心肌细胞膜血管紧张素Ⅱ受体对膜离子通道的调节作用

应用膜片钳技术，研究了血管紧张素Ⅱ受体对心肌细胞离子通道的调节作用。结果显示：（１）ＡｎｇⅡ延长Ｌ型钙通道电流的激活和失活时间，其作用可被Ｌｏｓａｒｔａｎ阻滞，被Ｈ－７抵消，被ＴＰＡ加强，提示其作用经ＡＴ１受体，由Ｇ蛋白介导，激活蛋白激酶增加，延长Ｌ型钙通病电流；（２）ＡｍｇⅡ抑制延迟整流性钾通道电流，钾通道外向尾电流，缩短钾通道外向尾电流的快，慢失活时间，该作用也能被Ｌｏｓａｒｔａｎ阻滞，提示其     

第一种非肽类特异性血管紧张素Ⅱ受体拮抗剂—Losartan的发现

血管紧张素转换酶抑制剂(ACEI)如卡托普利(captopril)、依那普利(enalapril)在治疗高血压、心力衰竭方面已取得成功。这类药物的疗效归功于抑制肾素血管紧张素系统(RAS)的活性。由于血管紧张素转换酶(ACE)除了作用于血管紧张素Ⅰ以外,对其它方面如缓激肽、P物质也有影响,所以就RAS而言,选择性血管紧张素Ⅱ(ATⅠ)受体拮抗剂较ACEI更能获得最大的抑制效果。关于非ACE途径产生的AT I,以及循环RAS及局部组织RAS的情形已有报道。理论上证实,在受体水平依据活性肽与受体的相互作用机制,AT I受体拮抗剂将特异性     

血管紧张素Ⅱ受体及其受体拮抗剂研究进展

血管紧张素Ⅱ（AngⅡ）是肾素-血管紧张素系统（RAS）中最为重要的活性激素，它在高血压的病理生理中起着重要的作用。AngⅡ的作用通过细胞表面的AngⅡ受体介导，根据与不同受体拮抗剂的选择性可将其受体分为两个亚型：AT1受体和AT2受体。已知的AngⅡ的生理作用是由AT1受体介导的AT2受体的功能尚不清楚，在临床上主要有两种抑制RAS活性的药物；一是血管紧张素转化酶抑制剂（ACEI），它抑制AngⅡ的生成；二是AT1受体拮抗剂，它阻断AngⅡ相应受体的生理学作用。AT1受体拮抗剂的潜在临床实用性正在得到深入研究。     

血管紧张素Ⅱ受体拮抗剂与高血压

血管紧张素Ⅱ受体拮抗剂降压疗效与其它一线降压药相同但毒副作用明显较低,是目前较理想的降压药。本文瓣近年有关血管紧张素Ⅱ受体及其拮抗剂与高血压的研究进行了综述。     

血管紧张素Ⅱ受体拮抗剂防治心力衰竭的研究进展

在心力衰竭（HF）发生发展的整个病理过程中肾素-血管紧张素-醛固酮系统（RASS）起了极其主要的作用。尽管血管紧张素转换酶抑制剂（ACEI）明显改善了慢性HF的预后，但病情仍在继续发展。血管紧张素Ⅱ（AngⅡ）受体拮抗剂的问世针对防治心脏重构，改善HF预后的一些临床研究已被逐步得到了证实，肯定了AngⅡ受体拮抗剂治疗HF独特的生物药理效应和临床地位。     

常用血管紧张素Ⅱ受体拮抗剂研究进展

血管紧张素Ⅱ受体拮抗剂与血管紧张素Ⅱ1型受体选择性结合,从而阻止多途径源性的血管紧张素Ⅱ生成,在高血压、心肌肥厚、心力衰竭、糖尿病肾病等治疗中发挥重要作用.现综述了该类药物在药物代谢、临床应用、禁忌证等方面的研究进展.     

