大电导钾离子通道(BK)结构与功能的研究进展

大电导钙离子激活钾通道(BK)是细胞膜上唯一接受细胞内Ca2+和膜电位双重调控的离子通道.最新发表的关于BK通道电镜结构及其胞质功能域的晶体结构的文章,第一次展示了BK通道各亚基的组装,并证实通道各功能域在通道门控机制中存在紧密的相互作用.近年来,针对BK通道的功能调节及其门控动力学模拟的研究取得较多进展,有助于更好地理解BK通道发挥生理功能的门控机制,并揭示BK通道相关疾病的病理生理学基础.     

BK通道的生物物理特性与门控及其最新研究进展

BK_(Ca)通道是细胞膜上受Ca~(2+)和膜电位双重调控的离子通道,其与细胞信号系统偶联并发挥着重要作用,该通道高度表达于高等动物的多种组织.最近的研究证实,在心肌细胞膜上存在力敏感BK通道并参与了心脏收缩与舒张的调控.本文将介绍BK通道与L-型钙通道功能上的耦合,心肌细胞质膜力敏感BK通道门控和功能的研究,以及对基底刚度的响应.这有助于更好地理解力敏感离子通道相关心脏疾病的病理和生理学基础.     

昆虫中枢DUM神经元受体和离子通道电生理学研究进展

背侧不成对中间神经元(DUM)是一类位于多种昆虫腹神经索神经节背侧的神经元,能自发产生内源性超射动作电位。在DUM神经元细胞膜表达多种受体和离子通道,且电生理特性有别于哺乳动物中枢神经元膜上同种类型的受体和离子通道。目前已证实其细胞膜上表达K+通道、电压依赖的Na+通道、Ca2+敏感的Cl-通道、Ca2+通道、氯离子通道、乙酰胆碱受体、谷氨酸受体等多种离子通道和受体。近年来因膜片钳(patch-clamp)技术进展和对受体和离子通道研究的深入,该类神经细胞已用于杀虫剂选择性神经毒性研究和杀虫剂离体筛选。     

环核苷酸门控离子通道的结构、功能及活性调节

环核苷酸门控离子通道（cyclic nucleotide-gated ion channels,CNG）是非选择性的阳离子通道,直接被环核苷酸活化.6个不同基因编码CNG离子通道蛋白,4个A亚单元(A1～A4)和2个B亚单元(B1,B3).CNG离子通道是由2个或3个不同的亚单元组成的异四聚体复合物,是Ca2+进入细胞内的主要通道之一.CNG离子通道的活性可被Ca2+ /CaM及磷酸化/去磷酸化作用所调节,从而改变细胞内钙离子浓度,触发一系列生理效应.近年来CNG离子通道的研究进展神速,成为生命科学的一个热点领域.本文对CNG离子通道的结构、功能及活性调节机制进行了综述.     

从单（离子）通道记录的出现看单离子通道的涵义

从单（离子）通道记录的出现看单离子通道的涵义裴真明（中国科学院上海植物生理研究所,２０００３２）离子通道普存在于动植物细胞的各种膜上,离子通道和膜电位、动作电位、离子进出细胞及细胞的渗透调节等有关,所以近年来国内不仅对动物细胞的离子通道的研究重视,对...     

血管内皮细胞的Cl-通道--电特性和有关细胞功能

内皮细胞在心血管系统具有重要功能,除通过分泌内皮舒张因子－－一氧化氮（ＮＯ）及收缩性物质内皮素等控制血管平滑肌张力外,并能调节血管通透性。近年来发现内皮细胞上的Ｃ１＾－通道能调节细胞体积和细胞膜电位的稳定性。通过离子通道调控膜电位一机理,能较好理解血管内皮的功能,并可望由此开拓新型血管药物。本文综述了内皮细胞的Ｃ１＾－通道的电生理特性、类别,并探讨该通道调控细胞体积,ＮＯ的分泌及调控细胞膜电位的可     

蛇毒富含半胱氨酸分泌蛋白

富含半胱氨酸分泌蛋白(cystein-rich secretory protein, CRISP)家族包括众多不同起源的蛋白质,其大部分成员功能未知.近来研究表明,CRISP也是蛇毒中进化上十分保守的成分,已有多种蛇毒CRISP的晶体结构被解析.蛇毒CRISP可阻断Ca2 通道、K 通道及环核苷酸门控通道,因此是研究离子通道的潜在工具.本文综述近年来蛇毒CRISP结构和功能等方面的研究.     

