家兔急性缺血早期心室肌细胞跨膜电位的变化及迷走神经的保护作用

以在体家兔的心脏为对象,应用浮置微电极技术研究了急性缺血早期心室肌细胞跨膜电位的变化及迷走神经的保护作用。 冠状动脉的一个分支阻断后 1—5min,静息电位(RP)、动作电位振幅(APA)和 0相最大上升速率(dv/dt)_(max)均减小(P<0.01)。动作电位时程APD_(30)、APD_(50)和APD_(90)均缩短(P<0.01)。反映 2相平台时程的 APD_(30)和 APD_(50)缩短较总时程 APD_(90)的缩短更明显。 在自然心率的条件下,左颈迷走神经电刺激,可使急性缺血的心肌电位的变化有所恢复:RP、APA、(dv/dt)_(max)均增加,APD_(30)、APD_(50)、APD_(90)延长(P_均<0.01)。刺激迷走神经时缺血的心室肌细胞跨膜电位有所恢复,对防止缺血早期的室性心律失常可能具有重要作用。     

孕酮对豚鼠心室肌细胞动作电位的影响

目的：观察孕酮(pfogesterone)对心室肌细胞动作电位的影响。方法：采用玻璃微电极技术,引导离体豚鼠心室乳头肌细胞动作电位,观察孕酮不同浓度及作用时间对心室肌细胞动作电位及有效不应期的影响。结果：①较高浓度的孕酮使心室肌细胞动作电位零期最大除极速率(Vmax)和动作电位幅度(APA)降低,使心室肌细胞有效不应期(ERP)延长;②较高浓度孕酮使心室肌细胞动作电位时程APD20缩短;使动作电位时程APD90、APD延长。结论：孕酮具有抑制心室肌细胞Na^ 通道、K^ 通道和Ca^2 通道的作用。     

镁对缺血性心肌电变化的保护作用

本工作研究了镁对模拟缺血条件（用低氧分压、无糖、高钾及高乳酸台氏液浸浴心肌）下的离体豚鼠心室肌细胞跨膜电位（TMP）和机能不应期（FRP）变化,以及在体兔心急性心肌缺血时FRP变化的影响。高镁（[M^2 ].8mmol/L）使模拟缺血豚鼠心室肌细胞静息电位（RP）、动作电位振幅（APA）及动作电位0期最大上升速度（Vmax)相对增大,动作电位时程（APD）相对延长,镁对缺血心肌FRP的变化具有双重作用,既可使过分延长的不应期相对缩短,减轻复极后不应性（PRP）;又可使缩短的不应期相对延长,从而减轻了不应期离散程度,镁的上述作用对改善缺血心肌的兴奋性,传导性,减少折返激动的发生具有重要意义。     

达乌尔黄鼠心肌细胞膜电位的耐寒性

用胞内微电极记录达乌尔黄鼠心室乳头肌细胞膜电位,研究它的耐寒性并附带观察季节及冬眠的影响。76％和55％的心肌标本分别在0℃至—5℃之间可诱发动作电位。3例心肌超冷至-5℃时静息电位(RP)66.6mV,为35℃时的80％,动作电位幅值(APA)60.4mV,为66％,但复温后可完全恢复。RP与APA比最大去极化率(dV/dt_(max))和动作电位时程(ADP)对寒冷有较大的抵抗力。季节对心肌膜电位活动有明显的影响,冬季深眠黄鼠的心肌RP和APA在0℃中显著高于冬季活跃组,提示深眠黄鼠的心肌有较大的耐寒性。这些结果说明冬眠型哺乳动物的心肌细胞膜电位比非冬眠型的有显著较大耐寒性。     

镉对大鼠心室肌细胞动作及L-型钙电流的影响

目的:探讨镉(Cd)对大鼠心室肌细胞动作电位(AP)及L-型钙电流(ICa-L)影响。方法:用常规微电极和全细胞膜片钳技术记录心肌细胞动作电位和ICa-L。结果:①不同浓度的CdCl2可降低大鼠心肌细胞动作电位幅值(APA),缩短复极化时程(APD)。②不同浓度的CdCl2明显抑制大鼠心室肌细胞钙通道电流。结论:CdCl2抑制大鼠心室肌细胞动作电位和ICa-L,可能是Cd对心肌毒性的重要机制之一。     

