抗心律失常药物作用的新靶点--M3-R/IKM3

目的　研究心脏M3受体 /M3受体介导的钾通道与心律失常的关系,寻找抗心律失常药物的新靶点。方法分别以结扎大鼠左冠状动脉前降支所致急性心律失常模型和膜片钳技术为基础,观察M3受体的干预作用及作用机制。结果　M3受体阻断剂 4DAMP(4 diphenylacetoxy N methylpiperidine methiodide)加重结扎大鼠冠状动脉前降支所致心律失常,而M3受体激动剂胆碱能明显对抗其作用。其他亚型受体阻断剂,M1受体阻断剂 (prienzepine)、M2受体阻断剂(methotramine)和M4受体阻断剂 (tropicamide)对结扎大鼠左冠状动脉前降支所致急性心律失常无影响。在膜片钳实验中发现,胆碱可激活一种延迟整流钾电流(IKM3 ),此电流可被M3受体阻断剂 4DAMP明显抑制。而M1,M2和M4受体阻断剂对胆碱介导的电流无作用。结论　胆碱通过激动心肌M3受体诱发一外向钾电流 (IKM3 ),并在维持心脏离子通道平衡中起重要作用。M3受体 /IKM 可能是抗心律失常新靶点。     

2型糖尿病大鼠膀胱M_3受体改变的实验研究

目的研究病程3周的2型糖尿病大鼠膀胱M3受体含量及其基因转录水平的变化情况,探讨糖尿病性膀胱早期发病机制中逼尿肌M3受体的改变情况。方法2 d龄雌性Wistar大鼠随机分成2型糖尿病组和正常对照组,链脲佐菌素按90 mg/kg体重腹腔注射并结合高糖高脂饮食诱导2型糖尿病大鼠模型。于糖尿病病程3周时进行下列实验:反转录-聚合酶链反应(RT-PCR)方法检测M3受体mRNA的含量;Western blotting方法检测膀胱M3受体蛋白的含量。结果RT-PCR方法检测结果显示:糖尿病组大鼠膀胱M3受体mRNA的数量显著高于正常对照组[(52.0±5.7)%vs(35.6±11.7)%,P<0.05]。Western blotting方法检测结果显示:糠尿病组大鼠膀胱M3受体含量显著高于正常对照组[(30.9±2.1)%vs(23.4±4.7)%,P<0.01]。结论本研究证实了糖尿病性膀胱早期M3受体的生物合成上调这一改变,从而解释了糖尿病早期膀胱逼尿肌收缩力增加这一现象。这可能是早期糖尿病性膀胱病变的一个发病机制。     

KCNQ2/3钾通道电流特征及M_1受体的调节作用

目的观察KCNQ2/3通道电流特征及M1受体激活对该电流的调节作用。方法以CHO细胞作为表达体系,用脂质体共转染KCNQ2、KCNQ3钾离子通道及毒蕈碱型M1受体。全细胞膜片钳方法,观察KCNQ2/3电流特征,药理学阻断剂的作用及M1受体激活对电流的调节。结果KC-NQ2/3电流呈现慢激活、低阈值、非失活、电压依赖性的外向钾离子电流特点,其激活电压的阈值在-60 mV,半数激活电压值(-26.8±1.2)mV,其去活曲线可用双指数方程拟合,fτast约101 m s;sτlow约为309 m s。该电流对4-AP,Ba2+,TEA不敏感,L inop ird ine抑制KCNQ2/3电流IC50为(6.5±0.83)μmol.L-1。乙酰胆碱激活M1受体后会可逆性地抑制KCNQ2/3电流,其抑制的IC50为(0.7±0.05)μmol.L-1。结论KCNQ2/3通道作为神经细胞M通道的分子基础,其电流特征与M电流一致,L inop ird ine对其有较强阻断作用,神经递质乙酰胆碱通过激活M1受体明显抑制该通道电流。研究KCNQ2/3通道电流特征及受体调节规律,对于理解与中枢兴奋性有关的疾病如:惊厥、癫痫、阿尔采末病等发生机制有重要指导意义。     

