氯离子通道与肺动脉血管张力

肺血管张力的变化直接影响着肺循环的压力,具有十分重要的生理和病理生理学意义。血管张力的维持与血管平滑肌细胞膜的离子通道密切相关。肺动脉平滑肌细胞(pul monary artery smoothmuscle cells,PASMCs)膜上主要分布有四种离子通道[1]如钾、钠、钙及氯离子通道。这些离子通道均参与和决定了平滑肌细胞膜的膜电位,而膜电位不仅是调节钙离子经由电压依赖性(或电压门控)钙通道(voltage-dependent Ca2+channels,VDC)内流,而且也是影响细胞内库存钙离子释放和平滑肌收缩装置对钙离子敏感性的关键的调节因素。通过调控钙离子的运输和膜电位,…     

心肌细胞离子通道与心律失常

从生物物理学的观点来看 ,离子通道应具有三个最重要性质 :通透性、选择性及门控机制。离子通道是以该通道允许通透的主要离子命名的 ,门控机制则调节着该离子的流动过程。细胞膜离子通道根据其门控机制可以分为三类 :电压门控性通道、配体门控性通道以及机械敏感性通道。另外 ,还有细胞器离子通道和细胞间离子通道。膜片钳技术与分子克隆、基因突变技术相结合 ,已成为一种非常有力的研究手段 ,从分子水平解释离子通道的孔道特性、动力学过程、结构和功能的关系以及功能的调节。本文将系统介绍心脏细胞离子通道的研究进展 ;根据各种离子通道…     

氯离子通道与肺动脉血管张力

肺血管张力的变化直接影响着肺循环的压力，具有十分重要的生理和病理生理学意义。血管张力的维持与血管平滑肌细胞膜的离子通道密切相关。肺动脉平滑肌细胞(pulmonary artery smooth muscle cells，PASMCs)膜上主要分布有四种离子通道如钾、钠、钙及氯离子通道。这些离子通道均参与和决定了平滑肌细胞膜的膜电位，而膜电位不仅是调节钙离子经由电压依赖性(或电压门控)钙通道(voltage-dependent Ca^2 channels，VDC)内流，而且也是影响细胞内库存钙离子释放和平滑肌收缩装置对钙离子敏感性的关键的调节因素。通过调控钙离子的运输和膜电位，离子通道参与了产生和调节血管张力的各个方面。     

氯离子通道活性与缺氧性肺动脉高压

在缺氧性肺血管收缩(HPV)的发病机制中,钾通道和钙通道均发挥了重要作用。但对于氯离子通道在HPV中的作用有待进一步研究。已经发现:低氧引起肺动脉内皮细胞功能紊乱,致血管收缩物质释放增加,如内皮素、血管紧张素Ⅱ、去甲肾上腺素、ATP和组胺等,它们大多可激活钙激活性氯通道,氯离子外流,细胞膜去极化,最终使肺动脉平滑肌收缩,产生HPV。所以钙激活性氯通道的激活在HPV的发生过程中起了关键作用。氯通道阻断剂对低氧性肺动脉高压的防治可能具有一定的临床应用前景。     

钙离子激活的氯离子通道-1与呼吸疾病的气道黏液高分泌

氯离子通道对维持人体正常的生理功能有着重要的作用。它可以维持细胞膜的稳定性,并且参与离子和体液的转运。氯离子通道在肌强直(myotonia)、肺囊性纤维化(CF)的发病中起着重要作用,并且已经得到广泛的研究。在这两种疾病中,分别存在电压依赖性氯离子通道(CLC)和肺囊性纤维化跨膜传导调节体(cystic fibosis transmembraneconductance regulator,CFTR)的缺陷。近年来研究发现了一个新的蛋白家族钙离子激活的氯离子通道(CLCA)广泛分布于人体的多种组织,其与卵细胞受精、上皮组织的跨膜体液转运、细胞复极、嗅觉传导、心肌细胞不应期、…     

氯离子通道活性与缺氧性肺动脉高压

在缺氧性肺血管收缩（HPV）的发病机制中，钾通道和钙通道均发挥了重要作用。但对于氯离子通道在HPV中的作用有待进一步研究。已经发现：低氧引起肺动脉内皮功能紊乱，致血管收缩物质释放增加，如内皮素、血管紧张素Ⅱ、去甲肾上腺素、ATP和组胺等，它们大多可激活钙激活性氯通道，氯离子外流，细胞膜去极化，最终使肺动脉平滑肌收缩，产生HPV。所以钙激活性氯通道的激活在HPV的发生过程中起了关键作用。氯通道阻断剂对低氧性肺动脉高压的防治可能具有一定的临床应用前景。     

氯离子通道与缺血性卒中

缺血性卒中是发病率和致残率最高的疾病之一.高血压是公认的缺血性卒中最重要的独立危险因素,在高血压发展过程中出现的血管重构是引发缺血性卒中的病理学基础.研究表明,血管平滑肌细胞异常增殖和凋亡都将导致血管重构.此外,脑缺血再灌注可导致神经元损伤和凋亡.近来的研究表明,血管重构和神经元凋亡都与氯离子通道有关.至少3种氯离子通道参与这些过程:容积调控的氯离子通道、钙激活的氯离子通道以及囊性纤维跨膜电导调节体.文章就这3种氯离子通道在血管重构、神经元凋亡以及缺血性卒中中的作用进行了综述.     

