压力超负荷对大鼠左室心肌牵张敏感性钾通道TREK-1 mRNA和蛋白表达的影响

目的探讨压力超负荷状态下左室心肌牵张敏感性钾通道TREK-1mRNA及其蛋白表达的变化。方法雄性W istar大鼠被随机分为腹主动脉缩窄组(n=30)和假手术组。腹主动脉缩窄组依观察时间随机分为2,4,8周组各10只。每组观察期结束后,计算左右室肥厚指数(LVM I、RVM I)。HE染色观察压力超负荷对心肌组织结构的影响。采用RT-PCR和免疫组织化学SABC法分别检测牵张敏感性钾通道TREK-1mRNA与蛋白水平表达的改变。结果腹主动脉缩窄术后2周,出现左室肥厚,但无统计学意义。腹主动脉缩窄术后4,8周,左室肥厚指数较正常组明显增加(P<0.05),光镜下显示心肌肥厚。术后2,4,8周组左室心肌牵张敏感性钾通道TREK-1mRNA上调(P<0.05),心肌细胞内TREK-1蛋白表达明显增加(P<0.05)。结论压力超负荷致大鼠左室肥厚的同时可诱导牵张敏感性钾通道TREK-1的表达增加。     

辛伐他汀对大鼠心肌肥厚的防治作用及其与钙通道的关系

目的 探讨辛伐他汀对心肌肥厚的防治作用及其与钙通道活动的关系.方法 采用腹主动脉缩窄术建立心肌肥厚动物模型.尾动脉无创测量大鼠收缩压.称量心脏重量/体重(HW/BW)、左心室重量/体重(LVW/BW)比值.采用超声心动图检测动物心脏构型及射血功能.应用RT-PCR和Western blot分别检测心肌L-型钙通道亚单位Cav1.2(α,C)、T-型钙通道亚单位Cav3.1 (α1G)、Cav3.2(α1H)mRNA及其蛋白表达的变化.结果 (1)腹主动脉缩窄+辛伐他汀组(AAC+SIM组)大鼠收缩压130 mm Hg(1 mm Hg=0.133 kPa)明显低于腹主动脉缩窄组(AAC组)189mm Hg,P<0.05.HW/BW比值AAC+SIM组3.37 mg/g明显低于AAC组3.94 mg/g,P<0.01.LVW/BW比值AAC+SIM组2.33 mg/g明显低于AAC组2.95 mg/g,P<0.01.室间隔厚度AAC+SIM组2.01 mm明显低于AAC组2.31 mm,P<0.01.左心室后壁厚度AAC+SIM组1.89 mm明显低于AAC组2.19 mm,P<0.01.(2)AAC+SIM组大鼠心肌T-型钙通道亚单位α1G、α1H mRNA和蛋白表达均显著低于AAC组,P均<0.01,但L-型钙通道亚单位α1 C mRNA和蛋白表达两组间比较差异无统计学意义.结论 辛伐他汀对腹主动脉缩窄所致的心肌肥厚具有明显的防治作用,其作用机制可能与其抑制T-型钙通道亚单位α1G、α1H mRNA和蛋白的重新再表达有关,但与L-型钙通道亚单位α1C mRNA和蛋白表达无关.     

钾离子通道亚单位mRNA在犬左右心室中层心肌中的表达

目的研究犬左右室中层心肌短暂外向钾电流(Ito)、延迟整流钾电流缓慢激活成分(Iks)亚单位mRNA的表达情况,探讨左右室复极异质性的可能分子机制。方法应用逆转录-聚合酶链反应(RT-PCR)半定量分析犬左右室中层心肌Ito的α亚单位(Kv4.3)、β亚单位(KchIP2)、Iks的α亚单位(KvLQT1)mRNA的表达量(以β-actin为内参照)。结果Kv4.3 mRNA水平在左右室中层心肌中表达没有显著性差异(P>0.05),KchIP2 mRNA、Kv-LQT1 mRNA水平在右室中层心肌表达明显高于左室中层心肌(P<0.01或<0.05)。结论KchIP2、KvLQT1 mRNA水平在左右室中层心肌中表达上的差异可能是其离子流差异的分子基础。     