匹维溴胺对束缚应激大鼠结肠不同部位和肌层平滑肌条的作用

目的评价匹维溴胺对束缚应激大鼠离体结肠平滑肌条的影响并探讨其对各型IBS可能的作用机理.方法成年SD大鼠随机分为模型组和对照组,模型组用自制硬塑胶模具束缚 2 h.分别制作两组大鼠近端及远端结肠的环行肌和纵行肌条共64条(每组肌条32个,各肌层8个).采用离体平滑肌条器官浴槽实验方法,观察不同浓度匹维溴胺对平滑肌条自发性收缩活动的影响.结果匹维溴胺对模型组和对照组离体结肠平滑肌条自发性收缩活动均表现为抑制作用,但对模型组效应较对照组显著(近端结肠 28.54±4.82 vs 7.48±1.65,21.75±1.00 vs 12.56±3.15;远端结肠 15.71±5.27 vs 3.89±1.16,20.16±3.16 vs 7.56±1.96)(P<0.05).匹维溴胺对近端结肠平滑肌收缩的抑制作用较远端结肠显著(P<0.05).匹维溴胺对相同部位结肠环行肌与纵行肌的抑制作用无显著性差异(P>0.05).结论匹维溴胺能抑制束缚应激大鼠离体结肠平滑肌的收缩,且对近端结肠收缩的抑制作用显著高于远端结肠;但在相同部位,对环行肌和纵行肌收缩的抑制作用无显著性差异.     

慢性心房颤动犬心房组织肾素-血管紧张素系统的表达及意义

目的探讨肾素-血管紧张素系统(RAS)在慢性心房颤动犬心房组织中的表达及意义。方法健康杂种犬16条,随机分为正常对照组8条,单纯心房颤动起搏组8条。心房颤动组植入埋藏式高频率心脏起博器(500±20)次/min,起博24周后处死动物,分别于左、右心房取材,采用免疫组织化学检测心房组织中肾素-血管紧张素转化酶(ACE)、血管紧张素Ⅱ1型受体(AT1R)以及肾素-血管紧张素转化酶抑制剂(ACEI)的表达变化。正常对照组未植入起搏器,与心房颤动组同步行相应检查。结果与对照组比较,心房颤动组心房组织中ACE和AT1R表达水平显著增强,而ACEI的表达水平明显下降,各组间比较差异有统计学意义(P<0.01)。结论慢性心房颤动犬心房组织RAS的激活参与了心房颤动的形成,可能是心房颤动发生、发展的主要机制之一。     

苦参碱对肾移植大鼠静脉血IL-2的影响

目的:研究苦参碱(matrine,Mat)对肾移植大鼠存活时间、血尿素氮(BUN)和血清肌酸酐(SCr)及白细胞介素-2(IL-2)的影响,探讨苦参碱(Mat)免疫抑制作用的可能机制。方法:实验共分5个组:生理盐水组(NS组)、苦参碱组(Mat组)、环孢素A组(CsA组)、苦参碱+环孢素A组(M at+CsA组)和同基因对照组,采用Kamada方法行SD→Wistar大鼠单肾原位移植建立同种异基因肾移植急性排斥反应实验动物模型及Wistar→Wistar建立同种同基因对照组模型,观测术后受体鼠的存活时间及外周血BUN和SCr水平;ELISA法检测受体鼠外周血IL-2水平。结果:对照组受体鼠术后均长期存活,并超过100 d;NS组受体大鼠平均生存(6.83±0.75)d;Mat组存活时间为(10.16±1.17)d,CsA组存活时间为(11.50±1.05)d;Mat与CsA联合应用后,可明显延长受体鼠的存活时间至17 d以上(20.33±2.58)d,Mat组受体鼠外周血IL-2水平低于NS组,而M at+CsA组受体鼠IL-2水平明显低于M at组和CsA组。结论:M at对大鼠肾移植的急性排斥反应具有一定的抑制作用,并与低剂量CsA联用产生显著的协同效应。M at免疫抑制作用机制可能是抑制Th1细胞产生IL-2,与CsA的作用机制相似。     