钙离子激活的氯离子通道-1与呼吸疾病的气道黏液高分泌

氯离子通道对维持人体正常的生理功能有着重要的作用。它可以维持细胞膜的稳定性，并且参与离子和体液的转运。氯离子通道在肌强直(myotonia)、肺囊性纤维化(CF)的发病中起着重要作用，并且已经得到广泛的研究。在这两种疾病中，分别存在电压依赖性氯离子通道(CLC)和肺囊性纤维化跨膜传导调节体(cystic fibosis transmembrane conductanceregulator，CFTR)的缺陷。近年来研究发现了一个新的蛋白家族——钙离子激活的氯离子通道(CLCA)广泛分布于人体的多种组织，其与卵细胞受精、上皮组织的跨膜体液转运、细胞复极、嗅觉传导、心肌细胞不应期、平滑肌细胞张力和细胞黏附等多种生理过程密切相关，     

细胞外La~(3+)对内向整流钾通道(IRK1)的阻断作用

本文采用双微电极电压钳 (TEV)法研究细胞外La3+对非洲爪蟾卵母细胞表达的内向整流钾通道(IRK1)的阻断作用。细胞外La3+浓度分别为 0 ,0 1,0 3,1,3和 10mmol/L ,K+浓度为 90mmol/L ,可见La3+对IRK1的瞬间电流 (施加电压后 1 5ms)具有La3+浓度依赖性、时间依赖性和电压依赖性阻断作用 ;阻断剂La3+对IRK1的门控特性和外向电流几乎无影响作用 ;细胞外加La3+后反转电位没有变化 ,因而IRK1对之不通透。细胞外La3+在减少IRK1电导的同时增加IRK1的归一化电导。三级指数拟合的结果表明 :拟合的时间常数不随La3+浓度的增减而增减 ,这表明细胞外La3+对IRK1的抑制作用可能通过了表面电荷机制或La3+在通道中的阻断位点在通道表面。因为La3+浓度较低时 ,阻断的效力与La3+浓度较高时的差异不大 ,所以La3+不会通过表面电荷机制进行IRK1阻断的 ,因此La3+是IRK1的一种快速开通道阻断剂 ,其阻断位点在通道表面     

BQ123对慢性低氧大鼠肺动脉平滑肌细胞KV1.5表达的影响

内皮素1(ET-1)可浓度依赖性的抑制大鼠肺动脉平滑肌细胞(PASMCs)电压门控钾电流(IKv)，但ET-1对PASMCs电压门控钾通道(Kv)基因表达的调节目前尚少见报道，本组研究拟从mRNA和蛋白水平，阐明内皮素受体拮抗剂BQ123对PASMCs Kv1．5表达的影响。     

Involvement of chloride channels in hepatic copper metabolism: ClC-4 promotes copper incorporation into ceruloplasmin

BACKGROUND & AIMS: Copper transport in hepatocytes is regulated by the interaction of multiple pumps, chaperones, and accessory proteins. Intracellular chloride channels are essential for copper metabolism in yeast but their role in Cu transport in hepatocytes is unknown. The aim of this study was to determine whether chloride channels are modulators of copper incorporation into ceruloplasmin (CP). METHODS: The effects of chloride concentration and chloride channel expression on secretion of holoCp and apoCp was measured by gel electrophoresis and immunoblotting. ClC family chloride channel expression in hepatocytes was determined by Western blotting. The association of ClC-4 and the Wilson's disease protein (ATP7B) was determined by co-immunoprecipitation. RESULTS: Chloride substitution reduced total Cp secretion and the ratio of secreted holoCp to apoCp (P = 0.038). The role of specific chloride channels was examined by cotransfection of ceruloplasmin and the chloride channel. Overexpression of ClC-4 doubled copper incorporation into ceruloplasmin (P = 0.011), whereas identical overexpression of ClC-3 had no effect. The effect of ClC-4 was most pronounced under copper-limiting conditions in which it increased copper incorporation more than 4-fold (P = 0.037). ClC-4 protein was abundant in hepatocyte membranes and was localized in intracellular vesicles containing ATP7B.CONCLUSIONS: ClC-4 is an intracellular chloride channel that stimulates copper incorporation into ceruloplasmin, probably by improving the efficiency of the ATP7B copper pump. It is thus an important component of the regulation of hepatic copper transport and may modulate Cu transport rates during copper deficiency, Wilson's disease, and other copper toxicosis syndromes.     

