Angiotensin II Receptor Regulates Ionic Currents in Guinea Pig Ventricular Myocytes

BACKGROUND: Previous studies have shown that angiotensin II (Ang II) receptors are preset in a wide variety of target tissues and that Ang II regulates the target tissue functions through Ang II receptors. However, the action of Ang II receptors on transsarcolemmal currents in ventricular myocytes has not been elucidated. METHODS AND RESULTS: We performed whole-cell voltage clamp and patch clamp experiments to determine the effects of Ang II-receptor agonists and antagonists on ionic currents in single isolated guinea pig ventricular myocytes. We found that extracellular perfusion of Ang II (30 nM) increased the L-type Ca(2+) current from 581 +/- 27 to 837 +/- 42 pA (n = 5, P <.01). Ang II also prolonged the Ca(2+) current activation and inactivation time constants. These were reversible by losartan (100 nM), a type 1 Ang II receptor (AT(1)) blockade. On the other hand, perfusion of 30 nM Ang II decreased K(+) current (I(K)) from 1543 +/- 28 to 1194 +/- 50 pA (n = 5, P <.05) and K(+) tail current (I(K-tail)) from 275 +/- 24 to 206 +/- 29 pA (n = 5, P <.05). These effects were also abolished by perfusion of losartan. However, perfusion of Ang II resulted in an increase of inward rectified K(+) current (I(K1)) in whole-cell recordings. Single channel recordings showed that the increase in I(K1) was attributed to a burst opening current with a larger unit of amplitude. These effects were reversed by saralasin but not losartan, indicating possible type 2 Ang II receptor (AT(2)) involvement. CONCLUSIONS: Our results provide evidence that Ang II receptors regulate the transsarcolemmal currents in single guinea pig ventricular myocytes. Therefore, Ang II regulation of ionic currents is mediated through the different subtypes of Ang II receptors.     

山莨菪碱对兔心室肌细胞离子通道电流的影响

目的研究山莨菪碱对兔正常离体心室彤睫田胞离子通道电流的影响,探讨其抗心律失常的细胞学离子机制。方法以酶解的方法分离兔心室肌外膜单个心室肌细胞,采用全细胞膜片钳技术,研究不同浓度山莨菪碱对兔正常心室肌细胞跨膜钠离子通道电流（INa）、L-钙通道电流（ICa-L）及瞬间外向钾通道电流（Ito）的影响。结果山莨菪碱浓度为10nmol／L时,对INa无明显影响（P〉0．05）。山莨菪碱浓度为100nmol／L时,INa电流密度减少到（-33．25&#177;4．46）pA／pF,1000nmol／L时INa电流密度减少到（-29．32&#177;3．55）pA／pF,抑制率分别为22．3％和31．5％,与基础值比较,差异均有统计学意义（P〈0．01）。山莨菪碱浓度为10nmol／L时,对ICa-L无明显影响（P〉0．05）。山莨菪碱浓度为100nmol／L时,ICa-L．电流密度减少到（-2．15&#177;1．02）pA／pF,1000nmol／L时ICa-L电流密度减少到（-1．82&#177;0．86）pA／pF,抑制率分别为31．3％和41．8％,与基础值比较,差异均有统计学意义（P〈0．01）。山莨菪碱浓度为10nmol／L时,Ito电流密度由（17．41&#177;3．13）pA／pF减少到（16．13&#177;2．93）pA／pF,100nmol／L时减少到（15．11&#177;2．88）pA／pF,1000nmol／L时减少到（14．96&#177;2．82）pA／pF,抑制率分别为7．3％、13．2％和14．1％,均无统计学差异（P〉0．05）。结论山莨若碱对离体正常单个心室肌细胞INa和ICa-L具有剂量依赖性抑制作用。     