miR-350在腹主动脉部分缩窄大鼠心肌组织中的表达及意义

目的观察腹主动脉部分缩窄大鼠心肌组织miR-350在心肌肥厚形成过程中的表达变化并探讨其临床意义。方法将20只雄性SD大鼠随机分成正常组5只、假手术组5只和模型组10只,采用腹主动脉部分缩窄术制备大鼠心肌肥厚模型。采用Trizol法提取心肌组织RNA,芯片技术检测miRNA表达。构建过表达miR-350质粒载体,转染大鼠的胚胎心肌细胞H9c2;采用Real-time PCR方法检测心肌细胞中ANP、BNP、β-myosin及α-actin的表达。结果 miR-350在模型组的表达量明显高于对照组;过表达miR-350的细胞中ANP mRNA及BNP mRNA升高(P<0.05或<0.01)。结论在腹主动脉部分缩窄大鼠的心肌组织中miR-350表达升高,且介导心肌细胞肥厚。     

心肌营养素1在压力超负荷致心肌肥大中的作用

目的研究心肌营养素1在腹主动脉缩窄所致大鼠压力负荷性心肌肥大模型中的作用,观察AG490对心肌肥大及心肌营养素1表达的影响。方法用腹主动脉缩窄的方法建立心肌肥大大鼠模型,检测左心室重量指数,应用逆转录聚合酶链反应检测心肌营养素1、β-肌球蛋白重链mRNA表达,放射免疫分析法测定血浆和心肌血管中血管紧张素Ⅱ水平。结果腹主动脉缩窄术后14天心肌肥大组左心室重量指数明显高于假手术组(P<0.01);AG490干预组左心室重量指数明显低于心肌肥大组(P<0.01),但仍高于假手术组(P<0.01)。心肌肥大组血浆和心肌血管紧张素Ⅱ增高,与假手术组比差异有统计学意义(P<0.01);AG490干预组血管紧张素Ⅱ水平低于心肌肥大组(P<0.05),但仍高于假手术组(P<0.01)。心肌肥大组心肌营养素1mRNA表达较假手术组增加(P<0.01);AG490干预组心肌营养素1表达较心肌肥大组无明显变化(P>0.05),但与假手术组相比表达明显增加(P<0.01)。心肌肥大组心肌β-肌球蛋白重链mRNA表达明显高于假手术组(P<0.01);AG490干预组β-肌球蛋白重链mRNA表达较心肌肥大组明显降低(P<0.01),与假手术组相比表达仍增加(P<0.01)。结论心肌营养素1参与腹主动脉缩窄所致大鼠压力负荷性心肌肥大的发病过程,AG490可抑制心肌营养素1的表达及心肌肥大。     

2型糖尿病大鼠胸主动脉上大电导钙激活钾通道α、β_1亚基蛋白及mRNA的变化

目的探讨不同病程T2DM大鼠胸主动脉上大电导钙激活通道(BKCa)蛋白及mRNA表达的变化。方法 60只大鼠被随机分成对照(Con)组10只和模型(M)组50只。Con组予常规饲养,M组采用高脂高糖饮食且腹腔注射小剂量STZ建立T2DM大鼠模型。免疫印记法和RT-PCR测定胸主动脉BKCa通道α,β1亚单位的蛋白和mRNA表达水平。结果 8周、12周M组BKCaα亚单位蛋白在胸主动脉中的表达为(0.942±0.324)和(0.925±0.521);BKCaɑ亚单位mRNA表达为(0.93±0.03)和(0.92±0.07)。(2)8周、12周M组BKCaβ1亚单位蛋白在胸主动脉中的表达为(0.452±0.25)和(0.401±0.34);BKCaβ1亚单位mRNA表达为(0.56±0.19)和(0.43±0.06)。与Con组比较,8周、12周M组β1亚单位蛋白和mRNA表达降低(P0.05)。结论 T2DM大鼠大血管上BKCa通道β1亚单位蛋白及mRNA的表达在8周及12周降低。     