血管紧张素Ⅱ受体拮抗剂的临床研究进展

血管紧张素Ⅱ受体拮抗剂的临床研究进展陈鲁原林曙光由于肾素血管紧张素系统（ＲＡＳ）在血压调节机制中起着极为重要的作用，目前高血压的治疗正日益集中在抑制血管紧张素Ⅱ（ＡｎｇⅡ）水平上。一系列大规模临床试验表明，血管紧张素转换酶（ＡＣＥ）抑制剂在治疗高血...     

血管紧张素Ⅱ受体拮抗剂在糖尿病肾病中的应用

介绍了血管紧张素Ⅱ受体及其拮抗剂的分型和作用,并比较了血管紧张素Ⅱ受体拮抗剂和血管紧张素转换酶抑制剂在糖尿病肾病中的作用,前者显示了较好的应用前景。     

Two types of calcium channels in guinea pig ventricular myocytes.

In cardiac muscle, Ca2+ plays a key role in regulation of numerous processes, including generation of the action potential and development of tension. The entry of Ca2+ into the cell is regulated primarily by voltage-gated channels in the membrane. Until recently, it was felt that only one type of Ca2+ channel existed in cardiac ventricular muscle. Experiments reported here suggest that in isolated guinea pig ventricular myocytes, there are two distinct types of Ca2+ channels with markedly different activation thresholds, inactivation kinetics, and sensitivities to inorganic and organic Ca2+ channel blockers. The channels were also distinguished based on their response to increased frequency of clamping such that the current through the low-threshold channel decreased while that through the high-threshold channel increased. In a few cells, the current through both channels was enhanced by isoproterenol, a beta-adrenergic agonist, but only the high-threshold channel was enhanced by the Ca2+-channel agonist Bay K 8644. Thus, isolated guinea pig ventricular myocytes appear to have two types of Ca2+ channels distinguished by various criteria.     

卡维地洛对豚鼠心室肌细胞的电生理作用

目的:观察卡维地洛对豚鼠心室肌细胞膜离子流及跨膜动作电位的影响,探讨卡维地洛对心室肌细胞的直接电生理作用.方法:①应用膜片钳全细胞记录技术记录单个豚鼠心室肌细胞膜L型钙内流(ICa-L)、内向整流性钾流(IJ1)、延迟整流性钾流(IK)和快钠内流(INa),观察不同浓度的卡维地洛对各离子流的影响.②用标觋准微电极技术记录豚鼠右室乳头肌细胞动作电位,观察不同浓度卡维地洛对动作电位各参数的影响.结果:①卡维地洛浓度依赖性地抑制ICa-L、INa,半数抑制浓度(IC50)分别为3.18,0.16 μmol/L.②卡维地洛25μmol/L对IK1最大内向和外向电流差异无统计学意义(n=5,P＞0.05),但使其整流范围由-20～ 40 mV增大至-20～ 80 mV.③卡维地洛0.3μmol/L以上即可浓度依赖性抑制IK尾电流(IK.tail),且对-10 mV钳制电压下IK.tail的抑制作用明显大于对 50 mV下的抑制,在高浓度还抑制缓慢激活型IK(IKs),IC50为12.43μmol/L.④卡维地洛呈反转频率依赖性延长动作电位时程(APD90),还降低动作电位幅度(APA)和0相最大去极化速率(Vmax).结论:卡维地洛低浓度下即可抑制心肌细胞INa、快速激活相IK,高浓度下抑制ICa-L、IKs,还降低Vmax、APA,呈反转频率依赖性延长APD90.     

Diltiazem facilitates inactivation of single L-type calcium channels in guinea pig ventricular myocytes