微RNA-27a介导3T3-L1脂肪细胞胰岛素抵抗的作用机制

目的研究微 RNA?27a(miR?27a)介导 3T3?L1脂肪细胞胰岛素抵抗的作用机制。方法将 3T3?L1细胞诱导分化为脂肪细胞,采用肿瘤坏死因子 ?α(TNF?α)法建立 3T3?L1脂肪细胞的胰岛素抵抗模型,检测 miR?27a对 3T3?L1细胞葡萄糖摄取的影响,蛋白质印迹法(Western Blot)检测 miR?27a对胰岛素信号通路的影响。实时荧光定量多聚核苷酸链式反应(qPCR)及双荧光素酶报告基因检测法检测 miR?27a的作用靶点。结果 miR?27a介导了 3T3?L1脂肪细胞的胰岛素抵抗［正常对照组,模型组, miR?27a mimics+模型组, miR?27a inhibitor+模型组四组的吸光度值分别为(2.03±0.20)(1.28±0.27)(1.43±0.20)(1.97± 0.18)P＜0.01］的磷酸qPCR?27a抑过氧化物酶体增殖物激活受体 γ(PPARγ)的表达［对照组和 mir?27a组的相对值分别为(1.00±0.08)和(0.59± 蛋白质印迹法显示miR?27a抑制了胰岛素信号通路中胰岛素受体底物1(IR,S1)及Akt蛋白,化。,显示miR,制了,0.14)P＝0.0048］,双荧光素酶报告基因检测验证了 PPARγ为miR?27a的作用靶点［PPARγ WT+miR?NC,PPARγ WT+miR?27a, Mut+miR?NC,PPARγ Mut+miR?27a四组的相对荧光值分别为(5.37±0.80)、(3.17±0.57)、(4.94±0.63)、(4.68±0.74),P＜PPARγ,0.01］。结论 miR?27a通过抑制胰岛素信号通路及靶向 PPARγ介导 3T3?L1细胞胰岛素抵抗。     

N-甲基小檗胺对人心房肌细胞瞬时外向钾电流和延迟整流钾电流的作用(英文)

目的　动物实验表明N 甲基小檗胺 (NMB)通过抑制豚鼠心室肌细胞ATP敏感性钾电流和钙电流来发挥抗心律失常和抗心肌缺血作用 ,故进一步研究NMB对人心肌细胞电流的作用。方法　膜片钳制技术全细胞记录模式研究NMB对人心房肌细胞瞬时外向钾电流 (Ito)和延迟整流钾电流 (IK)的作用。结果　指令电位为 +60mV时 ,NMB 0 .1 ,1 ,1 0 μmol·L-1 分别使Ito幅值下降 (1 6± 4) % ,(2 5±4) %和 (49± 3) % ,使IK 幅值下降 (42± 6) % ,(47±7) %和(65± 3) %。结论　NMB对人心房肌细胞Ito和IK 均有抑制作用。     

苯环喹溴铵的毒蕈碱样乙酰胆碱受体亚型选择性研究

目的探讨苯环喹溴铵对毒蕈碱样乙酰胆碱受体(M受体)亚型的选择性。方法以表达单一M受体亚型的CHO细胞株进行细胞与[3H]-QNB的饱和实验,并进行竞争抑制药和[3H]-QNB与M受体亚型的竞争结合实验,计算Kd值和Ki值。通过离体膀胱肌条实验评价苯环喹溴铵干预乙酰胆碱对离体膀胱肌条的收缩作用,计算pA2值。观察苯环喹溴铵对麻醉犬心率、心电图的影响及其对小鼠气管分泌功能的影响。结果苯环喹溴铵对3种细胞的抑制强度为CHOM3>CHOM1>CHOM2,对CHOM3和CHOM1的抑制能力相似,明显高于对CHOM2的抑制能力(P<0.01)。苯环喹溴铵可拮抗乙酰胆碱对离体膀胱肌条的收缩作用,使量效曲线平行右移,PA2值为7.09±s0.06。与溶媒组相比,苯环喹溴铵经鼻给药后对麻醉犬的心率和心电图无明显影响(P>0.05)。苯环喹溴铵大剂量组给药后1h、2h和中剂量组给药后2h能明显减少小鼠气管分泌物的分泌(P<0.01)。结论苯环喹溴铵是一种可选择性作用于M1和M3受体亚型的拮抗药。     