人心肌细胞缓慢激活延迟整流钾电流细胞模型的建立

目的建立稳定表达人心肌细胞缓慢激活延迟整流钾电流（IKs）的细胞模型。方法编码IKs通道α亚单位的KCNQ1基因及β亚单位的KCNE1基因共转染HEK 293细胞,潮霉素B筛选,电生理学及药理学方法鉴定。结果KCNQ1/KCNE1基因被成功转入HEK 293细胞,KCNQ1/KCNE1电流与人心肌IKs电流具有相似的电流特性;hKCNQ1/hKCNE1通道反转电位与细胞外钾离子浓度呈线性关系;选择性IKs通道阻断剂Chromanol 293B对KCNQ1/KCNE1电流具有明显而可逆的抑制作用,其IC50（+40 mV）为9.1μmol/L;无钾细胞外液可以增加KCNQ1/KCNE1电流幅度,+40 mV时电流幅度增加（28.6±2.0）%（P<0.01,n=8）,但对其动力学特性无明显影响。结论已经成功构建稳定表达人心肌KCNQ1/KCNE1通道蛋白的HEK 293细胞系,其电生理学特性和药理学特性与人心肌IKs相似,可以作为研究人心肌IKs的细胞模型。     

动脉粥样硬化小鼠主动脉平滑肌上瞬时受体电位通道-1-大电导钙离子激活钾通道信号复合体分子表达量的变化研究

目的:观察动脉粥样硬化(AS)小鼠主动脉平滑肌上瞬时受体电位通道-1-大电导钙离子激活钾通道(TRPC1-BK)信号复合体分子表达量的变化。方法:AS组采用载脂蛋白E基因缺陷(ApoE~(-/-))小鼠,对照组采用野生型C57BL/6J小鼠,每组10只,分别采用高脂饲料和普通饲料喂养10周,处死后分离主动脉血管平滑肌组织,提取总核糖核酸(RNA)及总蛋白。使用反转录-聚合酶链式反应(RT-PCR)、蛋白免疫印迹(Western blot)及免疫组化染色等方法检测并比较两组TRPC1、大电导钙离子激活钾通道α亚单位(BKα)及大电导钙离子激活钾通道β_1亚单位(BKβ_1)亚基信使核糖核酸(mRNA)和蛋白表达量的差异。结果:AS组AS模型建立成功。RT-PCR检测结果:与对照组比,AS组TRPC1的mRNA表达量增多(P0.05),BKα和BKβ_1亚基的mRNA表达量减少(P均0.01)。Western blot法检测结果:与对照组比,AS组TRPC1蛋白表达量增多(P0.05),BKα和BKβ_1蛋白表达量减少(P均0.01)。免疫组化染色检测结果:TRPC1蛋白表达量增多(P0.01),BKα蛋白表达量减少(P0.01),BKβ_1蛋白表达量减少(P0.05)。结论:AS组小鼠主动脉平滑肌组织中TRPC1-BK信号复合体的mRNA和蛋白表达量均受影响。推测TRPC1-BK信号复合体有可能成为治疗AS相关性血管疾病的一个新靶点。     

