanilide class III antiarrhythmic agents such as E-4031 may cause a greater spatial inhomogeneity of ventricular repolarization, leading to re-entrant arrhythmias.     

兔界嵴细胞离子通道特性研究

目的研究生理状态下及异丙肾上腺素灌流对兔界嵴(CT)与梳状肌(PM)细胞动作电位(AP)及钠电流(INa)、短暂外向钾电流(Ito)、L型钙电流(ICa-L)、延迟整流钾电流(IK)及内向整流性钾电流(IK1)的影响,探讨CT与房性心律失常的关系。方法酶解法分离兔CT及PM细胞,利用全细胞膜片钳技术,记录生理状态下及异丙肾上腺素灌流后CT与PM细胞AP及INa、Ito、ICa-L、IK及IK1的变化。结果①生理状态下,CT细胞动作电位时程(APD)较长,可见明显的平台期;PM细胞AP形态与普通心房肌细胞相似,1期复极迅速,平台期短,类似三角形。②生理状态下,CT细胞Ito电流密度比PM细胞明显降低(7.13±0.38 pA/pF vs 10.70±0.62 pA/pF,n=9,P<0.01),而INa、Ito、ICa-L、IK及IK1则无明显差别。③异丙肾上腺素灌流时CT与PM细胞APD20、APD50、APD90均延长(n=8,P<0.01);指令电位+50 mV时,CT与PM细胞Ito电流密度均减少(n=9,P<0.01)而IK均增加(n=8,P<0.05);指令电位+10 mV时,CT与PM细胞ICa-L电流密度均增加(n=9,P<0.01);IK1在两种心肌细胞均无明显差异。结论 CT与PM细胞AP差异与Ito有关。异丙肾上腺素灌流时ICa-L与IK增强,Ito抑制使CT与PM细胞APD延长,触发机制可能是CT参与房性心律失常的机制之一。     

Isoproterenol antagonizes prolongation of refractory period by the class III antiarrhythmic agent E-4031 in guinea pig myocytes. Mechanism of action

The mechanism by which isoproterenol (ISO) prevents the prolongation of action potential duration (APD) and refractory period (RP) by the class III antiarrhythmic agent E-4031 was studied. E-4031 (1 microM) increased RP by 50% with no effect on contractile force in papillary muscles isolated from guinea pig heart. ISO (1 microM) increased force of contraction more than fivefold and decreased RP by 25%. The prolongation of RP by E-4031 was prevented by pretreatment of muscles with ISO. The prolongation of APD in isolated guinea pig ventricular myocytes by 5 microM E-4031 also was antagonized by prior exposure of the cells to 1 microM ISO. Instantaneous currents and delayed rectifier K+ currents, IK, were measured in isolated myocytes using the suction microelectrode voltage-clamp technique. Currents were measured in response to 225-msec depolarizing pulses from a holding potential of -40 mV. Previous studies have demonstrated that IK in these cells results from activation of two distinct outward K+ currents, IKs and IKr (specifically blocked by E-4031). ISO doubled the magnitude of IKs without significant effect on IKr. The instantaneous current, putatively identified as a Cl- current, also was doubled by ISO but was unaffected by E-4031. The augmented conductance of IKs and instantaneous current by ISO results in a decrease in RP. The small effect of E-4031 on APD and RP in the presence of ISO results from the smaller contribution of IKr relative to the augmented repolarizing currents.     

