环化二磷酸腺苷核糖及其钙动员的功能

环化二磷酸腺苷核糖（cyclic ADP-ribose,cADPR）是烟酰胺腺嘌呤二核苷酸(NAD⁺)的代谢产物,是新近发现的一种细胞内第二信使．在许多哺乳类和无脊椎动物细胞中,cADPR能引起胞内钙库释放钙离子,其可能机制是：cADPR受体结合cADPR,通过Ryanodine受体或类Ryanodine受体介导的钙通道使cADPR敏感的钙库释放钙离子,此外,一条由一氧化氮（NO）、环化鸟苷酸（cGMP）和cADPR组成的细胞内信号转导途径可能存在于许多细胞中．     

内质网上的蛋白质RCN2与STIM1-Orai1复合体相互作用

膜蛋白质Orail组成了一类被称为钙释放激活钙通道（CRAC）的离子通道,并且由相互作用的蛋白质STIM1作为其在内质网上的钙感受器．但是这类通道的调节机制还未研究透彻．通过串连亲和纯化STIM1-Orai1复合体,发现与之相互作用的内质网蛋白质RCN2．共聚焦显微术显示RCN2与STIM1在钙库排空前后完全共定位．对RCN2的EFhands结构突变体所作单细胞测钙,结果显示其对钙库操控通道电流特性有微弱影响．全内反射荧光显微术显示,RCN2以花环状围绕包围STIM1聚集堆,这提示RCN2在STIM1聚集中起到一种结构约束作用．     

β-肾上腺素受体调控心肌细胞兴奋收缩耦联的分子过程研究

兴奋收缩耦联是肌细胞兴奋期间由动作电位触发肌质网释放钙离子,从而导致收缩的过程。心肌细胞的兴奋收缩耦联是通过“钙致钙释放（Ca^2＋-induced Ca^2＋ release）的机制完成的。兴奋期间,细胞膜电位的去极化导致电压依赖性的L．型钙通道（LCC）开放,细胞外钙离子通过LCC流入细胞,激活了肌质网膜上称为ryanodine受体（RyR）的钙释放通道,后者从肌质网钙库中释放钙离子,使细胞质游离钙浓度迅速上升。细胞质钙浓度的升高一方面启动细胞收缩,另一方面激活了肌质网钙泵和细胞膜钠钙交换,二者分别将钙离子运回肌质网或细胞外,使细胞质钙浓度很快回落,从而完成了一次“钙瞬变（Ca^2＋ transient）”。钙瞬变在每个心动周期发生一次,是直接控制细胞收缩的细胞内信号。     

受体调节钙通道有三种机制

几乎所有的组织都有受体调节的钙通道,它们参与多种细胞功能,第二信使诱导的电压门控性钙通道开放是近年来提出的一种较完善的机制,以解释受体调节的钙电导变化。1,4,5-三磷酸肌醇(InsP_3)作为第二信使,使细胞内贮存的钙释放到胞浆内,使细胞内钙浓度([Ca](?))升高,从而引起钙内流,也就是钙通道开放。这种机制已经在几个系统内得到证实,但是在乳腺细胞中却没有发现这种电压门控性钙通道,而乳腺细胞上肯定存在着受体调节的钙通道。最近 Kuno,Reuter 和 Irvine 分别提出了另外三种机制,解释受体介导的钙内流。     

钙池操纵的钙通道的调控机制

钙池操纵的钙通道（store—operated calciumchannel,SOC）系存在于细胞膜表面的一种新发现的钙通道,它是非兴奋性细胞Ca^2＋内流的主要通道。SOC的开启是由钙库耗竭所激发,然而,钙库耗竭如何开启SOC仍不十分清楚。文章综述了SOC开启调控机制的有关研究进展。     