Diltiazem is a benzothiazepine Ca2+ channel blocker used clinically for its antihypertensive and antiarrhythmic effects. We studied the mechanism of diltiazem blockade by recording L-type Ca2+ channel currents from cell-attached patches in isolated guinea pig ventricular myocytes using Ba2+ as the charge carrier. With diltiazem (200 microM) in the superfusate, multichannel currents showed a use-dependent decline in amplitude reflecting reductions in the numbers of superpositions of channel openings. Analysis of single-channel currents revealed that both open and closed times were little affected by diltiazem (50 and 100 microM). However, the rate of decay of the averaged current during 150-ms depolarization steps was significantly accelerated and the open state probability in current containing-sweeps was significantly decreased by diltiazem, suggesting that the drug accelerates transition from the activated state to the inactivated state. The effect of diltiazem on the slow gating process was studied by repetitively applying 500-1000 step pulses at selected holding potentials. Decreased channel availability by diltiazem was reflected by the increasing number of blank sweeps per run at depolarized holding potentials. These results suggest that diltiazem reduces Ca2+ influx by accelerating inactivation during action potentials, and that the use-dependent blockade is due to increases in the number of channels in a sustained closed state.     

二十二碳六烯酸对心室肌细胞离子通道的影响

近年来,n-3多不饱和脂肪酸(n-3PUFAs)对心血管的有益作用已受到广泛重视.大量研究表明n-3PUFAs具有抗心律失常作用,能降低冠心病的猝死率及心肌梗死后恶性心律失常的发生率[1].基于这些研究结果,在心血管疾病的一级和二级预防中,美国和欧洲等心脏病学会推荐每日摄入小剂量n-3PUFAs[2].目前,n-3PUFAs抗心律失常的机制仍不完全清楚.n-3PUFAs主要包括二十二碳六烯酸(DHA)和二十碳五烯酸(EPA).本文通过膜片钳技术探讨DHA对大鼠心室肌细胞静息电位(RP)、动作电位时限(APD)、延迟整流性钾通道电流(IK)及内向整流性钾通道电流( IKl)的影响,阐述DHA抗心律失常的可能机制. 1.材料和溶液组成:Axopatch 700B膜片钳放大器、Digi-Data 1322型数/模(或模/数)转换器、pClamp 9.0脉冲发放和数据采集软件(美国Axon Instruments公司).DHA(美国Sigma公司)以无水乙醇配制成50 mmol/L的母液,分装避光保存于-80℃备用.使用时无水乙醇的终浓度＜0.4％,以避免无水乙醇对离子通道的影响.牛血清白蛋白(BSA,美国Sigma公司)配制成2 mg/ml,4℃保存.     

模拟缺血对心室肌细胞钙内流和钾外流的影响

目的 观察模拟缺血对心室肌细胞L—型钙通道和ATP敏感钾通道的影响。方法 实验用胶原配药解法急性分离豚鼠心室肌细胞，利用全细胞膜片钳的方法记录心室肌细胞的L—型钙电流(Ica.L)和ATP敏感钾电流(IKATP)。采用低氧、无糖、高钾、高乳酸和酸中毒综合方式模拟缺血灌流，造成细胞的模拟缺血。结果 模拟缺血时，Ica.L明显受到抑制，IKATP增加，后一效应能被优降糖所阻断。结论 模拟缺血时Ica.L明显受到抑制，IKATP增加，可能是导致心室肌细胞动作电位时程缩短的主要因素之一。     

Stereoselective block of cardiac sodium channels by RAC109 in single guinea pig ventricular myocytes

The effects of the optical stereoisomers of the local anesthetic RAC109 (RAC109-I and RAC109-II) on sodium current in isolated guinea pig ventricular myocytes were investigated by use of the whole-cell variation of the patch-clamp technique. RAC109-I and RAC109-II produced similar levels of tonic block, but RAC109-I produced a significantly larger use-dependent block on repetitive pulsing to potentials positive to -60 mV. Definition of the time courses of block development at -20 mV and recovery at -140 and -160 mV indicated that RAC109-I had a higher affinity for activated and inactivated channels and dissociated more slowly at hyperpolarized potentials compared with RAC109-II. Removal of fast inactivation by alpha-chymotrypsin intensified tonic block but did not reduce use-dependent block by RAC109-I; this finding suggests that channel inactivation is not necessary for use-dependent block. The guarded-receptor model was used to calculate apparent rate constants of drug binding and unbinding. According to the model, RAC109-I and RAC109-II have significantly different unbinding rate constants for channels when they exist predominantly in rested, activated, or inactivated states, as well as significantly different binding rate constants when channels are activated. However, the apparent rates of drug binding to closed (rested and inactivated) channels are not significantly different for the two isomers; this finding indicates that drug binding to closed channels is not markedly stereospecific, in contrast to unbinding. The effects of RAC109 stereoisomers on cardiac sodium channels were also qualitatively similar to those previously reported in nerve; these findings suggest that the binding sites for local anesthetics in both tissue types have a similar structural topography.     