楸毒素对豚鼠离体心脏QT间期延长的作用研究

目的观察楸毒素(MTX)豚鼠离体心脏QT间期的影响,探究楸毒素对豚鼠离体心脏的作用。方法采用Langendorff逆行主动脉灌流法灌流6只豚鼠离体心脏。分别记录正常和给予楸毒素后的豚鼠心电图,测量心肌电生理指标。结果灌流结果显示,给予0.4μmol/L的楸毒素能显著缩短QT间期,从171.92±6.91ms缩短至142.96±5.89ms,缩短近16.85%,差异有统计学意义(P0.01);Tp-e有显著缩短,缩短约25.68%,差异有统计学意义(P0.05)。多非利特显著延长豚鼠心电图的QT间期;给予多非利特(Dofetilide,Do)后,再分别给予低中高三个浓度(0.2μmol/L、0.4μmol/L和0.6μmol/L)MTX,相比Do组,低浓度MTX对QT和Tp-e差异无统计学意义(P0.05);0.4μmol/L和0.6μmol/LMTX能够逆转多非利特的延长作用。结论楸毒素能缩短心脏的QT间期,对抗多非利特诱导的豚鼠离体心脏LQT2,对心律失常起治疗作用。     

Modulation of the Electrophysiologic Actions of E-4031 and Dofetilide by Hyperkalemia and Acidosis in Rabbit Ventricular Myocytes

BACKGROUND: E-4031 and dofetilide are new class III antiarrhythmic agents that inhibit the rapid component of the delayed rectifier potassium channel (I(Kr)); however, the effectiveness of many antiarrhythmic drugs in ischemic conditions is uncertain. METHODS AND RESULTS: We modeled two components of ischemia, hyperkalemia (9.6 mM) and acidosis (pH 6.8), in voltage-clamped single rabbit ventricular myocytes to help determine the effect of ischemia on the action of these two drugs. In physiologic solution both E-4031 and dofetilide blocked I(Kr) and significantly reduced total outward current. In hyperkalemic solution, both E-4031 and dofetilide showed significantly reduced blockade of I(Kr), while in acidotic solution dofetilide showed significantly reduced blockade of I(Kr) and E-4031 showed a trend to reduced blockade. Neither drug significantly reduced total outward current in hyperkalemic or acidotic solutions. CONCLUSIONS: In these conditions, E-4031 and dofetilide demonstrate reduced blockade of I(Kr), resulting in loss of class III effect. Furthermore, the complete loss of blocking effect on total outward current during simulated ischemia suggests increases of other repolarizing currents also contribute to loss of class III effect.     

Differential Electrophysiologic Effects of Chronically Administered Amiodarone on Canine Purkinje Fibers versus Ventricular Muscle

BACKGROUND: Acute and chronic treatment with amiodarone has been reported to cause different electrocardiographic changes in patients. The cellular electrophysiologic effects of chronic administration (50 mg/kg/day orally for 6 weeks) and acute superfusion (5 μM in the tissue bath) of amiodarone were therefore studied in dog cardiac ventricular muscle and Purkinje fibers using conventional microelectrode techniques. METHODS AND RESULTS: During stimulation at 1 Hz, chronic amiodarone treatment lengthened the ventricular muscle action potential duration (APD) from 227.8 +/- 6.3 ms (n = 20) to 262.3 +/- 5.2 ms (n = 21; P <.01), but shortened that of Purkinje fibers from 337.6 +/- 9.2 (n = 21) to 308.3 +/- 7.1 (n = 19; P <.05). Acute superfusion of 5 μM amiodarone in cardiac tissue obtained from chronically treated dogs did not change ventricular muscle APD but shortened Purkinje fiber AP from 309.7 +/- 13.6 ms to 281.9 +/- 11.9 ms (n = 8; P <.05). Neither the chronic nor the acute amiodarone exposure prevented the APD shortening in ventricular muscle evoked by 10 μM pinacidil, suggesting that amiodarone does not interfere with the ATP-dependent potassium channels. The normal difference in APD between ventricular muscle and Purkinje fibers in untreated, control preparations was 110 ms but decreased to 46 ms in fibers obtained from dogs chronically treated with amiodarone and increased to 185 ms in fibers obtained from dogs chronically treated with amiodarone and increased to 185 ms in the presence of 30 μM sotalol, a class III antiarrhythmic drug used for comparison. Amiodarone (5 μM) applied directly abolished early afterdepolarizations (EADs) (induced by 1 μM dofetilide + 20 μM BaCl(2) + 2 mM CsCl) in 5 of 6 experiments and caused strong use-dependent V(max) block with relatively fast onset kinetics (rate constant = 1.23 +/- 0.13 AP(-1), n = 5) and offset (time constant = 364 +/- 62.5 ms, n = 5). After chronic amiodarone treatment, in contrast with acute sotalol application (30 μM), no reverse use-dependent effect was observed on the APD in Purkinje fibers. CONCLUSIONS: These results provide further evidence that amiodarone differs from other recognized class III antiarrhythmic drugs (ie, it is a mixed type agent with acute fast kinetic class I [type B] and a unique class III antiarrhythmic action characterized by decreased dispersion of APDs between ventricular muscle and Purkinje fibers). Amiodarone can abolish EADs unlike other class III agents that are usually associated to induction of EADs. These features might be responsible not only for the antiarrhythmic efficacy, but also for the relative safety (low incidence of torsade de pointes) of amiodarone in clinical settings.     