STIM／SOCE通路参与细胞功能调控的研究进展

钙库操作性钙离子通道（store-operated calcium entry,SOCE）是介导胞外Ca^2＋进入细胞内的重要通道之一,其核心蛋白由位于内质网上的基质相互作用分子（stromalinteractionmolecule,STIM）和位于细胞膜上的Orai蛋白构成。目前研究发现,STIM蛋白存在STIM1和STIM2两种亚型,其主要功能略有不同。当内质网内钙库中Ca^2＋消耗之后,STIM蛋白通过其特殊的结构能够感受内质网内钙库中Ca^2＋浓度的变化,发生快速的转位和聚合化等激活反应,与质膜上的Orai蛋白偶联。实现SOCE通路的功能开放,引起Ca^2＋内流。当钙库中Ca^2＋得到补充之后,STIM蛋白与Orai蛋白缓慢解离即失活,通路关闭。目前对STIM蛋白结构的研究提示,通过其激活和失活机制不仅能够参与调节SOCE通路的开放与关闭,也参与对细胞内重要的细胞增殖、分化等功能活动调控。STIM蛋白可能成为治疗多种疾病的潜在的新靶点。     

受体调节的钙内流不存在秘密通道

某些物质与受体结合后,激活磷脂酶C,促进4,5-二磷酸磷脂酰肌醇水解成1,4,5-三磷酸肌醇(IP_3),引起内质网钙库的排空,即钙的动员,钙库的排空进而又可刺激外钙的内流。受体调节的钙内流主要受钙库的排空控制。实验表明,激素敏感的钙库处于排空状态时较易与细胞外     

阿片受体与离子通道

阿片主要影响钾通道和钙通道,三种亚型的阿片受体μ、δ、к激动剂都有开放钾通道和关闭钙通道的作用,也有许多文献报道阿片对钾通道具有双向作用,即低浓度（＜ｎＭ）关闭钾通道,呈现兴奋作用,而高浓度开放钾通道,呈现抑制作用．阿片对钙通道也具有双向作用,低浓度开放钙通道和升高细胞内钙,呈现兴奋作用,高浓度关闭钙通道和降低细胞内钙,呈现抑制作用．     

STIM和Orai在钙库操纵的钙内流途径及心脑血管疾病中的作用

钙库操纵的钙内流(SOCE)是调节钙离子(Ca2+)内流进入细胞最普遍的一种途径,它的通道称为钙库操纵的钙内流通道(SOC)。SOC存在于大多数非兴奋细胞和部分兴奋细胞上,近年来确定,STIM和Orai是组成SOC的两种主要蛋白质。本文就近年来对SOCE途径的机制,STIM和Orai不同亚型的结构、功能及在心脑血管疾病中的作用作一综述。     

FK-506结合蛋白对钙释放通道的调控

细胞内自由钙作为一种重要的细胞信使广泛地参与细胞生理功能调控.胞内钙库(内质网系和肌浆网系)对调节细胞内自由钙水平起着重要的作用.钙库膜上的钙释放通道(ryanodine受体和三磷酸肌醇受体)受许多因素调控,其中之一就是新近研究得相当多的FK506结合蛋白.免疫抑制剂FK506能特异地结合钙库上一种分子质量为12 ku左右的蛋白,这种FK506结合蛋白与钙释放通道形成一种紧密连接的复合体,在正常生理情况下对钙释放通道起着十分重要的调控作用.     

Capacitative calcium entry channels

In the phospholipase C signaling system, Ca(2+) is mobilized from intracellular stores by an action of inositol 1,4,5-trisphosphate. The depletion of intracellular calcium stores activates a calcium entry mechanism at the plasma membrane called capacitative calcium entry. The signal for activating the entry is unknown but likely involves either the generation or release, or both, from the endoplasmic reticulum of some diffusible signal. Recent research has focused on mammalian homologues of the Drosophila TRP protein as potential candidates for capacitative calcium entry channels. This review summarizes current knowledge about the nature of capacitative calcium entry signals, as well as the potential role of mammalian TRP proteins as capacitative calcium entry channel molecules.     

Capacitative calcium entry mechanism in porcine oocytes

The presence of the capacitative Ca(2+) entry mechanism was investigated in porcine oocytes. In vitro-matured oocytes were treated with thapsigargin in Ca(2+)-free medium for 3 h to deplete intracellular calcium stores. After restoring extracellular calcium, a large calcium influx was measured by using the calcium indicator dye fura-2, indicating capacitative Ca(2+) entry. A similar divalent cation influx could also be detected with the Mn(2+)-quench technique after inositol 1,4,5-triphosphate-induced Ca(2+) release. In both cases, lanthanum, the Ca(2+) permeable channel inhibitor, completely blocked the influx caused by store depletion. Heterologous expression of Drosophila trp in porcine oocytes enhanced the thapsigargin-induced Ca(2+) influx. Polymerase chain reaction cloning using primers that were designed based on mouse and human trp sequences revealed that porcine oocytes contain a trp homologue. As in other cell types, the capacitative Ca(2+) entry mechanism might help in refilling the intracellular stores after the release of Ca(2+) from the stores. Further investigation is needed to determine whether the trp channel serves as the capacitative Ca(2+) entry pathway in porcine oocytes or is simply activated by the endogenous capacitative Ca(2+) entry mechanism and thus contributes to Ca(2+) influx.     

