正常肠系膜动脉平滑肌细胞钙激活钾通道活性的观察

为了解人体正常肠系膜动脉平滑肌细胞钙激活钾通道的特性 ,取 2 4例人体正常肠系膜动脉小枝节段 ,用酶消化法获取标本细胞 ,以膜片钳制技术检测钙激活钾通道的活性 ,通过Pclamp专用软件实时采样记录其平均开放时间、平均关闭时间及平均开放概率等。结果发现 ,人体肠系膜动脉平滑肌细胞钙激活钾通道开放具有明显电压依赖性 ,在对称性高钾液中 ,电流 -电压关系曲线在 10～ 6 0mV范围内可被直线拟合。在细胞吸附式膜片和内面向外膜片中 ,通道电导分别为 192 .3± 2 9.2Ps和 2 0 2 .5± 5 8.3Ps。开放概率和开放数目随Ca2 + 浓度的增加而增加 ,膜内面应用四乙胺可减少通道开放概率及电流幅值。提示人体肠系膜动脉平滑肌细胞钙激活钾通道与人体其他血管相似 ,主要为大电导钙激活钾通道 ,具有电压和钙浓度双重依赖性。     

离子通道水平上内皮素缩血管机制的研究进展

９０年代以来，用膜片钳、荧光探针等先进手段，在细胞膜和镶嵌着通道蛋白的人工脂膜上，观察了跨膜的内向离子流和外向离子流。已证明Ｌ型、Ｔ型、Ｎ型电压依赖性钙通道，ＢＫ型钙依赖性钾通道，以及一种钙依赖性非选择性阳离子通道参与内皮素对血管的调控机制。     

平滑肌钙通道调节

平滑肌钙通道调节平滑肌钙通道包括Ｌ型及Ｔ型电压依赖性钙通道、受体门控钙通道、牵张激活钙通道和背景钙通道，其中激素、递质及胞内信息分子对电压依赖性钙通道作用的研究最多，现介绍如下。一、激素和神经递质对钙电流的调节许多血管活性物质的作用涉及电压依赖性钙通...     

心脏钠电流与其他离子流的相互作用及其临床意义

心肌细胞膜上的离子流共同参与心脏在生理及病理下的电活动。钠离子流（INa）参与心肌细胞动作电位（AP）的除极和复极过程,对AP的传导有重要作用。故研究心脏钠通道与各离子通道的离子流相互关系及影响,意义尤为重要。本文综述了钠离子流与心脏其他离子流间的相互作用关系,试图从离子流相互作用的角度解释心律失常的发生机制。     

低血钙性心肌病:一种可逆性心肌病

自从1883年Ringer氏证明离体灌注心肌的收缩性与外界钙浓度呈正相关以来,已经明了钙在心肌力学中的重要性。在心肌细胞内,钙离于是动作电位的发生、电兴奋与肌肉收缩之间的联系(兴奋-收缩耦联)及能量控制与利用中的关键性成分。此外通过钙依赖性的活动过程可以改变冠状动脉的张力,从而改变冠状动脉的血流。因此,对钙代谢的异常,特别是钙的缺乏,可以影响心脏功能,并且在某些病例中引起临床表现的心脏病。生理机制: 钙离子经慢内向通道或钙依赖性通道流过心肌细胞膜,该通道具有电压依赖性和受     

电压依赖性钾通道与哮喘发病机制的相关性研究

目的探讨钾通道开放剂（KCOs）对组胺作用后电压依赖性钾通道（Kv）及哮喘豚鼠支气管平滑肌细胞（BSMCs）Kv的作用。方法利用膜片钳技术细胞贴附式方法测定正常豚鼠支气管平滑肌细胞Kv的开放时间快慢成分（rfast、rslow），关闭时间及组胺作用后Kv的开放时间、关闭时间；哮喘豚鼠支气管平滑肌细胞Kv的开放时间、关闭时间及KCOs对二者的影响。结果组胺可明显缩短豚鼠BSMCs电压依赖性钾通道开放时间，延长关闭时间，与正常对照组比较差异有显著性（P〈0．001）；哮喘组与正常对照组比较开放时间,rfast、rslow明显缩短，关闭时间延长，二者相比有显著性差异（P〈0．001）。KCOs可延长组胺作用后及哮喘豚鼠BSMCs钾通道的开放时间，缩短关闭时间，二者相比有显著性差异（P〈0．001）。结论哮喘豚鼠BSMCs电压依赖性钾通道活性降低，组胺可缩短Kv的开放时间，延长Kv的关闭时间可能为哮喘的发病机制之一。KCOs可增加哮喘豚鼠支气管平滑肌Kv的活性，由此可能达到治疗哮喘的作用。     