Effects of Verapamil on Ventricular Tachycardia Induced by Ouabain in Guinea Pigs

Calcium ions appear to play a central role in the development of ventricular arrhythmias associated with digitalis intoxication. Therefore, the effects of the calcium channel antagonist, verapamil, on ouabain-induced ventricular tachycardia were investigated. Ventricular tachycardia (three or more consecutive wide QRS complexes) was induced in guinea pigs by intravenous infusion of ouabain (1 microgram/min) and bursts of rapid ventricular stimulation. Of seven guinea pigs given the infusion of ouabain, all developed ventricular tachycardia at a dose of 82 +/- 17 micrograms/kg (mean +/- SD) and none developed heart block or asystole. Eight guinea pigs were treated with verapamil (2 micrograms/min for 30 minutes) prior to exposure to ouabain. Of those eight animals, only two developed ventricular tachycardia but six developed heart block or asystole at a significantly higher dose of ouabain (154 +/- 47 micrograms/kg). None of three control guinea pigs given an infusion of normal saline for 90 minutes developed ventricular tachycardia. These results show that pretreatment with verapamil inhibits ouabain-induced ventricular tachycardia in guinea pigs. Combined treatment with verapamil and ouabain is associated with a high incidence of heart block and asystole, which may limit the usefulness of verapamil.     

辛伐他汀对急性心肌梗死后兔心室肌细胞瞬间外向钾通道电流影响的实验研究

目的:探讨他汀类药物抗心律失常的细胞学离子机制。方法:将45只新西兰大耳白兔随机分为急性心肌梗死(AMI)模型组(心梗组)、辛伐他汀治疗组(他汀组)和假手术对照组(对照组),每组各15只。采用结扎兔冠状动脉左前降支的方法建立AMI模型。采用酶解的方法分离心室肌外膜单个心室肌细胞,采用电流-电压关系(I-V)全细胞膜片钳技术记录各组跨膜瞬间外向钾通道电流(Ito),同时检测各组血脂水平。结果:各组血脂水平无明显改变,差异无统计学意义(P>0.05)。I-V曲线Ito电流密度峰值( 60mV)时显示:对照组(n=15)为(17.41±3.13)pA/pF,心梗组(n=12)为(10.41±1.93)pA/pF,与对照组比较差异有统计学意义(P<0.01);他汀组(n=13)为(16.21±2.42)pA/pF,与心梗组比较差异有统计学意义(P<0.01)。Ito失活曲线显示:对照组(n=10)半数最大失活曲线(V1/2)为(-46.20±8.30)mV,心梗组(n=8)为(-55.20±9.30)mV,与对照组比较差异有统计学意义(P<0.01);他汀组(n=9)为(-48.50±9.20)mV,与心梗组比较差异有统计学意义(P<0.01)。Ito失活后再恢复曲线显示:2个脉冲间隔时间为60ms时,对照组(n=11)Ito恢复(66.5±13.2)%,心梗组(n=8)恢复仅(35.3±6.6)%,他汀组(n=10)恢复(58.5±12.5)%;脉冲间隔为180ms时,对照组Ito恢复(99.1±19.3)%,心梗组恢复(76.5±16.1)%,他汀组恢复(95.2±18.2)%;心梗组与对照组及他汀组比较差异均有统计学意义(P<0.01)。结论:AMI可导致梗死区心肌细胞Ito明显下降,形成电重构,通过辛伐他汀预处理可减轻Ito的异常变化,逆转电重构,而不依赖于降血脂效应,可能为他汀类药物抗心律失常的细胞学离子机制。     