A role for voltage gated T-type calcium channels in mediating "capacitative" calcium entry?

Calcium entry through plasma membrane calcium channels is one of the most important cell signaling mechanism involved in such diverse functions as secretion, contraction and cell growth by regulating gene expression, proliferation and apoptosis. The identity of plasma membrane calcium channels, the main regulators of calcium entry, involved in cell proliferation has been thus extensively sought. Among these, a calcium entry pathway called capacitative calcium entry (CCE), activated by calcium store depletion, is particularly important in non-excitable cells. Though this capacitative calcium entry is generally supposed to occur through TRP channels there is some evidence that voltage-dependent T-type calcium channels may contribute to calcium entry after store depletion. Here we show that though mibefradil, a T-type calcium channel blocker, is able to reduce capacitative calcium entry induced by either thapsigargin or ATP, this was not mimicked by any other T-type calcium channel inhibitors even in cells overexpressing alpha(1H) T-type calcium channels, leading us to conclude that T-type calcium channels are not responsible for the capacitative calcium entry observed in different cancer cell lines. On the contrary, we show that the action of mibefradil on capacitative calcium entry is due to an action on store-operated calcium channels.     

Capacitative calcium entry: sensing the calcium stores

A long-standing mystery in the cell biology of calcium channel regulation is the nature of the signal linking intracellular calcium stores to plasma membrane capacitative calcium entry channels. An RNAi-based screen of selected Drosophila genes has revealed that a calcium-binding protein, stromal interaction molecule (STIM), plays an essential role in the activation of these channels and may be the long sought sensor of calcium store content.     

Capacitative calcium entry in the nervous system

Capacitative calcium entry is a process whereby the depletion of Ca(2+) from intracellular stores (likely endoplasmic or sarcoplasmic reticulum) activates plasma membrane Ca(2+) channels. Current research has focused on identification of capacitative calcium entry channels and the mechanism by which Ca(2+) store depletion activates the channels. Leading candidates for the channels are members of the transient receptor potential (TRP) superfamily, although no single gene or gene product has been definitively proven to mediate capacitative calcium entry. The mechanism for activation of the channels is not known; proposals fall into two general categories, either a diffusible signal released from the Ca(2+) stores when their Ca(2+) levels become depleted, or a more direct protein-protein interaction between constituents of the endoplasmic reticulum and the plasma membrane channels. Capacitative calcium entry is a major mechanism for regulated Ca(2+) influx in non-excitable cells, but recent research has indicated that this pathway plays an important role in the function of neuronal cells, and may be important in a number of neuropathological conditions. This review will summarize some of these more recent findings regarding the role of capacitative calcium entry in normal and pathological processes in the nervous system.     

Cloning and functional expression of human short TRP7, a candidate protein for store-operated Ca2+ influx.

The regulation and control of plasma membrane Ca(2+) fluxes is critical for the initiation and maintenance of a variety of signal transduction cascades. Recently, the study of transient receptor potential channels (TRPs) has suggested that these proteins have an important role to play in mediating capacitative calcium entry. In this study, we have isolated a cDNA from human brain that encodes a novel transient receptor potential channel termed human TRP7 (hTRP7). hTRP7 is a member of the short TRP channel family and is 98% homologous to mouse TRP7 (mTRP7). At the mRNA level hTRP7 was widely expressed in tissues of the central nervous system, as well as some peripheral tissues such as pituitary gland and kidney. However, in contrast to mTRP7, which is highly expressed in heart and lung, hTRP7 was undetectable in these tissues. For functional analysis, we heterologously expressed hTRP7 cDNA in an human embryonic kidney cell line. In comparison with untransfected cells depletion of intracellular calcium stores in hTRP7-expressing cells, using either carbachol or thapsigargin, produced a marked increase in the subsequent level of Ca(2+) influx. This increased Ca(2+) entry was blocked by inhibitors of capacitative calcium entry such as La(3+) and Gd(3+). Furthermore, transient transfection of an hTRP7 antisense expression construct into cells expressing hTRP7 eliminated the augmented store-operated Ca(2+) entry. Our findings suggest that hTRP7 is a store-operated calcium channel, a finding in stark contrast to the mouse orthologue, mTRP7, which is reported to enhance Ca(2+) influx independently of store depletion, and suggests that human and mouse TRP7 channels may fulfil different physiological roles.     