Pharmacology of cardiac potassium channels

Cardiac K+ channels are membrane-spanning proteins that allow the passive movement of K+ ions across the cell membrane along its electrochemical gradient. They regulate the resting membrane potential, the frequency of pacemaker cells and the shape and duration of the cardiac action potential. Additionally, they have been recognized as potential targets for the actions of neurotransmitters and hormones and class III antiarrhythmic drugs that prolong the action potential duration (APD) and refractoriness and have been found effective to prevent/suppress cardiac arrhythmias. In the human heart, K+ channels include voltage-gated channels, such as the rapidly activating and inactivating transient outward current (Ito1), the ultrarapid (IKur), rapid (IKr) and slow (IKs) components of the delayed rectifier current and the inward rectifier current (IK1), the ligand-gated channels, including the adenosine triphosphate-sensitive (IKATP) and the acetylcholine-activated (IKAch) currents and the leak channels. Changes in the expression of K+ channels explain the regional variations in the morphology and duration of the cardiac action potential among different cardiac regions and are influenced by heart rate, intracellular signalling pathways, drugs and cardiovascular disorders. A progressive number of cardiac and noncardiac drugs block cardiac K+ channels and can cause a marked prolongation of the action potential duration (i.e. an acquired long QT syndrome, LQTS) and a distinct polymorphic ventricular tachycardia termed torsades de pointes. In addition, mutations in the genes encoding IKr (KCNH2/KCNE2) and IKs (KCNQ1/KCNE1) channels have been identified in some types of the congenital long QT syndrome. This review concentrates on the function, molecular determinants, regulation and, particularly, on the mechanism of action of drugs modulating the K+ channels present in the sarcolemma of human cardiac myocytes that contribute to the different phases of the cardiac action potential under physiological and pathological conditions.     

慢性压力超负荷左室电重构的异质性及离子基础

目的研究慢性压力超负荷左室电重构的异质性及离子基础。方法新西兰兔通过肾上腹主动脉次全结扎诱发左室慢性压力超负荷。采用全细胞膜片钳技术分别记录对照组及手术组左室内膜、中层及外膜细胞的动作电位,慢激活的延迟整流钾电流(IKs)及快激活的延迟整流钾电流(IKr)等。结果与对照组比较,基础周长为2s时,手术组左室内膜、中层及外膜细胞的动作电位复极90%的时程(APD90)分别延长27.7%、27.2%(P<0.05或0.01)、19.6%(P>0.05);对照组中层细胞的APD90较外膜细胞长50.8%,而手术组为60.4%;在测试电位为+50mV时,手术组左室内膜、中层及外膜细胞IKs尾电流密度分别减小26.1%、36.3%(P均<0.05)、23.0%(P>0.05);IKr尾电流密度分别减小31.7%、30.5%、30.0%(P<0.01或0.05)。对照组外膜细胞的IKs尾电流密度较中层细胞大49.1%,而手术组为77.6%;两组三层细胞之间IKr尾电流密度均无差别。结论正常兔左室存在跨壁复极异质性,心肌肥厚时进一步扩大,IKs分布及下调的不均一性是其离子流基础。     

Comparison of the in vivo electrophysiological and proarrhythmic effects of amiodarone with those of a selective class III drug, sematilide, using a canine chronic atrioventricular block model.

Amiodarone effectively blocks both the sodium and calcium channels and beta-adrenoceptors, in addition to blocking several potassium currents including IKr, IKs, Ito, IK1, IKACh and IKNa. The incidence of clinical torsade de pointes (TdP) associated with amiodarone has been reported to be low and the present study compared the proarrhythmic potential of amiodarone with that of a selective IKr channel blocker, sematilide, using a canine chronic atrioventrucular block model. Amiodarone or sematilide (3 and 30 mg/kg; n=4 for each group) was administered orally without anesthesia under continuous ECG monitoring. Both drugs prolonged the QT interval, although the onset was faster for sematilide. The high dose of sematilide induced TdP in 3 of 4 animals, which caused their death, but neither the low dose of sematilide nor the 2 dosages of amiodarone induced lethal ventricular arrhythmias. These results suggest that IKr channel inhibition by amiodarone with its additional ion channel blocking action may contribute to the prevention of TdP.     

Repolarizing K+ currents ITO1 and IKs are larger in right than left canine ventricular midmyocardium

BACKGROUND: The ventricular action potential exhibits regional heterogeneity in configuration and duration (APD). Across the left ventricular (LV) free wall, this is explained by differences in repolarizing K+ currents. However, the ionic basis of electrical nonuniformity in the right ventricle (RV) versus the LV is poorly investigated. We examined transient outward (ITO1), delayed (IKs and IKr), and inward rectifier K+ currents (IK1) in relation to action potential characteristics of RV and LV midmyocardial (M) cells of the same adult canine hearts. METHODS AND RESULTS: Single RV and LV M cells were used for microelectrode recordings and whole-cell voltage clamping. Action potentials showed deeper notches, shorter APDs at 50% and 95% of repolarization, and less prolongation on slowing of the pacing rate in RV than LV. ITO1 density was significantly larger in RV than LV, whereas steady-state inactivation and rate of recovery were similar. IKs tail currents, measured at -25 mV and insensitive to almokalant (2 micromol/L), were considerably larger in RV than LV. IKr, measured as almokalant-sensitive tail currents at -50 mV, and IK1 were not different in the 2 ventricles. CONCLUSIONS: Differences in K+ currents may well explain the interventricular heterogeneity of action potentials in M layers of the canine heart. These results contribute to a further phenotyping of the ventricular action potential under physiological conditions.     