Quinidine delays IK activation in guinea pig ventricular myocytes

A major action of the antiarrhythmic agent quinidine is prolongation of cardiac repolarization. In these experiments, the time-dependent effects of quinidine on the delayed rectifier potassium current, IK, a current contributing to cardiac repolarization, were investigated in acutely disaggregated guinea pig ventricular myocytes using the whole-cell recording configuration of the patch-clamp method. The effect of quinidine on IK was dependent on the duration of depolarization. After long (2,000 msec) pulses, IK was reduced by 30 +/- 27% (SD; n = 8, paired) by 10 microM quinidine; in contrast, after short (100 msec) pulses, the drug decreased IK 65 +/- 35% (p less than 0.05). This effect was found both in paired experiments as well as when quinidine-pretreated cells were compared to non-pretreated cells. Quinidine significantly delayed IK activation (9 +/- 20 msec at baseline vs. 44 +/- 25 msec in drug, p less than 0.05), but did not alter the subsequent time course of activation (time constant 659 +/- 118 msec). These findings are consistent with the hypothesis that quinidine promotes occupancy of a channel state from which opening does not occur.     

Amantadine-induced afterpotentials and automaticity in guinea pig ventricular myocytes

The ionic mechanisms of amantadine-induced changes in membrane potential and automatic activity in guinea pig ventricular myocytes were studied using the suction-pipette whole-cell clamp method. While 25-100 microM amantadine decreased the action potential amplitude and duration, 200 and 400 microM amantadine lengthened the action potential duration and decreased the maximum diastolic potential with an appearance of diastolic depolarization and automaticity. In the presence of 25-100 microM amantadine, the preparations developed an afterpotential due to incomplete repolarization and a delayed afterdepolarization that eventually brought about triggered automaticity. The former type of afterpotential was abolished by tetrodotoxin (TTX) and the latter by Co2+. Spontaneous activity from the diastolic depolarization was also abolished by Co2+ but not by Cs+. Amantadine suppressed the calcium current to as much as half of the control at the concentrations used (25-200 microM). The drug also produced a depression of the inward rectifier K+ current. The outward current showing time-dependent decay was activated at the plateau voltages by concentrations lower than 100 microM, whereas the delayed outward K+ current was depressed by the drug in a concentration-dependent manner at more positive potentials. Amantadine activated the TTX-sensitive and TTX-insensitive inward currents on repolarization from depolarized states, without producing the transient inward current. These results indicate that the amantadine-induced diastolic depolarization and afterpotentials are caused by changes in multiple ionic currents and that, therefore, the drug can be used as a unique model for the study of arrhythmogenesis.     

牛磺酸对低氧条件下豚鼠心室肌细胞内向整流钾电流的影响

目的:研究牛磺酸对低氧条件下豚鼠心室肌细胞内向整流钾电流(Ik1)的影响。方法:酶解法分离单个豚鼠心室肌细胞和建立离体低氧模型,采用全细胞膜片钳记录技术记录牛磺酸对急性低氧条件下豚鼠心室肌细胞Ik1的作用。结果:在钳制电压-40 mV下,给予20 mmol/L牛磺酸使Ik1的电流峰值降低,抑制率(45.61±10.70)%;洗脱后,Ik1能够部分恢复(P<0.05)。牛磺酸影响了Ik1的电流-电压曲线。结论:牛磺酸可明显阻滞低氧条件下豚鼠心室肌细胞膜上Ik1电流,这可能是其抗心律失常作用的电生理机制之一。