Directional Variability of Stimulation Threshold Measurements in Isolated Guinea Pig Cardiomyocytes: Relationship with Orthogonal Sequential Defibrillating Pulses

BARDOU A.L., ET AL.: Directional Variability of Stimulation Threshold Measurements in Isolated Guinea Pig Cardiomyocytes: Relationship with Orthogonal Sequential Defibrillating Pulses. Reports on delivery of separated orthogonal pulses markedly improving cardiac defibrillation have suggested that the stimulation threshold of heart fibers varies in accordance with their orientation within the electric field. The present work was aimed at investigating the directional variability of stimulation thresholds in isolated guinea pig cardiomyocytes. This variability was measured in 48 single myocytes by rotating each one through a theta (θ) angle between two-fixed parallel electrodes 1.1 cm apart, thus making θ vary between the electric field and the myocyte axis. For θ= 0°, the mean longitudinal current stimulation threshold was 16.92 ± 4.20 mA (n = 48). When θ was increased by increments of 10° up to 90°, the stimulation threshold increased in an exponential way. For θ= 90°, the mean transverse stimulation threshold was 63.23 ± 13.30 mA. These results clearly demonstrate the dependence of isolated cardiomyocyte stimulation thresholds on their orientation within the electric field and may account for the improved efficacy of defibrillation previously observed after delivery of orthogonal pulses.     

Role of Electrophysiologic Testing in the Therapy of Ventricular Arrhythmias

The past decade has witnessed important advances in the understanding of the mechanism underlying ventricular arrhythmias. It has become clear that sustained ventricular arrhythmias can generally be reproduced with programmed ventricular stimulation in the clinical elec-trophysiology laboratory. False positive results may, however, occur with very vigorous stimulation techniques, particularly in patients without documented arrhythmias. False negative results are not infrequent in victims of cardiac arrest. Ability or inability to initiate ventricular tachycardia duringacute and chronic drug testing has predicted clinical failure or success, at least for conventional antiar-rhythmics. Patients with sustained ventric ular tachycardia and cardiac arrest occurring outside the peri-infarction period are those most likely to benefit from study. Conventional antiarrhythmic agents are successful in about one-third of patients with a high degree of concordance among these drugs. Amio-darone is frequently effective in patients with drug-refractory ventricular arrhythmias. However, its efficacy cannot be predicted by programmed stimulation. This is in striking contrast to Type 1A anti-arrhythmic agents.     

Reduction of Carnitine Content by Inhibition of Its Biosynthesis Results in Protection of Isolated Guinea Pig Hearts Against Hypoxic Damage

BACKGROUND: 3-(2,2,2-trimethylhydrazinium) propionate (THP or mildronate) is an inhibitor of carnitine biosynthesis. This study was carried out to determine whether feeding of guinea pigs with THP results in decreased myocardial-free carnitine content and, as a result, attenuates hypoxic damage in isolated and paced work-performing hearts. METHODS AND RESULTS: Guinea pigs were administered either distilled water of 100 mg THP/kg/day orally for 10 days. The treatment resulted in about a 50% decline in myocardial-free carnitine content, from 11.1 +/- 0.2 (n = 5) to 5.6 +/- 0.2 (n = 5) μM/g dry weight of the heart. The left ventricular contractile function of the hearts was measured during normoxic perfusion (PO(2) = 590 mmHg), hypoxic perfusion (PO(2) = 149 mmHg), and reperfusion (PO(2) = 590 mmHg). In both untreated and THP-treated groups, the rate of development of intraventricular pressure (+dP/dt) under normoxic perfusion was similar; however, +dP/dt declined to about 10% of the initial rate within 20 minutes of hypoxic perfusion. In the THP-treated group of hearts, the initial decline was slower than that of the untreated animal hearts. After 20 minutes of normoxic reperfusion following 60 minutes of hypoxic perfusion, the recovery of +dP/dt and -dP/dt was greater in the THP-treated group than in the untreated group. The elevation of end-diastolic pressure during hypoxia was completely reversed by normoxic reperfusion of the THP-treated group but not in the untreated group. Mitochondria isolated from hearts from the THP-treated group after normoxic reperfusion following hypoxic perfusion exhibited better respiratory function than those from untreated hearts. CONCLUSIONS: The data suggest that feeding guinea pigs with THP results in reduced myocardial-free carnitine content and attenuation of hypoxic and reperfusion injury in isolated hearts.     