血管内皮细胞容量激活的氯通道

氯通道是血管内皮细胞上主要的离子通道,容量激活的氯通道是其中一种主要类型并广为研究。已经主宰容量激活的氯通道在维持静息膜电位,调节细胞内钙、ｐＨ值,影响细胞增殖和分化中起着重要的作用。本文综述了血管内皮细胞容量激活氯通道的基本电生理及分子生物学特性,并初步探讨该通道的调节机制。     

大鼠海马CA1区锥体细胞上一种 Ca2+依赖性KATP通道

KATP通道在细胞的新陈代谢与膜兴奋性的耦联中起重要作用.采用膜片钳的内面向外式记录方法,在成年大鼠海马CA1区锥体细胞上记录到一种被胞浆侧ATP和甲糖宁(tolbutamide,一种KATP通道阻断剂)抑制的Ca2+依赖性钾离子通道.在细胞膜内外的K+浓度均为140 mmol/L时,通道的电导为(204±21) pS,翻转电位为(3.57±1.13) mV,通道无整流性.通道开放概率及ATP对通道的抑制作用均呈现电压依赖性.该KATP通道与以往报道的"经典"KATP通道有显著不同,其活动受膜电位、胞内Ca2+和ATP三重调节,表明这是一种新型的KATP通道.上述结果表明在海马神经元上至少有两种性质不同的KATP通道,提示神经元可能通过不同性质的KATP通道感受细胞内的代谢状态,进而调节细胞膜的兴奋性.     

神经冲动的发生机制

轴突兴奋伴有轴突膜电位变动。这种变动的发生基础是轴突膜分子运动、通道活动和离子运动等过程的相继发展。本文侧重介绍其中近年来有关离子通道的工作,兼及先前的离子理论和新近的分子观点。     

Charybdotoxin-sensitive, Ca(2+)-dependent membrane potential changes are not involved in human T or B cell activation and proliferation.

The involvement of ion channels in B and T lymphocyte activation is supported by many reports of changes in ion fluxes and membrane potential after mitogen binding. Human T and B lymphocytes demonstrate an early and transient hyperpolarization after ligand binding. Inasmuch as the change in membrane potential is dependent on elevation of free cytosolic calcium, the hyperpolarization is presumably through opening of Ca(2+)-stimulated K+ channels. We have used charybdotoxin, a known inhibitor of Ca(2+)-dependent K+ channels, to study the role of these channels in lymphocyte activation and mitogenesis. We demonstrate that charybdotoxin inhibits the ligand-induced transient membrane hyperpolarization in B and T cells in a dose-dependent fashion, without affecting changes in cytosolic Ca2+. However, blockade of the Ca(2+)-activated K+ channel is not associated with changes in cell-cycle gene activation, IL-2 production, IL-2R expression or B and T cell mitogenesis. These results imply that membrane potential changes secondary to the ligand-dependent opening of Ca(2+)-activated K+ channels are not involved in B and T lymphocyte activation and mitogenesis.     

Phosphatidylinositol-3 phosphatase myotubularin-related protein 6 negatively regulates CD4 T cells

Intracellular Ca2+ levels rapidly rise following cross-linking of the T-cell receptor (TCR) and function as a critical intracellular second messenger in T-cell activation. It has been relatively under appreciated that K+ channels play an important role in Ca2+ influx into T lymphocytes by helping to maintain a negative membrane potential which provides an electrochemical gradient to drive Ca2+ influx. Here we show that the Ca2+-activated K+ channel, KCa3.1, which is critical for Ca2+ influx in reactivated naive T cells and central memory T cells, requires phosphatidylinositol-3 phosphatase [PI(3)P] for activation and is inhibited by the PI(3)P phosphatase myotubularin-related protein 6 (MTMR6). Moreover, by inhibiting KCa3.1, MTMR6 functions as a negative regulator of Ca2+ influx and proliferation of reactivated human CD4 T cells. These findings point to a new and unexpected role for PI(3)P and the PI(3)P phosphatase MTMR6 in the regulation of Ca2+ influx in activated CD4 T cells and suggest that MTMR6 plays a critical role in setting a minimum threshold for a stimulus to activate a T cell.     