主动脉平滑肌钙激活钾通道的增龄变化

目的研究不同月龄大鼠主动脉平滑肌细胞钙激活钾通道的活性,探讨老化过程中血管平滑肌细胞钙激活钾通道的变化。方法取三组Wistar大鼠(分别为1月龄、6月龄、20月龄各20只)主动脉用酶消化法获得单个平滑肌细胞。以膜片钳技术检测细胞钙激活钾通道的活性,记录不同钳制电压下单通道电流的平均开放时间、平均关闭时间、平均开放概率、电流幅值,并绘制成电流—电压关系曲线。对比各月龄组Wistar大鼠主动脉平滑肌细胞钙激活钾通道活性。结果(1)各月龄组大鼠主动脉平滑肌细胞随着膜电位从+10 mV向+60 mV方向去极化,钙激活钾通道的电流强度逐渐加大,但加大幅度随月龄增加而降低。1月龄、6月龄和20月龄大鼠主动脉平滑肌细胞钙激活钾通道的电导值分别为192±47 ps、177±56 ps和163±35 ps,但差异无统计学意义(P>0.05)。(2)在内面向外式膜片上,20月龄和1月龄大鼠主动脉平滑肌细胞钙激活钾通道平均开放概率分别为0.009±0.001和0.015±0.004,两组比较具有显著性差异(P<0.01)。20月龄和1月龄大鼠主动脉平滑肌细胞钙激活钾通道平均关闭时间分别为2 260±653和2 512±185*,两组比较具有显著性差异(P<0.01)。(3)在同样的对称性高钾浴液中,加入不同浓度钙后,发现钙对各月龄组大鼠主动脉平滑肌细胞钙激活钾通道均有明显的激活作用,表现为平均开放概率逐渐加大,平均关闭时间逐渐缩短。但对各月龄相同钙浓度间比较发现,6月龄组平均开放概率比1月龄加大,而20月龄组平均开放概率和平均开放时间比6月龄和1月龄组均显著降低。结论大鼠主动脉平滑肌细胞钙激活钾通道的活性随着年龄增大而下降。     

有氧运动抑制衰老大鼠脑动脉平滑肌STOC/BKCa功能下调

目的　探讨有氧运动训练对衰老大鼠脑动脉平滑肌细胞全细胞K⁺电流、自发瞬时外向电流及大电导钙激活钾通道生物物理特性的影响。方法　19～21月龄雄性Wistar大鼠12只（老年组）,随机分为安静组和有氧运动组,并选用2月龄Wistar大鼠安静处理作为青年对照组。12周后取脑动脉,急性分离动脉平滑肌细胞。分别采用膜片钳全细胞模式、穿孔膜片钳模式和单通道内面向外模式观察运动对全细胞K⁺电流、自发瞬时外向电流和大电导钙激活钾通道门控特性的影响。结果　安静组全细胞K⁺电流密度及对Iberiotoxin敏感性降低;安静组自发瞬时外向电流幅值降低,频率无明显变化;安静组大电导钙激活钾通道平均开放概率和平均开放时间显著低于青年对照组,而平均关闭时间高于青年对照组;电压依赖性和钙敏感性亦显著下降;与安静组相比,有氧运动可以增加全细胞K⁺电流密度、自发瞬时外向电流幅值及大电导钙激活钾通道平均开放概率、电压依赖性和钙敏感性来实现对大鼠脑动脉平滑肌自发瞬时外向电流/大电导钙激活钾通道功能的保护作用。结论　长期规律有氧运动可以减弱衰老所致的大鼠脑动脉平滑肌细胞大电导钙激活钾通道功能下调,这可能是有氧运动改善衰老动脉功能的重要机制之一。     

心脏Nav1.5相互作用蛋白与心律失常

电压门控钠离子通道负责心肌细胞动作电位的产生、传导和持续时间.钠离子通道由核心α亚单位Nav1.5和1～4个辅助β亚单位构成.Nav1.5是钠离子通道孔形成的亚基单位,可以独立发挥作用.编码Nav1.5基因的突变可以改变钠离子通道电生理特性,导致"钠离子通道病",包括先天性和获得性长QT综合征(LQTS)、Brugada综合征(BrS)、新生儿猝死综合征(SIDS)、心脏传导系统障碍、病态窦房结综合征、心房颤动(房颤)及扩张性心肌病等.     