Effect of Dofetilide and d-Sotalol on the ATP-Sensitive Potassium Channel of Rabbit Ventricular Myocytes

BACKGROUND: The ability of dofetilide and d-sotalol to maintain their class III action during ischemia is uncertain. We investigated the effect of these two drugs on the ATP-sensitive potassium channel (I(KATP)), which plays a major role in ischemia-induced action potential duration shortening. METHODS AND RESULTS: The activity of I(KATP) channels was studied in excised membrane patches of single ventricular myocytes, obtained by standard enzymatic dissociation techniques from New Zealand white rabbits. Dofetilide demonstrated a dose-dependent block of I(KATP) with an EC(50) of 51 +/- 1 μM in inside-out patches, Its ability to block the channel was substantially less when applied to the external membrane surface. d-Sotalol significantly blocked I(KATP) (42% reduction) at a concentration of 10 μM but not at 1 μM. As with dofetilide, its ability to block I(KATP) was reduced when applied externally. CONCLUSIONS: We conclude that dofetilide and d-sotalol block the ATP-sensitive potassium channel, but dofetilide does so only at concentrations much greater than those required for block of the delayed rectifier potassium channel. d-Sotalol in contrast shows modest blockade of I(KATP) at concentrations in the upper range of those seen during its clinical use.     

盐酸和氢氧化钠对豚鼠各段小肠平滑肌活动的影响

目的观察盐酸和氢氧化钠对豚鼠各段小肠平滑肌活动的影响。方法制备离体小肠平滑肌标本,放置于灌流浴槽中,观察其收缩活动的影响。结果与对照组相比,盐酸对十二指肠和空肠上段平滑肌自发收缩活动有增强效应(P<0.05),而对回肠下段平滑肌的自发收缩活动有抑制效应(P<0.05),氢氧化钠对空肠和回肠收缩活动均有抑制效应(P<0.05)。结论盐酸对豚鼠十二指肠和空肠平滑肌自发收缩活动有增强作用,而氢氧化钠对空肠和回肠的活动则有减弱作用。     

高压氧对庆大霉素致聋豚鼠影响的实验研究

目的 :观察高压氧对庆大霉素致聋豚鼠的影响。方法 :庆大霉素致耳聋的豚鼠 42只 ,随机分为 3组 ,每组 14只 :A .不治疗组 (对照组 ) ,B .即刻高压氧治疗组 (治疗组 1) ,C .延缓高压氧治疗组 (治疗组 2 )。通过测试听性脑干反应 (ABR)检测高压氧对耳聋的治疗效果。结果 :致聋豚鼠治疗前ABR阈 :对照组 5 5 .30± 6 .73,治疗组 1:5 0 .2 0± 7.32 ,治疗组 2 :47.6 0± 8.10 ;2个月后ABR阈分别为 :6 4.10± 6 .6 3,38.10± 9.70和 46 .5 0± 7.40。与治疗前相比较 ,治疗组 1听力有显著性改善 (P <0 .0 5 ) ,治疗组 2听力虽略有改善 ,但无统计学意义 (P >0 .0 5 ) ,而对照组听力进一步减退。结论 :对药物中毒性耳聋及早采取高压氧治疗有一定的疗效     

A Closed-Chest Pig Model of Sustained Ventricular Tachycardia

The goal of this study was to develop and explore a closed-chest animal model of sustained VT. Seven of 11 domestic pigs had successful induction of myocardiai infarction by injection of agarose gel microbeads into the left anterior descending coronary artery tbrougb an inflated balloon angioplasty catheter. Four of the first five pigs died and seem to represent a "learning experience." During a 3- to 50-day follow-up period, each pig underwent 1 -3 electropbysiological studies. Sustained, monomorpbic VT was induced 1–4 times in 5 of the 7 pigs (a total of 19 episodes), was reproducible during the same study in all pigs, and could be repetitively induced during successive studies in some. Ventricular fibrillation was induced less frequently (nine episodes) and was successfully terminated by DC shock in eight episodes. We conclude tbat a closed-cbest pig model of VT is feasible and is associated witb a relatively bigb induction rate of sustained, monomorpbic, and reproducible VT and a relatively low mortality rate.     