银杏苦内酯B对缺血豚鼠心室肌动作电位、L-型钙电流和延迟整流钾电流的作用

目的:研究银杏苦内酯B对正常和缺血心室肌细胞动作电位(action potential,AP),L-型钙电流(L-type calcium current,ICa-L)、延迟整流钾电流(Delayed Rectifier Currennt,IK)的影响.方法:用常规细胞内微电极方法记录豚鼠心室肌细胞动作电位,用全细胞膜片钳技术记录游离心室肌细胞离子流.结果:①在生理条件下,银杏苦内酯B可缩短心室肌细胞动作电位时程 (action potential duration,APD),但对AP其他参数无影响,银杏苦内酯B可增大IK,呈浓度依赖性,但对ICa-L无显著作用;②在缺血条件下,APD50、APD90明显缩短,RP、APA减小,Vmax减慢,而银杏苦内酯B则可延缓和减轻缺血所引起上述参数的变化;3.在缺血条件下,IK和ICa-L均受到抑制,但加入银杏苦内酯B后可逆转缺血所造成这两种离子流的减小.结论:银杏苦内酯B可对抗心肌缺血所引起的心肌电生理的变化,提示银杏苦内酯B可预防心律失常的发生.     

Ⅰ-磷酸鞘氨醇对豚鼠心室肌动作电位和收缩力的影响

目的研究1-磷酸鞘氨醇(SIP)对豚鼠心室肌动作电位(AP)和心肌收缩力(CF)的影响.方法实验采用标准玻璃微电极细胞内记录技术记录心室肌细胞动作电位(AP)肌力换能器记录心肌收缩力(CF).结果①应用0.1μmol/LSlP后心室肌动作电位幅度(APA)和时程(APD)与应用SIP前比较差异无显著性,而应用1.0μmol/LSlP,10μmol/L SIP后心室肌动作电位的幅度(APA)与应用SIP前比较明显降低而动作电位的时程(APD)与应用SIP前比较明显延长(P＜0.01).②应用1.0μmol/L SIP和10μmol/LSIP后心室肌的CF与给药前相比明显增强(P＜0.01),应用0.1μmol/LSlP后心室肌的CF与给药前比较差异无显著性(P＞0.05).而加入SIP特异性G蛋白耦联内皮细胞分化基因(EDG)受体阻断剂苏拉明后,SIP的上述作用与给药前比较差异无显著性(P＞0.05).结论SIP可以降低心室肌动作电位幅值延长动作电位时程,增加心室肌收缩力,并且是通过其特异性的G蛋白耦联内皮细胞分化基因(EDG)受体介导而产生这些作用,有一定的剂量依赖性.     

低镁和缺镁对离体豚鼠右心室肌单细胞动作电位的效应

取豚鼠右心室肌,在改良 Krebs 溶液灌注下,用微电极记录动作电位(AP)12只豚鼠72次心肌单细胞 AP 有关参数的平均值为:静息电位(RP)-76±9mV;动作电位振幅(APA)107±7mV;动作电位时程(APD)_(_30mv)为254±123ms;APD_(100)为312±133ms。当灌注液中镁离子浓度减低到0.6mol/L 时,72次 AP 的 APD_(_30mv)和APD_(100)分別为对照值的80.7%和83%;在无镁溶液中,改变更为显著,分别为对照值的70.9%和76.7%;RP 和 APA 则变化均不大。实验提示:低镁可使 APD 缩短,从而可能影响体表心电图 T 波的第3位相;此外,APD 的缩短意味着不应期相对缩短,这或许是低镁症时出现室性早搏的因素。     

在生理温度下降钙素基因相关肽对豚鼠心房肌复极过程的影响

实验应用常规微电极方法研究了在生理温度下 (36 5± 0 5℃ )降钙素基因相关肽 (calcitoningene relatedpeptide ,CGRP)对豚鼠心房肌细胞复极过程的影响及其与钾电流的关系。结果表明 :(1)CGRP(16nmol/L)可拮抗由钾通道阻断剂BaCl2 、4 AP引起的动作电位时间延长。 (2 )CGRP(16nmol/L)能够增加细胞外高钾 (18 5mmol/L)条件下心房肌慢反应动作电位的APA和Vmax,并缩短传导时间。 (3)CGRP(16nmol/L)能减弱甚至消除因并用CsCl (5mmol/L)和无钾灌流液诱发的触发活动。 (4)CGRP对动作电位复极过程的作用因温度条件而异。在生理温度下 ,CGRP(5、16和 5 0nmol/L)能够使动作电位平台抬高 ,缩短动作电位复极化 2 0 %、5 0 %和 90 %时程。其中 ,对动作电位复极化 2 0 %、5 0 %时程的作用呈剂量依赖性。而在室温下 (2 5 5± 2 1℃ ) ,CGRP使动作电位复极化 2 0 %、5 0 %和90 %时程延长。上述结果提示 ,CGRP对心房肌细胞具有多重电生理效应 ,其中生理温度下CGRP对钾电流的促进作用在动作电位的改变中占重要地位 ,今后有必要进一步研究CGRP对各种钾通道的作用     