Different expression patterns of TRP genes in murine B and T lymphocytes

A prolonged increase in the intracellular calcium concentration ([Ca2+]i) is essential for lymphocyte activation that includes cell proliferation and differentiation. This increase in [Ca2+]i results from Ca2+ release from the intracellular store and the subsequent Ca2+ influx from the extracellular environment via calcium channels located on the plasma membrane. Although transient receptor potential (TRP) channels have been reported to play important roles in the [Ca2+]i increase in lymphocytes, the function of these channels in lymphocyte activation remains unknown. Here, we report the comprehensive expression profile of TRP channel gene families including TRPC, TRPV, and TRPM in the murine immune system. RT-PCR analysis revealed different expression patterns of the TRP channel genes in B and T lymphocytes isolated from the spleen. Therefore, our results provide an appropriate reference of TRP gene expression in murine lymphocytes.     

Plasma membrane ion channels in suicidal cell death

The machinery leading to apoptosis includes altered activity of ion channels. The channels contribute to apoptotic cell shrinkage and modify intracellular ion composition. Cl(-) channels allow the exit of Cl(-), osmolytes and HCO(3)(-) leading to cell shrinkage and cytosolic acidification. K(+) exit through K(+) channels contributes to cell shrinkage and decreases intracellular K(+) concentration, which in turn favours apoptotic cell death. K(+) channel activity further determines the cell membrane potential, a driving force for Ca(2+) entry through Ca(2+) channels. Ca(2+) may enter through unselective cation channels. An increase of cytosolic Ca(2+) may stimulate several enzymes executing apoptosis. Specific ion channel blockers may either promote or counteract suicidal cell death. The present brief review addresses the role of ion channels in the regulation of suicidal cell death with special emphasis on the role of channels in CD95 induced apoptosis of lymphocytes and suicidal death of erythrocytes or eryptosis.     

Abnormal regulation of ion channels in cystic fibrosis epithelia.

Cystic fibrosis (CF), the most common lethal genetic disease in Caucasians, is characterized by defective electrolyte transport in several epithelia. In sweat duct, pancreatic, intestinal, and airway epithelia, abnormalities in transepithelial ion transport may account for the manifestations of the disease. A Cl- impermeable apical cell membrane is a common feature in these CF epithelia. The rate of transepithelial Cl- transport is controlled in part by hormonally regulated apical membrane Cl- channels; in CF epithelia, Cl- channels are present but their regulation is defective. Most regulation studies have focused on an outwardly rectifying Cl- channel, although other channels may be involved in Cl- secretion. Phosphorylation of Cl- channels or associated regulatory proteins by cAMP-dependent protein kinase or by protein kinase C (at a low internal [Ca2+]) in excised patches of membrane activates Cl- channels in normal cells but not in CF cells. Phosphorylation with protein kinase C at a high internal [Ca2+] in excised patches of membrane inactivates the channel; such inactivation is normal in CF cells. Cl- channels can also be activated by other maneuvers including an increase in the cytosolic [Ca2+], sustained membrane depolarization, an increase in temperature, proteolysis, and changes in osmolarity; the response to such maneuvers is not defective in CF. In addition to the Cl- channel abnormalities, Na+ absorption is increased in CF epithelia. It is not certain whether the increased rate of Na+ absorption results from an increase in the number of cation channels or an alteration of their kinetics. The relation of these ion channel abnormalities to the CF gene product is unknown, but an understanding of the function of the protein product and its defective function in CF should yield important new insights into the pathogenesis and potential therapy of this disease.     