Voltage- and calcium-dependent gating of TMEM16A/Ano1 chloride channels are physically coupled by the first intracellular loop

Ca(2+)-activated Cl(-) channels (CaCCs) are exceptionally well adapted to subserve diverse physiological roles, from epithelial fluid transport to sensory transduction, because their gating is cooperatively controlled by the interplay between ionotropic and metabotropic signals. A molecular understanding of the dual regulation of CaCCs by voltage and Ca(2+) has recently become possible with the discovery that Ano1 (TMEM16a) is an essential subunit of CaCCs. Ano1 can be gated by Ca(2+) or by voltage in the absence of Ca(2+), but Ca(2+)- and voltage-dependent gating are very closely coupled. Here we identify a region in the first intracellular loop that is crucial for both Ca(2+) and voltage sensing. Deleting (448)EAVK in the first intracellular loop dramatically decreases apparent Ca(2+) affinity. In contrast, mutating the adjacent amino acids (444)EEEE abolishes intrinsic voltage dependence without altering the apparent Ca(2+)affinity. Voltage-dependent gating of Ano1 measured in the presence of intracellular Ca(2+) was facilitated by anions with high permeability or by an increase in [Cl(-)](e). Our data show that the transition between closed and open states is governed by Ca(2+) in a voltage-dependent manner and suggest that anions allosterically modulate Ca(2+)-binding affinity. This mechanism provides a unified explanation of CaCC channel gating by voltage and ligand that has long been enigmatic.     

Staurosporine诱导心肌细胞氯通道电流的电生理学特性

目的 探讨staurosporine（STS）诱导乳鼠心肌细胞凋亡的早期,凋亡性容积减少（AVD）发生时,是否有氯通道电流的产生及其电生理学特性。方法 分别采用低渗组的灌流液和含STS的等渗组灌流液处理原代培养的SD乳鼠心肌细胞,以膜片钳全细胞记录法记录电流。结果 ①以低渗灌流液处理的心肌细胞时,可记录到氯通道电流。该电流呈现类似容积敏感性氯通道电流(volume-sensitive chloride channel current,ICl,Vol)的电生理学特性:即外向整流性、高电位刺激下的时间依赖性失活及对氯通道阻断剂4,4′-异二硫氮氐2,2′-二磺酸(DIDS)的敏感性。②以含4 μmol/L STS的等渗液灌流心肌细胞时,也可记录到类似低渗诱导产生的氯通道电流,具有ICl,Vol的电生理学特性,且用氯通道阻断剂500 μmol/L DIDS后,在+40 mV、+60 mV、+80 mV及+100 mV时,能够明显电压依赖性地阻断该电流。结论 首次应用STS在培养乳鼠心肌细胞中记录到类似容积敏感性氯通道电流。     

An outwardly rectifying chloride channel in human atrial cardiomyocytes

Introduction: Among a range of chloride channels, outwardly rectifying Cl^? channels have been reported in the heart of various species. Although the anionic current carried by this channel has been subjected to intense electrophysiological investigations, paradoxically no examination of single‐channel currents has been reported for human cardiomyocytes. Methods and Results: Using the cell‐attached and cell‐free configurations of the patch‐clamp technique, we have characterized the properties of an outwardly rectifying chloride current (ORCC) at the unitary level in freshly isolated human atrial cardiomyocytes. In excised inside‐out patches, the channel presented a nonlinear I/V relationship with a conductance of 76.5 ± 14.7 pS in the positive voltage range and 8.1 ± 2 pS in the negative voltage range, indicating an outward rectification. Preincubation with the protein kinase C activator phorbol 12‐myristate 13‐acetate (PMA) significantly increased the number of spontaneously active channels observed. The channel was Cl^? selective (Cl^? to Na⁺ permeability ratio, P_Cl/P_Na= 18) with the permeability sequence I^? > Br^? > Cl^? > F^? > gluconate. It was blocked by the classical Cl^? channels blockers glibenclamide, NPPB, SITS, and DIDS. Channel activity was not dependent upon internal calcium concentration. In the cell‐attached configuration, ORCC channel activation was observed under perfusion of a hypotonic solution. Conclusion: Human atrial myocytes express an outwardly rectifying Cl^? channel that is sensitive to PKC activation. This channel shares biophysical and pharmacological properties with the swelling‐activated chloride current implicated in cardiac pathologies such as myocardial ischemia and dilated cardiopathies.     

Gating of single Shaker potassium channels in Drosophila muscle and in Xenopus oocytes injected with Shaker mRNA.