镉对豚鼠乳头肌动作电位的影响

目的:研究氯化镉(CdCl2)对正常豚鼠心室乳头肌细胞动作电位(AP)的影响。方法:用常规细胞内微电极方法记录乳头肌细胞AP。结果:在生理条件下,CdCl2可使APo期振幅(APA)和最大除极速率(Vmax)降低,动作电位时程(APD)缩短,且具有剂量依赖性。结论:CdCl2可使心室肌AP的APA、Vmax、APD发生改变,提示CdCl2有抑制Na 、Ca2 内流和激活K 外流作用。     

铬对大鼠心电图及心肌细胞的电生理影响

应用心电图及细胞内微电极技术观察铬对心肌电生理的影响。大鼠腹腔内注射铬,９周后心电图显示各剂量组ＱＴ间期均缩短,细胞内微电极检查显示动作电位时程（ＡＰＤ５０、ＡＰＤ９０）于２周后随剂量增加而逐渐缩短,０．４ｍｇ组显著缩短,９周后各剂量组ＡＰＤ５０、ＡＰＤ９０均缩短。心率、静息电位（ＲＰ）与动作电位（ＡＰＡ）幅度及动作电位最大上升速率（Ｖｍａｘ）无变化。铬影响了心肌复极引起ＱＴ间期缩短,而ＡＰＤ５０、ＡＰＤ９０缩短可能是铬影响了钙内流及钾外流的结果。     

神经递质对豚鼠左心室流出道自律细胞电活动的影响

为研究左心室流出道慢反应自律细胞的神经支配和受体分布,本实验采用标准玻璃微电极细胞内记录技术,分别观测了肾上腺素能和胆碱能受体激动剂及相应的受体拮抗剂对离体豚鼠左心室流出道组织自发慢反应电位的影响。观测指标有：最大舒张电位（maximal diastolic potential,MDP）、动作电位幅度（amplitude of action potential,APA）、0相最大去极速度（maximal rate of depolarization,Vmax）、4相自动去极速度（velocity of diastolic depolarization,VDD）、复极50％时间（50％of duration of action potential,APD50）和90％时间（90％ of duration of action potential,APD50）以及自发放电频率（rate of pacemaker firing,RPF）。结果表明：（1）100μmol／L异丙肾上腺素（isoprenaline,Iso）可使RPF和VDD显著加快（P〈0．01）,MDP绝对值和APA显著增大（P〈0．05,P〈0．01）,Vmax加快（P〈0．05）,APD50缩短（P〈0．01）,这些变化均可被5μmol／L心得安拮抗;（2）100μmol／L肾上腺素（epinephrine,E）可使RPF和VDD加快（P＜0．01,P〈0．05）,APA显著增大（P〈0．001）,Vmax加快（P〈0．05）,APD50和APD90缩短（P＜0．05）;（3）100μmol／L去甲肾上腺素（norepinephrine,NE）可使VDD和RPF加快（P＜0．05）,APA显著增大（P〈0．05）,Vmax明显加快（P〈0．05）,APD50缩短（P〈0．05）,这些变化可被100μmol／L酚妥拉明拮抗;（4）10μmol／L ACh可使VDD和RPF减慢（P〈0．05）,APA显著减小（P〈0．01）,APD50缩短（P〈0．05）;ACh对APD50的缩短效应可被10μmol／L阿托品拮抗（P〈0．05）。结果提示：左心室流出道自律细胞膜上可能存在α-肾上腺素能受体（α-adrenergic receptor,α-AR、β-肾上腺素能受体（β-adrenergic receptor,β-AR）以及M型胆碱能受体（muscarinic receptor,MR）,其自律性电活动可能也接受心交感神经和心迷走神经调控。     

Electrophysiological changes induced by lysophosphatidylcholine, an ischaemic phospholipid catabolite, in rabbit atrial and ventricular cardiac cells.