辛二酰苯胺异羟肟酸通过抑制组蛋白去乙酰化酶改善小鼠心肌肥厚的研究

目的:探讨组蛋白去乙酰化酶(HDAC)抑制剂辛二酰苯胺异羟肟酸(SAHA)改善小鼠心肌肥厚的作用,为防治心肌肥厚提供新思路。方法:选取60只昆明小鼠,随机分为正常组、假手术组、心肌肥厚组、心肌肥厚+SAHA组,通过部分结扎小鼠胸主动脉建立心肌肥厚模型,最终每组纳入6只。采用苏木素伊红(HE)染色观察小鼠心肌细胞,超声心动图检测小鼠心功能,比色法检测HDAC活性,小鼠心肌组织中HDAC亚型HDAC5和β-肌球蛋白重链(β-MHC)信使核糖核酸(mRNA)和蛋白表达水平分别运用逆转录-聚合酶链反应(RT-PCR)和蛋白免疫印迹(Western blot)检测。结果:HE染色结果表明心肌肥厚组小鼠心肌细胞肥大、排列紊乱、细胞核深染。心肌肥厚组小鼠左心室舒张末期直径、左心室舒张末期容积均显著低于假手术组(P0.05),而室间隔明显较假手术组增厚(P0.05)。心肌肥厚组小鼠HDACs活性显著高于假手术组(P0.05);心肌肥厚组HDAC5和β-MHC的mRNA及蛋白表达水平均显著高于假手术组(P0.05)。SAHA能够显著降低HDAC5表达水平,显著下调心脏肥厚相关基因β-MHC的表达并改善小鼠心功能和心肌肥厚(P均0.05)。结论:HDAC参与了心肌肥厚的发生,HDAC抑制剂SAHA通过抑制HDAC5的表达从而改善小鼠心肌肥厚。     

长QT综合征的分子生物学研究进展

先天性长QT综合征 (LQTS)是一种遗传性心脏病 ,共有两种形式 :Romano WardSyndrome(RWS)和JervellandLange NielsenSyndrome(JLNS)。目前已发现 5个LQTS致病基因共 177个突变位点。该 5个致病基因均是编码离子通道蛋白的基因。RWS相关基因分别是KvLQT1,HERG ,SCN5A ,minK ,MiRP1,以常染色体显性遗传为特征。KvLQT1和HERG均编码钾离子通道。KvLQT1和minK的编码蛋白形成心肌缓慢激活延迟整流钾通道。HERG和MiRP1的编码蛋白形成心肌快速激活延迟整流钾通道。两者通过负显性机制发挥作用。SCN5A编码钠离子通道 ,通过功能放大机制发挥作用。JLNS相关基因是KvLQT1或minK的纯合突变 ,以常染色体隐性遗传为特征。此外尚有未知基因与LQTS有关。     

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。     

The Na+/Ca2+ exchanger/SR Ca2+ ATPase transport capacity regulates the contractility of normal and hypertrophied feline ventricular myocytes

BACKGROUND: Pressure overload leads to cardiac hypertrophy, which is often followed by heart failure. We tested the hypothesis that depressed contractility in this process results from an imbalance in Ca 2+ transport by the sarcoplasmic reticulum (SR) Ca2+ ATPase (SERCA) and the sarcolemmal Na+/Ca2+ exchanger (NCX). METHODS AND RESULTS: Left ventricular (LV) myocytes (n = 79) from 12 normal (N) and 5 hypertrophied (LVH, by aortic banding) feline hearts were studied. Adenoviral gene transfer was used to introduce green fluorescent protein (GFP), SERCA2, and NCX into N and LVH myocytes. Contraction (videomicroscopy) and Ca2+ transients (Fluo-3) were measured in steady state and after rest periods of 2 to 120 seconds (rest decay and potentiation). LVH hearts were significantly larger than N (7.1 +/- 1.4 versus 4.2 +/- 0.2 g/kg). SERCA protein was significantly less abundant in LVH versus N. Steady state contractions and Ca2+ transients of LVH-GFP myocytes decayed more slowly and rest decay of contractility was more pronounced compared with N-GFP. Infection of LVH (and N) myocytes with SERCA increased basal contractility and reduced rest decay. Infection of LVH myocytes with NCX almost abolished contraction and in N myocytes reduced contractility and increased rest decay. CONCLUSION: These findings suggest that an imbalance of Ca2+ transport by SERCA and the NCX produces the characteristic contractile abnormalities of hypertrophied cardiac myocytes.     