血管紧张素Ⅱ2型受体对人房颤心房细胞的影响——对心房肌细胞瞬间外向钾离子通道的作用

目的 研究血管紧张素Ⅱ2型受体(AT2)对单个人心房颤动心房肌细胞瞬间外向钾电流(Ⅰtol)的影响.方法 选择择期行心脏体外循环手术的持续性心房颤动(＞6个月)患者,建立体外循环前取有心耳组织约0.3 cm3,放入氧饱和的4℃心脏停搏液中,5 min内送同实验室.用胶原酶Ⅱ两步酶解法分离出单个心房肌细胞,用标准的全绌胞膜片钳技术记录瞬间外向钾电流,观察0.5 mmol/L CGP 42112及0.5 mmol/L PD 123319引起单个人心房颤动心房肌细胞瞬间外向钾电流(Ⅰtol)改变.结果 窦律空白对照组Itol峰值电流密度为(12.73±7.75)pA/pF(n=7),房颤空白对照组Ⅰtol峰值电流密度为(4.42±1.62)pA/pF(n=8),心房颤动空白对照组Ⅰtol峰值电流密度明显降低(P＜0.05).CGP42112灌流前后律组及心房颤动组Ⅰtol峰值电流密度无明显变化(P＞0.05);PD 123319灌流不影响安律组及心房颤动组Ⅰtol峰值电流密度(P＞0.05).结论 心房颤动患者心房肌细胞Ⅰtol电流密度较窦律患者减少,心房颤动致Ⅰtol通道的电牛理特性改变.AT2受体激活和欠活均不改变窦律患者和心房颤动患者心房肌细胞Ⅰtol通道电流密度,表明Ⅰtol的下调小完全通过AT2介导.     

犬心房肌细胞的分离及外向钾通道电流的记录

目的：探讨犬心房肌细胞的分离方法及其通道电流记录.方法：采用冠状动脉灌流、酶解技术分离犬心房肌细胞,应用膜片钳全细胞记录技术,记录细胞膜快速延迟整流钾电流（Ikr）、缓慢延迟整流钾电流（Iks）、超快延迟整流钾电流（Ikur）及瞬时外向钾电流（Ito）.结果：获得具有正常电生理活性的单个心房肌细胞,成功记录了Ikr、Iks、Ikur及Ito.结论：此方法分离的单个心房肌细胞具有正常的电生理活性,可用于研究心房肌细胞离子通道特征.     

碘化N-正丁基氟哌啶醇对豚鼠心房肌细胞乙酰胆碱敏感性钾通道的影响

目的研究碘化N正丁基氟哌啶醇(F2)对豚鼠心房肌细胞乙酰胆碱敏感性钾通道(KACh)的影响,探讨其对KACh的作用机制。方法采用膜片钳全细胞记录方法,测定F2对原代培养的豚鼠心房肌细胞乙酰胆碱敏感性钾电流IK(ACh)的影响。结果细胞外给予F2对豚鼠心房肌细胞IK(ACh)呈可逆性、浓度依赖性的阻断作用。细胞内添入抗水解的GTP类似物GTPγS后,结果同前。细胞内给予50μmol·L-1F2对IK(ACh)无作用。结论F2是豚鼠心房肌细胞KACh的一种快速通道阻断剂,发挥作用部位在细胞膜外侧,作用位点在钾通道本身,与乙酰胆碱受体无关。     

Effects of NIP-141 on K currents in human atrial myocytes.

A novel benzopyran derivative, NIP-141, effectively terminates experimental atrial fibrillation in canine hearts by prolonging atrial refractoriness. However, the effects of this drug on human atrial myocytes are unknown. This experiment evaluated the effects of NIP-141 on K currents in isolated human atrial myocytes using a whole-cell voltage-clamp method. NIP-141 inhibited the transient outward current (I(to)) and the ultra-rapid delayed rectifier K current (I(Kur)), each in a dose-dependent manner, with half-maximal inhibition concentrations of 16.3 microM and 5.3 microM, respectively (n = 5). NIP-141 inhibited both K currents in a voltage- and use-independent fashion, and it preferentially blocked them in the open state and dissociated rapidly from the channel. Because both K currents contribute significantly to the repolarization of the atrial action potential, these findings suggest that NIP-141 may terminate atrial fibrillation by prolonging action potential duration.     