The voltage-dependent gating mechanism of single A-type potassium channels coded for by the Shaker locus of Drosophila was studied by single-channel recording. A-type channels expressed in Xenopus oocytes injected with Shaker B and Shaker D mRNA exhibited gating and voltage dependence that were qualitatively similar to those of the native Shaker A-types channels from embryonic myotubes. In all three channel types the molecular transition rates leading to the first opening were voltage-dependent, whereas all transitions after the first opening, including inactivation, were independent of voltage. While these channels exhibit some quantitative differences in their transition rates that account for the observed differences in macroscopic currents, in all three cases the voltage dependence of the macroscopic currents is determined by a voltage dependence in the time to first opening. This gating mechanism is similar to that of the vertebrate voltage-gated sodium channel and, together with the sequence similarities in the S4 region of the proteins, suggests a conserved mechanism for activation and inactivation.     

Gating currents associated with intramembrane charge displacement in HERG potassium channels

HERG (human ether-a-go-go-related gene) encodes a delayed rectifier K+ channel vital to normal repolarization of cardiac action potentials. Attenuation of repolarizing K+ current caused by mutations in HERG or channel block by common medications prolongs ventricular action potentials and increases the risk of arrhythmia and sudden death. The critical role of HERG in maintenance of normal cardiac electrical activity derives from its unusual gating properties. Opposite to other voltage-gated K+ channels, the rate of HERG channel inactivation is faster than activation and appears to be intrinsically voltage dependent. To investigate voltage sensor movement associated with slow activation and fast inactivation, we characterized HERG gating currents. When the cut-open oocyte voltage clamp technique was used, membrane depolarization elicited gating current with fast and slow components that differed 100-fold in their kinetics. Unlike previously studied voltage-gated K+ channels, the bulk of charge movement in HERG was protracted, consistent with the slow rate of ionic current activation. Despite similar kinetic features, fast inactivation was not derived from the fast gating component. Analysis of an inactivation-deficient mutant HERG channel and a Markov kinetic model suggest that HERG inactivation is coupled to activation.     

Gating transitions in the selectivity filter region of a sodium channel are coupled to the domain IV voltage sensor

Voltage-dependent ion channels are crucial for generation and propagation of electrical activity in biological systems. The primary mechanism for voltage transduction in these proteins involves the movement of a voltage-sensing domain (D), which opens a gate located on the cytoplasmic side. A distinct conformational change in the selectivity filter near the extracellular side has been implicated in slow inactivation gating, which is important for spike frequency adaptation in neural circuits. However, it remains an open question whether gating transitions in the selectivity filter region are also actuated by voltage sensors. Here, we examine conformational coupling between each of the four voltage sensors and the outer pore of a eukaryotic voltage-dependent sodium channel. The voltage sensors of these sodium channels are not structurally symmetric and exhibit functional specialization. To track the conformational rearrangements of individual voltage-sensing domains, we recorded domain-specific gating pore currents. Our data show that, of the four voltage sensors, only the domain IV voltage sensor is coupled to the conformation of the selectivity filter region of the sodium channel. Trapping the outer pore in a particular conformation with a high-affinity toxin or disulphide crossbridge impedes the return of this voltage sensor to its resting conformation. Our findings directly establish that, in addition to the canonical electromechanical coupling between voltage sensor and inner pore gates of a sodium channel, gating transitions in the selectivity filter region are also coupled to the movement of a voltage sensor. Furthermore, our results also imply that the voltage sensor of domain IV is unique in this linkage and in the ability to initiate slow inactivation in sodium channels.     

Allosteric gating mechanism underlies the flexible gating of KCNQ1 potassium channels

KCNQ1 (Kv7.1) is a unique member of the superfamily of voltage-gated K(+) channels in that it displays a remarkable range of gating behaviors tuned by coassembly with different β subunits of the KCNE family of proteins. To better understand the basis for the biophysical diversity of KCNQ1 channels, we here investigate the basis of KCNQ1 gating in the absence of β subunits using voltage-clamp fluorometry (VCF). In our previous study, we found the kinetics and voltage dependence of voltage-sensor movements are very similar to those of the channel gate, as if multiple voltage-sensor movements are not required to precede gate opening. Here, we have tested two different hypotheses to explain KCNQ1 gating: (i) KCNQ1 voltage sensors undergo a single concerted movement that leads to channel opening, or (ii) individual voltage-sensor movements lead to channel opening before all voltage sensors have moved. Here, we find that KCNQ1 voltage sensors move relatively independently, but that the channel can conduct before all voltage sensors have activated. We explore a KCNQ1 point mutation that causes some channels to transition to the open state even in the absence of voltage-sensor movement. To interpret these results, we adopt an allosteric gating scheme wherein KCNQ1 is able to transition to the open state after zero to four voltage-sensor movements. This model allows for widely varying gating behavior, depending on the relative strength of the opening transition, and suggests how KCNQ1 could be controlled by coassembly with different KCNE family members.