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.     

Open-state unblock characterizes acute inhibition of I potassium current by amiodarone in guinea pig ventricular myocytes

INTRODUCTION: The aim of the present study was to investigate the acute action of amiodarone on the slow component of delayed rectifier K+ current (IKs) under basal conditions and during beta-adrenoceptor stimulation in guinea pig ventricular myocytes. METHODS AND RESULTS: Using the whole-cell patch-clamp method, IKs was evoked by depolarizing voltage-clamp steps, during superfusion with the Na+-, K+-, and Ca2+-free solution supplemented with 0.4 microM nisoldipine and 5 microM E-4031. The acute effect of amiodarone was evaluated, within approximately 10 minutes after starting the bath application, by the amplitude of deactivating tail currents at -50 mV. Amiodarone concentration dependently blocked I(Ks) and exerted a more potent effect on IKs when activated by shorter pulse durations; the degree of block by 30 microM amiodarone on IKs activated by 200 ms, 500 ms, and 2000 ms depolarizing pulses to +30 mV was 55.9 +/- 5.8%, 38.6 +/- 6.0%, and 27.1 +/- 4.0% (n = 5 each), respectively. An envelope of tails test conducted at +10, +30, and +60 mV demonstrated that the degree of IKs block by amiodarone was gradually attenuated during membrane depolarization, which can be described by a monoexponential function, thus supporting the presence of open channel unblock. Amiodarone also blocked IKs maximally stimulated by 1 microM isoprenaline, to an extent similar to control, when IKs was activated by pulse durations of < or =2000 ms. CONCLUSION: We propose that amiodarone acutely blocks native IKs with characteristics associated with open channel unblock, and that the protein kinase A-mediated phosphorylation of channel proteins only minimally affects the amiodarone block.     

高血压左室肥厚消退后心肌细胞跨膜电位变化的实验研究

目的　观察高血压左室肥厚消退后心肌细胞跨膜电位的变化。方法　 12周龄自发性高血压大鼠 (SHR) ,分别饲服尼群地平或卡托普利 14周 ,以同龄WKY及不经治疗的SHR鼠为对照。采用传统浮置式玻璃微电极记录在体心脏心室肌细胞的动作电位幅度 (APA) ,静息电位 (RMP) ,动作电位时限 (APD) ,及复极 90 %、75 %、5 0 %、2 5 %时的动作电位时限 (APD90 、APD75 、APD5 0 、APD2 5 ) ,并计算APD的离散度。结果　 (1)左室肥厚心肌细胞APD及其离散性均明显大于对照组 ;(2 )尼群地平和卡托普利治疗消退左室肥厚后 ,左心室肌细胞APD缩短及APD离散性减少。结论　伴随心肌肥厚的消退 ,心室肌细胞电生理异常好转。     

Temporal patterns of electrical remodeling in canine ventricular hypertrophy: focus on IKs downregulation and blunted beta-adrenergic activation