苦参碱对缺血性心室肌细胞快速延迟整流钾电流的作用

目的观察苦参碱对病理条件下(缺血、酸中毒)单个心室肌细胞快速延迟整流钾电流(rapid component of delayed rectifier potassium current,IKr)的作用,初步探讨苦参碱治疗缺血性心律失常的作用机制。方法冠状动脉左前降支结扎建立家兔心肌梗死模型,应用全细胞膜片钳技术记录酶解法分离的心肌梗死模型家兔苦参碱灌胃1mon后右心室心肌细胞IKr的变化。在pH=7·4和pH=6·5的条件下,应用全细胞膜片钳技术记录苦参碱对酶解法分离的豚鼠心室肌细胞IKr的作用。结果在正常细胞外液(pH=7·4)的条件下苦参碱(50μmol·L-1)降低IKr,在刺激电压为+60mV时,IKr电流密度由(12·15±0·70)pA/pF降低至(9·22±0·65)pA/pF(n=8,P<0·05)。在细胞外液酸化(pH=6·5)的条件下苦参碱(50μmol·L-1)仍表现抑制IKr电流的作用,在刺激电压为+60mV时,IKr电流密度由(7·05±0·41)pA/pF降低至(5·76±0·28)pA/pF(n=8,P<0·05)。家兔冠状动脉结扎1mon后,在刺激电压为+60mV时,心肌梗死组家兔心室肌细胞IKr电流密度为(1·17±0·12)pA/pF较正常组(1·70±0·11)pA/pF降低(n=12,P<0·05)。苦参碱组(8mg·kg-1·d-1)家兔心室肌细胞IKr电流密度为(0·86±0·25)pA/pF较心梗组降低(n=12,P<0·05)。结论苦参碱阻断心室肌细胞IKr,可能是其延长有效不应期,降低异位节律的发生率,治疗心律失常的机制之一。苦参碱对酸化条件及长期心肌缺血后心室肌细胞IKr仍表现出明显的抑制作用,表明其对心肌梗死后心律失常有效。     

Electrophysiological effects of ketamine on human atrial myocytes at therapeutically relevant concentrations

1. Ketamine is widely used for the induction of anaesthesia in high-risk patients with cardiovascular instability or severe hypovolaemia. However, the ionic mechanisms involved in the effects of ketamine at therapeutically relevant concentrations in human cardiac myocytes are unclear. The present study was designed to investigate the effects of ketamine on L-type Ca2+ (I(Ca)), transient outward K+ (I(to)), ultra-rapid delayed rectifier K+ (I(Kur)) and inward rectifier potassium (I(K1)) currents, as well as on action potentials, in human isolated atrial myocytes. 2. Atrial myocytes were isolated enzymatically from specimens of human atrial appendage obtained from patients undergoing coronary artery bypass grafting. The action potential and membrane currents were recorded in both current- and voltage-clamp modes using the patch-clamp technique. 3. Ketamine inhibited I(Ca) with an IC(50) of 1.8 micromol/L. In addition, 10 micromol/L ketamine decreased the I(Ca) peak current at +10 mV from 5.1 +/- 0.3 to 2.1 +/- 0.4 pA/pF (P < 0.01), but did not change the threshold potential, peak current potential and reverse potential. 4. Ketamine had no effect on I(to), I(Kur) or I(K1), but it reversibly shortened the duration of the action potential in human atrial myocytes. 5. In conclusion, ketamine, at a clinically relevant concentration, shortens the action potential duration of the human atrial myocytes, probably by inhibiting I(Ca).     