The effects of palmitoyl-lysophosphatidylcholine (LPC) were studied on the cellular electrical activity of rabbit heart preparations. LPC (100 mumol/l) caused a considerable enhancement of the automaticity of the SA nodal and Purkinje fibers and frequently induced irregular firing in both supraventricular (SA node, atrium, AV junction) and ventricular (Purkinje fibers, papillary muscle) myocardial regions. The 'automatotropic' and arrhythmogenic effects of LPC were accompanied by a lengthening of the atrioventricular conduction time. In ventricular muscle fibers LPC (100 mumol/l) decreased the resting potential (RP), the maximum rate of depolarization (Vmax) and the amplitude (APA) and duration (APD) of the action potential, and often evoked action potentials of 'slow response' type. In atrial muscle cells, 100 mumol/l LPC was capable of inducing hyperpolarization, with concomitant increases in RP, Vmax, APA and APD; higher concentrations (300 and 600 mumol/l) of LPC resulted in decreases in RP, Vmax, APA and APD, i.e. phenomena similar to those observed with 100 mumol/l LPC in the ventricular myocardium. The results seem to support the assumption that lysolipids accumulating in the ischaemic myocardium may play a pathogenetic role in the development of both supraventricular and ventricular dysrhythmias accompanying coronary artery occlusion.     

Functional alterations after cardiac sodium-calcium exchanger overexpression in heart failure

The sodium-calcium exchanger (NCX) is discussed as one of the key proteins involved in heart failure. However, the causal role and the extent to which NCX contributes to contractile dysfunction during heart failure are poorly understood. NCX overexpression was induced by infection with an adenovirus coding for NCX, which coexpressed green fluorescence protein (GFP) (AdNCX) by ex vivo gene transfer to nonfailing and failing rabbit cardiomyocytes. Myocardial gene transfer in rabbits in vivo was achieved by adenoviral delivery via aortic cross-clamping. Peak cell shortening of cardiomyocytes was determined photo-optically. Hemodynamic parameters in vivo were determined by echocardiography (fractional shortening) and tip catheter [maximal first derivative of left ventricular (LV) pressure (dP/dt(max)); maximal negative derivative of LV pressure (-dP/dt(max))]. Peak cell shortening was depressed after NCX gene delivery in isolated nonfailing and in failing cardiomyocytes. In nonfailing rabbits in vivo, basal systolic contractility (fractional shortening and dP/dt(max)) and maximum rate of LV relaxation (-dP/dt(max)) in vivo were largely unaffected after NCX overexpression. However, during heart failure, long-term NCX overexpression over 2 wk significantly improved fractional shortening and dP/dt(max) compared with AdGFP-infected rabbits, both without inotropic stimulation and after beta-adrenergic stimulation with isoproterenol. -dP/dt(max) was also improved after NCX overexpression in the failing rabbits group. These results indicate that short-term effects of NCX overexpression impair contractility of isolated failing and nonfailing rabbit cardiomyocytes. NCX overexpression over 2 wk in vivo does not seem to affect myocardial contractility in nonfailing rabbits. Interestingly, in vivo overexpression of NCX decreased the progression of systolic and diastolic contractile dysfunction and improved beta-adrenoceptor-mediated contractile reserve in heart failure in rabbits in vivo.     

An analysis of the direct effect of chloridazepoxide on mammalian cardiac tissues and crayfish and squid giant axons: possible basis of antiarrhythmic activity.

Chlordiazepoxide has been found to be antiarrhythmic $\text{in vivo}$. The purpose of the present investigation is to identify the mechanism(s) of such antiarrhythmic activity. In canine heart, chlordiazepoxide effectively depressed the enhanced repetitive discharges in subendocardial Purkinje fibers surviving acute myocardial infarction. Chlordiazepoxide altered the action potential characteristics of Purkinje fiber by shortening the APD₅₀, APD₁₀₀ and effective refractory period with little effect on the resting membrane potential. The maximal rate of upstroke (dv/dt) was significantly reduced only at 1 × 10^?4M and above in Purkinje fibers and the membrane response curve was consistently shifted to the right by chlordiazepoxide. The ventricular muscle was little affected by chlordiazepoxide except for the shortened APD₅₀ and reduced dv/dt. Chlordiazepoxide exerted nerve blocking potency comparable to lidocaine in the crayfish giant axon. Voltage-clamp experiments in squid axon showed that chlordiazepoxide suppressed both components of membrane current, the transient inward sodium current being diminished far greater than the steady-state potassium current. These results demonstrate a direct action on cardiac and axonal membranes which may be partially responsible for the antiarrhythmic activity of this agent.     