Effects of sea anemone toxin anthopleurin-Q on potassium currents in rats and guinea pig ventricular myocytes

To investigate the effect of sea anemone toxin anthopleurin-Q (AP-Q) on potassium currents in isolated rats and guinea pig ventricular myocytes.Methods The ventricular cells of guinea pigs and SD rats were obtained by enzymatic dissociation method.Whole cell patch clamp technique was used to record potassium currents (Ito,IK,and IK1).Results AP-Q 3-100 nmol/L increased Ito in a concentration-dependent manner,with an EC50 value of 12.7 nmol/L.At a potential of +50mV,AP-Q 10nmol/L increased Ito from (13.3±3.4) pA pF-1 to (19.46±4.3) pA pF-1.AP-Q 0.1-100 nmol/L increased IK and IK tail in a concentration-dependent manner with EC50 values of 4.7 nmol/L and 5.0 nmol/L,respectively.AP-Q 1 pmol/L-100 nmol/L increased IK1 in dose-dependent manner,with an EC50 of 0.2 nmol/L.Conclusions The effect of AP-Q on Ito,IK and IK1 may partly explain its mechanism in shortening APD and increasing RP.(J Geriatr Cardiol 2008;5:243-247)     

Ionic targets for drug therapy and atrial fibrillation-induced electrical remodeling: insights from a mathematical model.

Recent advances in molecular electrophysiology have made possible the development of more selective ion channel blockers for therapeutic use. However, more information is needed about the effects of blocking specific channels on repolarization in normal human atrium and in atrial cells of patients with atrial fibrillation (AF). AF-induced electrical remodeling is associated with reductions in transient outward current (Ito), ultrarapid delayed rectifier current (IKur), and L-type calcium current (ICa,L). Direct evaluation of the results of ion channel depression is limited by the nonspecificity of the available pharmacological probes. OBJECTIVES: Using a mathematical model of the human atrial action potential (AP), we aimed to: (1) evaluate the role of ionic abnormalities in producing AP changes characteristic of AF in humans and (2) explore the effects of specific channel blockade on the normal and AF-modified AP (AFAP). METHODS: We used our previously developed mathematical model of the normal human atrial AP (NAP) based on directly measured currents. We constructed a model of the AFAP by incorporating experimentally-measured reductions in Ito (50%), IKur (50%), and ICa,L (70%) current densities observed in AF. RESULTS: The AFAP exhibits the reductions in AP duration (APD) and rate-adaption typical of AF. The reduction in ICa,L alone can account for most of the morphological features of the AFAP. Inhibition of Ito by 90% leads to a reduction in APD measured at -60 mV in both the NAP and AFAP. Inhibition of the rapid component of the delayed rectifier (IKr) by 90% slows terminal repolarization of the NAP and AFAP and increases APD by 38% and 34%, respectively. Inhibition of IKur by 90% slows early repolarization and increases plateau height, activating additional IK and causing no net change in APD at 1 Hz in the NAP. In the presence of AF-induced ionic modifications, IKur inhibition increases APD by 12%. Combining IKur and IKr inhibition under both normal and AF conditions synergistically increases APD. In the NAP, altering the model parameters to reproduce other typical measured AP morphologies can significantly alter the response to K(+)-channel inhibition. CONCLUSIONS: (1) The described abnormalities in Ito, IKur and ICa,L in AF patients can account for the effects of AF on human AP properties; (2) AP prolongation by IKur block is limited by increases in plateau height that activate more IK; (3) Blockers of IKur may be more effective in prolonging APD in patients with AF; 4) Inhibition of both IKur and IKr produces supra-additive effects on APD. These observations illustrate the importance of secondary current alterations in the response of the AP to single channel blockade, and have potentially important implications for the development of improved antiarrhythmic drug therapy for AF.