Cell volume and the regulation of apoptotic cell death

Apoptosis is a physiological mechanism allowing for the removal of abundant or potentially harmful cells. The hallmarks of apoptosis include degradation of cellular DNA, exposure of phosphatidylserine at the outer leaflet of the cell membrane and cell shrinkage. Phosphatidylserine exposure favours adhesion to macrophages with subsequent phagocytosis of the shrunken apoptotic particles. The interaction of cell volume regulatory mechanisms and apoptosis is illustrated in two different model systems, i.e. (a) lymphocyte apoptosis following stimulation of CD95 receptor and (b) erythrocyte apoptosis upon cell shrinkage. (a) Triggering of CD95 in Jurkat T lymphocytes is paralleled by activation of cell volume regulatory Cl- channels, inhibition of the Na+/H+ exchanger and osmolyte release. The latter coincides with cell shrinkage, DNA fragmentation and phosphatidylserine exposure. CD95 stimulation leads to early inhibition of the voltage gated K+ channel Kv1.3, which may contribute to the inhibition of the Ca2+ release activated Ca2+ channel I(CRAC). (b) Osmotic shock of erythrocytes activates a cell volume regulatory cation conductance allowing the entry not only of Na+ but of Ca2+ as well. Increased cytosolic Ca2+ stimulates a scramblase which disrupts the phosphatidylserine asymmetry of the cell membrane, leading to phosphatidylserine exposure. The cation conductance is further activated by oxidative stress and energy depletion and inhibited by Cl-. Shrinkage of erythrocytes stimulates in addition a sphingomyelinase with subsequent formation of ceramide which potentiates the effect of cytosolic Ca2+ on phosphatidylserine. In conclusion, cell volume-sensitive mechanisms participate in the triggering of apoptosis following receptor stimulation or cell injury.     

Evidence for localized calcium mobilization and influx in single rat gonadotropes.

Dynamic video-imaging microscopy was used to investigate the spatial and temporal nature of Ca2+ mobilization and Ca2+ influx in acutely dissociated, fura-2-loaded, rat gonadotropes. Addition of luteinizing hormone-releasing hormone (LHRH) to an isolated gonadotrope stimulated a wave of Ca2+ originating from a specific locus of the cell. This probably reflects Ca2+ mobilization from an intracellular store, since this response was unaffected by the removal of extracellular Ca2+. Application of the dihydropyridine-sensitive Ca2+ channel agonist Bay K 8644 (Bay K) stimulated a rise in cytosolic free Ca2+ concentration in the rat gonadotrope. This response was blocked by the removal of extracellular Ca2+ and probably reflects the influx of Ca2+ across the cell membrane. High speed (30 frames.s-1) imaging of the Bay K-induced Ca2+ influx revealed a wave of Ca2+ originating from a localized part of the cell membrane, which, in general, was spatially distinct from the LHRH-induced Ca2+ wave produced in the same cell. This suggests that Ca2+ channels in the cell membrane may be clustered in a specific area of the cell membrane. The velocity of the LHRH-induced Ca2+ mobilization wave was faster (mean = 79 +/- 5 microns.s-1, n = 9) than the Bay K-induced Ca2+ influx wave (39 +/- 7 microns.s-1, n = 9) (p less than or equal to 0.01, Wilcoxon signed rank test) measured in the same cells. Thus, both Ca2+ mobilization from intracellular stores and Ca2+ influx through the cell membrane appear to be spatially localized in the rat gonadotrope. These findings may have important implications in the intracellular regulation of Ca(2+)-dependent cell functions such as hormone biosynthesis and secretion.     

Increased anion permeability during volume regulation in human lymphocytes

Peripheral blood lymphocytes (p.b.ls) readjust their volumes after swelling in hypotonic media. An essential component of the regulatory response is an increase in K+ and Cl- permeability. No evidence was found for a tightly coupled co-transport of K+ and Cl-. The flux of either ion proceeds normally in the virtual absence of the transported counterion. Furthermore, alterations in membrane potential recorded during the phase of volume readjustment can be qualitatively accounted for by an increase in Cl- conductance. In tonsillar lymphocytes, a failure of the K+-permeability is nevertheless increased upon swelling. This further suggests that K+ and Cl- are transported during volume regulation through independent pathways. Cytoplasmic free Ca2+ appears to be involved in regulatory volume decrease. K+ and Cl-. Moreover, swelling and shrinking can be induced in isotonic K+-rich and K+-free media, respectively, by the Ca2+ ionophore. The ion flux and volume changes produced by either swelling or internal Ca2+ can be inhibited by similar concentrations of quinine and phenothiazines. The inhibitory activity of the latter drugs, which are powerful antagonists of calmodulin, suggests the participation of this Ca2+-regulator protein in volume regulation.