OBJECTIVES: Electrical remodeling in cardiac hypertrophy often involves the downregulation of K+ currents, including beta-adrenergic (beta-A)-sensitive IKs. Temporal patterns of ion-channel downregulation are poorly resolved. In dogs with complete atrioventricular block (AVB), we examined (1) the time course of molecular alterations underlying IKs downregulation from acute to chronic hypertrophy; and (2) concomitant changing responses of repolarization to beta-adrenergic receptor (beta-AR) stimulation. METHODS AND RESULTS: Serial left-ventricular (LV) biopsies were collected from anesthetized dogs during sinus rhythm (SR; control) and at 3, 7 and 30 days of AVB. KCNQ1 mRNA and protein decreased within 3 days (protein expression 58 +/- 10% of control), remaining low thereafter. beta1-AR mRNA and protein decreased more gradually to 53 +/- 8% at 7 days. In chronic-AVB LV myocytes, IKs -tail density was reduced: 1.4 +/- 0.3 pA/pF versus 2.6 +/- 0.4 pA/pF in controls. beta-A enhancement of IKs was reduced. Isoproterenol shortened action-potential duration in control cells, while causing heterogeneous repolarization responses in chronic AVB. beta-A early afterdepolarizations were induced in 4 of 13 chronic-AVB cells, but not in controls. In intact conscious dogs, isoproterenol shortened QTc at SR (by -8 +/- 3% from 295 ms), left it unaltered at 3 days AVB (+1 +/- 3% from 325 ms) and prolonged QTc at 30 days (+6 +/- 3% from 365 ms). CONCLUSIONS: Profound decrease of KCNQ1 occurs within days after AVB induction and is followed by a more gradual decrease of beta1-AR expression. Downregulation and blunted beta-A activation of IKs contribute to the loss of beta-A-induced shortening of ventricular repolarization, favoring proarrhythmia. Provocation testing with isoproterenol identifies repolarization instability based on acquired channelopathy.     

芍药苷对心脏钾通道电生理功能的影响

目的研究芍药苷对内向整流钾电流(IK1)、瞬时外向钾电流(Ito)以及延迟整流钾电流(IKs和IKr)的作用。方法用全细胞膜片钳技术记录大鼠心室肌细胞的Ito和IK1电流。而IKs和IKr电流在转染相应质粒的HEK293细胞上记录。对比芍药苷使用前后的电流图,观察芍药苷对各种离子通道电流的影响。结果在-100mV测试电压下,100μmol/L的芍药苷能使IK1峰值密度从(-25.26±8.21)pA/pF降至(-17.65±6.52)pA/pF,平均抑制率为30.13%(n=6,P<0.05),但对其反转电位以及内向整流特性无影响。此外,100μmol/L芍药苷对Ito、IKs和IKr电流无明显作用。结论芍药苷对IK1电流具有明显的抑制作用,而对Ito、IKs及IKr无明显作用。     

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.     

The ionic mechanisms of long QT interval in diabetic rabbits

Objective Abnormal QT prolongation associated with arrhythmias is considered the major cardiac electrical disorder and a significant predictor of mortality in diabetic patients. The precise ionic mechanisms for diabetic QT prolongation remained unclear. The present study was designed to analyze the changes of ventricular repolarization and the underlying ionic mechanisms in diabetic rabbit hearts. Methods Diabetes was induced by a single injection ofalloxan （145mg/kg, Lv. ）. After the development of diabetes （10 weeks）, ECG was measured. Whole-cell patch-clamp technique was applied to record the action potential duration （APD50, APD90）, slowly activating outward rectifying potassium current （IKs）, L-type calcium current （ICa-L） and inward rectifying potassium current （IK1）. Results The action potential duration （APD50 and APD90） of ventricular myocytes was obviously prolonged from 271.5＋32.3 ms and 347.8＋36.3 ms to 556.6~72.5 ms and 647.9~72.2 ms respectively （P〈 0.05）. Meanwhile the normalized peak current densities of IKs in ventricular myocytes investigated by whole-cell patch clamp was smaller in diabetic rabbits than that in control group at test potential of＋50mV （1.27~0.20 pA/pF vs 3.08~0.67 pA/pF, P〈0.05）. And the density of the ICa-L was increased apparently at the test potential of 10 mV （-2.67~0.41 pA/pF vs -5.404-1.08 pA/pF, P〈0.05）. Conclusion Ventricular repolarization was prolonged in diabetic rabbits, it may be partly due to the increased L-type calcium current and reduced slow delayed rectifier K＋ current （IKs） （J Geriatr Cardio12010; 7：25-29）.