Inhibition of IK,ACh current may contribute to clinical efficacy of class I and class III antiarrhythmic drugs in patients with atrial fibrillation

Inward rectifier potassium currents I_K1 and acetylcholine activated I_K,ACh are implicated in atrial fibrillation (AF) pathophysiology. In chronic AF (cAF), I_K,ACh develops a receptor-independent, constitutively active component that together with increased I_K1 is considered to support maintenance of AF. Here, we tested whether class I (propafenone, flecainide) and class III (dofetilide, AVE0118) antiarrhythmic drugs inhibit atrial I_K1 and I_K,ACh in patients with and without cAF. I_K1 and I_K,ACh were measured with voltage clamp technique in atrial myocytes from 58 sinus rhythm (SR) and 35 cAF patients. The M-receptor agonist carbachol (CCh; 2 μM) was employed to activate I_K,ACh. In SR, basal current was not affected by either drug indicating no effect of these compounds on I_K1. In contrast, all tested drugs inhibited CCh-activated I_K,ACh in a concentration-dependent manner. In cAF, basal current was confirmed to be larger than in SR (at −80 mV, −15.2 ± 1.2 pA/pF, n = 88/35 vs. −6.5 ± 0.4 pA/pF, n = 194/58 [myocytes/patients]; P < 0.05), whereas CCh-activated I_K,ACh was smaller (−4.1 ± 0.5 pA/pF vs. −9.5 ± 0.6 pA/pF; P < 0.05). In cAF, receptor-independent constitutive I_K,ACh contributes to increased basal current, which was reduced by flecainide and AVE0118 only. This may be due to inhibition of constitutively active I_K,ACh channels. In cAF, all tested drugs reduced CCh-activated I_K,ACh. We conclude that in cAF, flecainide and AVE0118 reduce receptor-independent, constitutively active I_K,ACh, suggesting that they may block I_K,ACh channels, whereas propafenone and dofetilide likely inhibit M-receptors. The efficacy of flecainide to terminate AF may in part result from blockade of I_K,ACh.     

冬虫夏草水提液对单个心室肌细胞钾通道的影响

目的　观察冬虫夏草水提液对豚鼠及大鼠心室肌细胞钾通道的作用 ,探讨冬虫夏草的抗心律失常作用机制。方法　应用全细胞膜片钳技术记录冬虫夏草水提物对豚鼠单个心室肌细胞内向整流钾电流 (IK1)、延迟整流钾电流 (IK)及大鼠心室肌细胞瞬时外向钾电流 (Ito)的影响。结果　应用 0 1g·L-1(生药浓度 )冬虫夏草水提液使豚鼠单个心室肌细胞内向整流钾电流在实验电压 - 12 0mV时从给药前(- 36 37± 5 15 ) pA/pF减少到 (- 2 9 70± 5 90 ) pA/ pF(n=5 ,P <0 0 5 ) ;延迟整流钾电流在实验电压 +70mV时 ,从给药前 (9 2 1± 2 4 2 ) pA/ pF增加至 (11 5 4± 2 98)pA/ pF(n =6 ,P <0 0 1) ;使大鼠心室肌细胞瞬时外向钾电流 (Ito)在实验电压 +5 0mV时 ,从给药前 (13 36± 0 88) pA/ pF增加至 (16 4 8± 1 0 9) (n =4 ,P <0 0 1)。结论　冬虫夏草抗心律失常作用与它对心肌细胞钾通道的作用有关。它增加IK,Ito的同时抑制IK1,将会使动作电位时程缩短而不至于发生早后除极和迟后除极     

Inhibitory effects of aprindine on the delayed rectifier K+ current and the muscarinic acetylcholine receptor-operated K+ current in guinea-pig atrial cells