Cardiac electrophysiological modulation by NS-7, a novel neuroprotective drug,of guinea pig ventricular muscles

Effects of NS-7 (1 to 100 microM), a novel neuroprotective drug, on the action potentials in guinea pig ventricular muscles were investigated at different stimulation frequencies, different extracellular Ca(2+) concentrations ([Ca](o)) and in the presence of inhibitors for selective delayed rectifier K(+) channels. A conventional microelectrode technique was carried out. NS-7 caused inhibitory actions on the action potential configuration in a concentration-dependent manner. NS-7 at less concentrations than 30 microM did not affect, but at 100 microM decreased the action potential amplitude (APA) and the maximum rate of depolarization (V(max)) by 11.1 +/- 2.3% (n = 14, P < 0.05) and by 24.3 +/- 2.6% (n = 14, P < 0.01), respectively. NS-7 at 100 microM also prolonged the 75 and 90% repolarizations of action potential duration (APD(75) and APD(90)) by 14.5 +/- 2.2% (n = 14, P < 0.05) and 20.2 +/- 2.4% (n = 14, P < 0.01), respectively, but it at any concentrations failed to affect the 50% repolarization of action potential duration (APD(50)). The resting potential was unaffected. These responses were almost reversible after 10-to 20-min washout. The stronger inhibition was caused at higher frequencies of stimulation. NS-7 prolonged the APD at lower [Ca](o) than 3.6 mM. In the presence of 5 microM E-4031 or 30 microM 293B, NS-7 increased further the APD. These results indicate that NS-7 at relatively higher concentrations produced inhibitory actions on the cardiac muscles, and that the APD prolongation and the V(max) inhibition induced by NS-7 are dependent on stimulation frequencies, but are independent of [Ca](o) levels, resulting in exhibition of its cardioprotective action.     

直链脂肪醇对豚鼠乳头肌慢动作电位的影响

本工作用相平面法观察和分析了乙醇、丁醇、己醇和辛醇对豚鼠乳头肌慢动作电位(APA,APD50,APD90,(?)_(max),(?)′_(max))及其所对应的钙电流(I_(max))和钾电流(I′_(max))的影响。结果表明:这四种脂肪醇对钙电流均有抑制作用,而对钾电流的影响,随碳原子数的加大从增强(乙醇)逐渐转化为削弱(已醇,辛醇)。并且碳链越长,产生这些效应所需脂肪醇的浓度越低,这提示醇的作用可能与它们的疏水性相关。     

在体兔心左室肌缺血中心区与边缘区跨膜电位的比较

实验在30只兔身上进行。利用浮置微电极技术,在心脏的缺血中心区、边缘区和非缺血区共记录了630个细胞的动作电位,其中270个细胞在阻断冠脉条件下进行记录,360个细胞在冠脉灌流条件下,造成心肌不同程度缺血后进行记录。同时,用棉线电极记录了各区心外膜电图ST段的变化。 阻断冠脉引起静息电位(RP)减小、动作电位振幅(APA)和零期最大除极速度(dv/dt)明显降低以及复极50％时程(APD_(50))和衰极90％时程(APD_(90))的显著缩短。缺血边缘区上述各指标的变化与ST 段抬高的程度均显著轻于缺血中心区。改变冠脉灌流血量造成心肌不同程度缺血的结果表明,当灌流血量为 50％时,在中心区所记录的静息电位和动作电位均与阻断冠脉后的边缘区相似;而灌流量为 0％时,在同一区所记录的静息电位和动作电位则与阻断冠脉后的中心区相似。另外,0％ 灌流时的ST 段抬高程度也显著高于灌流量为50％时的表现。这些结果提示,在兔急性心肌缺血早期,从缺血中心区和边缘区可记录到各具特征的动作电位,似有助于说明在缺血区有边缘区的存在。     

The effect of changes in cardiac frequency on left and right ventricular dP/dt max at different contractile states of the myocardium

In 17 canine heart-lung preparations the dependence of frequency potentiation of the right and left ventricular myocardium on the basic inotropic state of the heart was investigated. The effect of unipolar stimulation of the right atrium on dP/dt max in both ventricles was measured. The aortic pressure was maintained constant. Shortly after isolation of the heart, a stepwise increase of rate from 140 to 200 beats/min only had a very weak influence on left ventricular dP/dt max. With deterioration of the myocardium the frequency potentiation of dP/dt max increased considerably. End-diastolic pressure regularly decreased with rising cardiac frequency. Since the real positive inotropic effect is masked by the concomitant fall in diastolic loading, the end-diastolic pressure was maintained constant in a second group of 8 hearts during rate variation. The most pronounced inotropic effect was now found shortly after isolation of the heart. A rate increase of 30 beats/min resulted in a 20% rise of dP/dt max. The frequency potentiation decreased with deterioration of the heart resulting in a 12% dP/dt max increase at an estimated inotropic state of 50% of control. When the contractile state of the heart was improved above the control state by calcium application the frequency potentiation of the myocardium decreased. In the right ventricle similar results were obtained except for the fact that no significant correlation between the steepness of the frequency characteristics and the contractile state of the heart could be found when the end-diastolic pressure was kept constant.