电压门控钠离子通道与内脏高敏感性

电压门控钠离子通道是一种多亚基跨膜糖蛋白,在神经元动作电位的产生和传播过程中起着关键作用,因此它与内脏高敏感性关系密切。阐明电压门控钠离子通道与内脏高敏感性的关系有助于探索某些胃肠道功能性疾病治疗的新方法。     

Effects of trimetazidine on action potentials and membrane currents of guinea-pig ventricular myocytes

The effects of trimetazidine on membrane potentials and membrane currents of enzymatically isolated guinea-pig ventricular cells were studied with the use of giga-seal suction pipettes for patch clamp. Trimetazidine (3 X 10(-5) M) decreased the action potential duration from 433 +/- 179 ms (mean and S.D., n = 9) to 319 +/- 156 ms within 8 mins. In voltage clamp experiment, trimetazidine at a concentration of 1.5 X 10(-4) M decreased the peak amplitude of calcium current by 40% (0.92 +/- 0.46 nA to 0.55 +/- 0.19 nA, mean +/- S.D., n = 5). The effect on calcium current was rate-dependent, e.g., at 1 Hz, trimetazidine blocked a larger fraction of the calcium current than at 0.2 Hz. The drug decreased the conductance of potassium current which flows via inward rectifier potassium channel from 28 +/- 11 nS to 19 +/- 10 nS, n = 5, P less than 0.05). Trimetazidine shifted the steady state current-voltage relationship outward at potentials positive to -20 mV. This shift was not due to the enhanced time- and voltage-dependent outward current (Ik). From these findings, it was concluded that trimetazidine shortens action potential duration by blocking the calcium channels with increases in steady state outward current or a possible blockade of non-inactivated component of the calcium current, at the plateau potentials. The reduction of calcium current and of inward rectifier potassium current may protect the cardiac cells from accumulation of calcium ions and from loss of potassium ions, in the presence of ischemia.     

稳心颗粒甘松提取物对大鼠心室肌细胞钠电流和瞬时外向钾电流激活动力学的影响

目的研究步长稳心颗粒中甘松提取物对大鼠心室肌细胞钠电流(INa)、瞬时外向钾电流(Ito)激活动力学的影响。方法采用全细胞膜片钳技术,研究10 g/L甘松提取物对急性分离的成年大鼠心室肌细胞INa、Ito激活动力学的影响。结果①10 g/L甘松提取物使大鼠心室肌细胞INa峰值(INa,max)从-58.96±2.71 pA/pF降至-31.66±1.29 pA/pF(n=5,P<0.01);②10 g/L甘松提取物使Ito峰值(Ito,max)由3.40±1.52 pA/pF降到1.43±0.64 pA/pF(n=7,P<0.05)。10 g/L甘松提取物对INa和Ito的抑制率分别达38.2%和57.9%。结论10 g/L甘松提取物对大鼠心室肌细胞INa、Ito具有显著抑制作用。     

神经元型钠通道在室性心律失常发生机制中的作用

室性心律失常是导致心脏性猝死最重要的原因,其发生机制与心室肌细胞离子电流紊乱有密切关系。近期研究发现,神经元型钠通道也表达于心脏,是介导晚钠电流的重要通道,可通过以下机制触发室性心律失常:(1)神经元型钠通道活性异常增高引起内向电流增大,破坏动作电位平台期电位平衡,直接引起细胞膜去极化,发生早后除极。(2)神经元型钠通道与钙调控蛋白在T管微域内共定位,其介导的Na+内流通过增强钙调控蛋白功能引起舒张期Ca2+释放,发生迟后除极。(3)晚钠电流具有速率依赖性和分布异质性,可增大复极离散,构成功能性折返的发生基质。现就神经元型钠通道在室性心律失常发生中的作用做一综述。     

Elevation of intracellular calcium by muscarinic receptor activation induces a block of voltage-activated rat ether-à-go-go channels in a stably transfected cell line.