Comparison of human TRPC3 channels in receptor-activated and store-operated modes. Differential sensitivity to channel blockers suggests fundamental differences in channel composition

Capacitative calcium entry or store-operated calcium entry in nonexcitable cells is a process whereby the activation of calcium influx across the plasma membrane is signaled by depletion of intracellular calcium stores. Transient receptor potential (TRP) proteins have been proposed as candidates for store-operated calcium channels. Human TRPC3 (hTRPC3), an extensively studied member of the TRP family, is activated through a phospholipase C-dependent mechanism, not by store depletion, when expressed in HEK293 cells. However, store depletion by thapsigargin is sufficient to activate hTRPC3 channels when expressed in DT40 avian B-lymphocytes. To gain further insights into the differences between hTRPC3 channels generated in these two expression systems and further understand the role of hTRPC3 in capacitative calcium entry, we examined the effect of two well characterized inhibitors of capacitative calcium entry, Gd3+ and 2-aminoethoxydiphenyl borane (2APB). We confirmed that in both DT40 cells and HEK293 cells, 1 microm Gd3+ or 30 microm 2APB completely blocked calcium entry due to receptor activation or store depletion. In HEK293 cells, 1 microm Gd3+ did not block receptor-activated hTRPC3-mediated cation entry, whereas 2APB had a partial (approximately 60%) inhibitory effect. Interestingly, store-operated hTRPC3-mediated cation entry in DT40 cells was also partially inhibited by 2APB, whereas 1 microm Gd3+ completely blocked store-operated hTRPC3 activity in these cells. Furthermore, the sensitivity of store-operated hTRPC3 channels to Gd3+ in DT40 cells was similar to the endogenous store-operated channels, with essentially 100% block of activity at concentrations as low as 0.1 microm. Finally, Gd3+ has a rapid inhibitory effect when added to fully developed hTRPC3-mediated calcium entry, suggesting a direct action of Gd3+ on hTRPC3 channels. The distinct action of these inhibitors on hTRPC3-mediated cation entry in these two cell types may result from their different modes of activation and may also reflect differences in basic channel structure.     

Mechanism of store-operated calcium entry

Activation of receptors coupled to the phospholipase C/IP₃ signalling pathway results in a rapid release of calcium from its intracellular stores, eventually leading to depletion of these stores. Calcium store depletion triggers an influx of extracellular calcium across the plasma membrane, a mechanism known as the store-operated calcium entry or capacitative calcium entry. Capacitative calcium current plays a key role in replenishing calcium stores and activating various physiological processes. Despite considerable efforts, very little is known about the molecular nature of the capacitative channel and the signalling pathway that activates it. This review summarizes our current knowledge about store operated calcium entry and suggests possible hypotheses for its mode of activation.     

Role ofDrosophila TRP in inositide-mediated Ca2+ entry

Inositol lipid signaling relies on an InsP₃-induced Ca²⁺ release from intracellular stores and on extracellular Ca²⁺ entry, which takes place when the Ca²⁺ stores become depleted of Ca²⁺. This interplay between Ca²⁺ release and Ca²⁺ entry has been termed capacitative Ca²⁺ entry and the inward current calcium release activated current (CRAC) to indicate gating of Ca²⁺ entry by Ca²⁺-store depletion. The signaling pathway and the gating mechanism of capacitative Ca²⁺ entry, however, are largely unknown and the molecular participants in this process have not been identified. In this article we review genetic, molecular, and functional studies of wild-type and mutantDrosophila photoreceptors, suggesting that thetransient receptor potential mutant (trp) is the first putative capacitative Ca²⁺ entry mutant. Furthermore, several lines of evidence suggest that thetrp gene product TRP is a candidate subunit of the plasma membrane channel that is activated by Ca²⁺ store depletion.