Synthesis of Factor VIII Antigen by Cultured Guinea Pig Megakaryocytes

Immunoprecipitates containing guinea pig Factor VIII antigen were prepared from guinea pig plasma with a cross-reacting rabbit anti-human Factor VIII. Monospecific antisera to guinea pig Factor VIII antigen were produced in rabbits by using these washed immunoprecipitates as immunogens. The resulting antisera to guinea pig Factor VIII antigen detected Factor VIII antigen in guinea pig plasma and inhibited the von Willebrand factor activity in guinea pig plasma. This antibody also detected Factor VIII antigen in a solubilized protein mixture prepared from isolated cultured guinea pig megakaryocytes. Cultured guinea pig megakaryocytes were labeled with radio-active leucine. By radioautography, 96.2% of the radio-activity was present in megakaryocytes. The radio-active Factor VIII antigen present in the solubilized cell protein mixture was isolated by immunoprecipitation and characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The results demonstrate that cultured guinea pig megakaryocytes synthesize Factor VIII antigen which contains the same polypeptide subunit (mol wt 200,000) present in guinea pig plasma Factor VIII antigen.     

母牛分枝杆菌菌苗对哮喘豚鼠肺组织嗜酸粒细胞凋亡及Fas蛋白表达的影响

目的 :研究母牛分枝杆菌菌苗对哮喘豚鼠肺组织嗜酸粒细胞凋亡及 Fas蛋白表达的影响。方法 :30只豚鼠随机分为生理盐水组、哮喘组及母牛分枝杆菌菌苗组 ,用 TUNEL法检测肺组织嗜酸粒细胞凋亡 ,免疫组化法检测肺组织 Fas蛋白的表达。结果 :母牛分枝杆菌菌苗组豚鼠肺组织嗜酸粒细胞凋亡指数 (2 3.8± 5 .4 ) %显著高于哮喘组 (4.6±0 .7) % (P<0 .0 1) ;肺组织 Fas表达 (OD值 ) (0 .2 0 2± 0 .0 13)显著高于哮喘组 (0 .0 5 1± 0 .0 2 5 ) (P<0 .0 1)。结论 :母牛分枝杆菌菌苗通过上调 Fas蛋白在哮喘豚鼠肺组织的表达而诱导肺组织嗜酸粒细胞凋亡     

彩色多普勒超声心动图对孤立性心室致密不全的诊断价值

目的 :探讨孤立性心室致密不全 (IVNC)的临床及超声心动图特点 ,评价超声心动图技术对 IVNC的诊断价值。方法 :对 9例 IVNC患者应用彩色多普勒超声心动图进行多切面探查。显示致密不全累及的节段。测量左室射血分数(L VEF)、致密不全内膜 (T1)与致密外膜厚度 (T2 )比值 (T1/T2 )。探查肌小梁间隙内血流以及有无血栓形成。结果 :1.超声心动图特点 :受累节段的室壁分为两层 ,即薄的致密外膜层和厚的致密不全内膜层 ,内、外层厚度比 2 .9± 0 .7;彩色多普勒显示 ,小梁间隙血液与左心腔相通 ;小梁间隙内未探及附壁血栓 ;8例患者 L VEF降低 43 %± 8% ;4例合并二尖瓣返流 ;致密不全共累及 3 9个节段 ,74.4% (2 9/3 9)位于心尖段、侧壁、下壁及后壁的中段 ;2 .临床特点 :左心功能不全者 7例 ;心电图异常者 8例 ;临床无栓塞事件发生。结论 :IVNC具有典型的超声心动图特征 ,彩色多普勒超声心动图技术具有重要诊断价值