We have studied the properties of r-eag voltage-activated potassium channels in a stably transfected human embryonic kidney cell line. It was found that r-eag channels are rapidly and reversibly inhibited by a rise in intracellular calcium from 30 to 300 nM. The inhibition does not appear to depend on the activity of calcium-dependent kinases and phosphatases. The effect of calcium on r-eag channel activity was studied in inside-out membrane patches. Calcium inhibited r-eag channel activity with a mean IC50 of 67 nM. Activation of muscarinic receptors, generating calcium oscillations in the transfected cells, induced a synchronous inhibition of r-eag mediated outward currents. This shows that calcium can mediate r-eag current inhibition following muscarinic receptor activation. The data indicate that r-eag channels are calcium-inhibitable voltage-activated potassium channels.     

The calcium channel blocker nitrendipine blocks sodium channels in neonatal rat cardiac myocytes

The dihydropyridine calcium channel blocker, nitrendipine, was studied for its effects on the sodium current of single cultured ventricular cells from neonatal rats. The patch-clamp method of recording whole cell currents was used, and sodium currents were isolated by suppressing potassium and calcium currents. Potassium currents were blocked by replacing potassium with cesium in the internal and external solutions and by adding tetraethylammonium chloride and 4-aminopyridine in the external solution; calcium current was blocked by replacing calcium with cobalt in the external solution. At low frequencies (0.1 Hz), nitrendipine reduced sodium currents without any significant change in the current-voltage relation. The block was dose dependent, and assuming a single occupancy model with complete block, had a half-maximum value of 3 X 10(-6) M at a holding potential of -80 mV where half the sodium channels are activatable. This value is within the range of the Kd's that have been reported for low-affinity dihydropyridine-binding sites found in cardiac sarcolemmal vesicles. In the presence of nitrendipine, the inactivation curve was shifted to hyperpolarized potentials. The block was greater with pulse intervals shorter than 1000 msec, and repriming was prolonged in the presence of the drug. These effects are similar to those of local anesthetics of the tertiary amine class, such as lidocaine. The block was relieved by the dihydropyridine agonist Bay K8644. The results are interpreted as indicating that dihydropyridines react with sodium channels.     

Tetrodotoxin: sodium channel specific anti-arrhythmic activity

Many Class I anti-arrhythmic drugs not only block the cardiac sodium channel but also block the calcium and/or potassium channels. The hypothesis tested in this study was that sodium channel blockade without blockade of calcium or potassium channels produced anti-arrhythmic activity in the treatment of malignant ventricular arrhythmias. The arrhythmia model consists of ventricular fibrillation induced by critically timed single extrastimuli at twice diastolic pacing threshold following 15 minutes of ischaemic injury in a rabbit heart perfused in vitro. Preparations were randomly assigned to either tetrodotoxin (a selective sodium channel blocking toxin) or vehicle. Ventricular fibrillation occurred in all vehicle treated preparations in response to single extrastimuli following ischaemic injury. Treatment with tetrodotoxin at concentrations of 0.1 to 1.0 micromolar protected some hearts from fibrillation, while at concentrations above 3 micromolar ventricular fibrillation was not inducible. Tetrodotoxin produced concentration dependent increases in ventricular effective refractory period and conduction time in the infarct zone which were associated with anti-arrhythmic activity. No concentration dependent change in action potential duration was seen with tetrodotoxin. Thus the electrophysiological and anti-arrhythmic activities of tetrodotoxin in this model demonstrate that the property of selective sodium channel blockade is sufficient to produce anti-arrhythmic activity.     

Channel-mediated calcium current in the heart

Summary Calcium ions play an important role in the regulation of heart functions. Calcium ions may enter or leave the myocardial cell through various mechanisms, including several exhange mechanisms and pumps. This review concentrates on the influx of calcium ions through channels in the sarcolemma, resulting in an electric current flow. The calcium current plays an important role in the maintenance of the action potential duration, in the generation of pacemaker activity, and in the initiation of contraction.The calcium current displays both activation and a subsequent inactivation when the membrane potential is changed in a stepwise fasion. Previously, the activation was thought to occur rather slowly, hence the name slow inward current. Recent evidence suggests that the calcium current occurs much faster and that two types of calcium currents might exist, differing in their selectivity to other ions and in their sensitivity to membrane potential and to drugs.The calcium current is modulated by several factors. Beta-adrenergic stimulation increases the calcium current by increasing the opening probability of the calcium channel. The effects of acetylcholine are less well described. There also exists a class of drugs, called calcium channel blockers (or calcium antagonists) that decrease the flow of calcium ions through calcium channels.It is not quite clear how the calcium current is changed during myocardial ischemia. Factors that may reduce the calcium current during ischemia are the increased extracellular potassium concentration, metabolic inhibition and a decreased ATP level, and acidosis. Raised levels of intracellular cAMP, however, should lead to an increased calcium current.     