In order to clarify the mechanisms by which the class Ib antiarrhythmic drug aprindine shows efficacy against atrial fibrillation (AF), we examined the effects of the drug on the repolarizing K+ currents in guinea-pig atrial cells by use of patch-clamp techniques. We also evaluated the effects of aprindine on experimental AF in isolated guinea-pig hearts. Aprindine (3 microM) inhibited the delayed rectifier K+ current (IK) with little influence on the inward rectifier K+ current (IK1) or the Ca2+ current. Electrophysiological analyses including the envelope of tails test revealed that aprindine preferentially inhibits IKr (rapidly activating component) but not IKs (slowly activating component). The muscarinic acetylcholine receptor-operated K+ current (IK.ACh) was activated by the extracellular application of carbachol (1 microM) or by the intracellular loading of GTPgammaS. Aprindine inhibited the carbachol- and GTPgammaS-induced IK.ACh with the IC50 values of 0.4 and 2.5 microM, respectively. In atrial cells stimulated at 0.2 Hz, aprindine (3 microM) per se prolonged the action potential duration (APD) by 50+/-4%. The drug also reversed the carbachol-induced action potential shortening in a concentration-dependent manner. In isolated hearts, perfusion of carbachol (1 microM) shortened monophasic action potential (MAP) and effective refractory period (ERP), and lowered atrial fibrillation threshold. Addition of aprindine (3 microM) inhibited the induction of AF by prolonging MAP and ERP. We conclude the efficacy of aprindine against AF may be at least in part explained by its inhibitory effects on IKr and IK.ACh.     

Effects of azimilide on the muscarinic acetylcholine receptor-operated K+ current and experimental atrial fibrillation in guinea-pig hearts

Effects of azimilide, a class III antiarrhythmic drug, on the acetylcholine (ACh) receptor-operated K+ current (I K.ACh) and the delayed rectifier K+ current (IK) were examined in guinea-pig atrial cells using patch-clamp techniques. Effects of azimilide on experimental atrial fibrillation (AF) were also examined in isolated guinea-pig hearts. In single atrial myocytes, azimilide inhibited both the rapid (IKr) and slow component of IK (IKs). Azimilide inhibited the I K.ACh induced by carbachol (CCh, 1 microM), adenosine (10 microM), and intracellular loading of GTPgammaS (100 microM) in a concentration-dependent manner. The IC50 values of azimilide for inhibiting the CCh-, adenosine-, and GTPgammaS-induced I K.ACh were 1.25, 29.1, and 20.9 microM, respectively, suggesting that azimilide inhibits I K.ACh mainly by blocking the muscarinic receptors. Azimilide concentration-dependently (0.3 - 10 microM) prolonged the action potential duration (APD) in the absence and presence of muscarinic stimulation. In isolated hearts, perfusion of CCh shortened the duration of the monophasic action potential (MAP) and effective refractory period (ERP) of the left atrium and lowered the atrial fibrillation threshold (AFT). Addition of azimilide inhibited the induction of AF by prolonging the duration of MAP and ERP. The I K.ACh inhibition by azimilide may at least in part contribute to the effectiveness to prevent parasympathetic-type AF.     

Effects of a new class III antiarrhythmic drug nibentan in a canine model of vagally mediated atrial fibrillation

Nibentan, a new class III antiarrhythmic drug, is highly effective in patients with atrial flutter and fibrillation. However, its mechanism of action remains unclear. The aim of this study was to investigate the effects of nibentan using a canine model of vagally sustained atrial fibrillation (AF). Nibentan was intravenously infused to anesthetized open-chest dogs during vagally induced AF. Cumulative doses of nibentan (0.063, 0.125, and 0.250 mg/kg) successfully terminated AF in 78, 88, and 100% as well as prevented AF reinduction in 11, 63, and 90% of cases, respectively. All doses of nibentan significantly and rate-independently increased atrial effective refractory period (AERP) with and without vagal stimulation. Activation mapping (224 epicardial electrodes) during AF showed that nibentan reduced the number of simultaneously occurring reentrant wavelets. Herewith the atrial excitation slowed down until conduction failure of reentrant wavelets led to arrhythmia termination. These changes in activation patterns can be accounted for by nibentan-induced increase of AERP (55 +/- 9%, 82 +/- 12%, and 90 +/- 6%; p < 0.01) and wavelength for reentry (47 +/- 7%, 68 +/- 12%, and 72 +/- 4%; p < 0.01) at rapid atrial rates in the presence of vagal stimulation. In conclusion, the high efficacy of nibentan against AF was associated with significant rate-independent increase in AERP and in wavelength, and might be in part explained by block of both delayed rectifier (I(K)) and muscarinic I(K,ACh) currents.