Modification of cardiac ionic currents by photosensitizer-generated reactive oxygen

The effects of reactive oxygen species (ROS) generated by light and the photosensitizer Rose Bengal on ionic currents in single frog atrial cells were investigated. The excitatory inward sodium and calcium currents were both suppressed by ROS as was the outward, delayed rectifier potassium current. The inactivation kinetics of the sodium current were slowed markedly whereas the kinetics of calcium current inactivation were much less affected and potassium current activation was not changed. The sodium current-voltage relationship was shifted in the depolarizing direction by ROS whereas the voltage-dependencies of both the calcium and potassium currents were not affected. In addition to suppressing the time- and voltage-dependent sodium, calcium, and potassium currents, ROS enhanced a time-independent current which was outwardly directed at positive membrane potentials. However, the induction of this time-independent current required longer ROS exposure than was required to significantly suppress the other currents. The rapid onset of ROS-induced suppression of calcium and potassium currents followed by a later enhancement of a time-independent current can explain ROS-induced changes in action potential duration. Brief ROS exposure increased action potential duration whereas longer exposure reduced action potential duration.     

甲状腺素诱发大鼠心肌肥厚时瞬时外向钾电流、内向整流钾电流和钙电流的变化

目的 研究甲状腺素诱发大鼠心肌肥厚模型的心肌细瞬时外向钾电流、内向整流钾电流和钙电流的变化。方法 以ipL-甲门面腺素造成大鼠心肌肥厚模型后,用膜片钳技术记录心肌细胞瞬时外向钾电流、内向整流钾电流和L型钙电流。结果 肥厚组心肌细胞瞬时外向钾电流幅度和心坎产增加,激活动力学特性无改变;内向整流钾电流幅度和密度也增加,激活动力学特性也无改变;而钙电流幅度、细胞膜电容增加,电流密度不变,半数激活电压（V1/2）向负电位方向移动,斜率（k)减小。结论 在甲状腺素诱发大鼠心肌肥厚模型中瞬时外向钾电流、内向整流钾电流和钙电流特性均发生了变化,这是造成肥厚心肌电生理异常的离子基础。     

Patch-clamp study of the ionic currents underlying action potentials in cultured frog pituitary melanotrophs

The ionic conductance mechanisms underlying the action potential behaviour of frog melanotrophs in primary culture were studied by using the patch-clamp technique in whole-cell configuration. The action potentials spontaneously generated by these cells were predominantly sodium spikes with a calcium component. Voltage-dependent sodium, calcium, potassium and calcium-activated potassium currents were identified and analysed separately. The voltage-dependent sodium current was characterized by its fast kinetic, its low-threshold activation, its voltage-dependent inactivation and a tetrodotoxin sensitivity. Calcium currents were identified on the basis of their ionic selectivity to divalent cations (Ba2+, Ca2+, Co2+) and their time course. Only two of the three well-documented calcium currents could be detected in frog melanotrophs. A sustained calcium current (ICaS) and an inactivating calcium current (ICaN) were elicited by step depolarizations up to -20 mV. ICaN inactivated for membrane potentials more positive than -50 mV; its inactivation appeared to be both voltage- and calcium-dependent. Transient calcium current (ICaT) has never been observed. Two types of potassium currents were identified: voltage-dependent potassium (IKV) and calcium-activated potassium currents, (IK[Ca]). They were both suppressed by tetraethylammonium chloride, whereas only IK(Ca) was blocked by cobalt. These major ionic currents underlying spontaneous electrical activity are assumed to be involved in the process of alpha-melanocyte-stimulating hormone release. The present study provides the ground for future investigations regarding the relationships between the electrical and secretory activities in amphibian pars intermedia cells.