酸敏感离子通道与脑梗死

急性脑梗死约占全部脑卒中的70%,病死率和致残率高,且极易复发。但目前针对急性脑梗死在时间窗内溶栓、抗凝等治疗手段不能从根本上切实有效地修复受损脑组织,且伴有出血等风险。寻找脑梗死形成发展的原因并予以治疗迫在眉睫。酸中毒是引起缺血性脑损伤的重要机制。大量实验研究表明,酸中毒能加重神经元的缺血性损伤,且其梗死面积与酸中毒的程度直接相关。但缺血产生的酸中毒如何引起神经元损伤的确切机制尚不明确。最近研究发现酸中毒能激活一种在中枢及周围神经中广泛存在的膜通道,即酸敏感离子通道,它对Ca^2＋通透,能引起细胞内Ca^2＋超载,同时能激活胞内酶引起细胞内蛋白质、脂类及核酸的降解,加重缺血后脑损伤。本文就酸敏感离子通道1a与脑梗死做一综述。     

酸中毒和ASIC1a在复发性癫痫引起的树突棘重塑中的作用

复发性癫痫诱导慢性树突棘重塑对癫痫发生、终止和长期认知变化很关键,但是调控树突棘重塑的机制并不十分清楚。研究表明,癫痫发作时细胞外[H+]i增加导致组织酸中毒,激活酸敏感离子通道(acid-sensing ion channels,ASICs),引起慢性树突棘重塑。现总结酸中毒和酸敏感离子通道亚型ASIC1a在复发性癫痫引起的树突棘重塑中的作用,重点分析了酸中毒过程的时空变化对痫样放电和树突棘重塑可能的影响,以及酸中毒与ASIC1a在兴奋性和抑制性神经元的功能表达之间的关系,认为ASIC1a可能通过不同机制介导酸中毒在癫痫发生和持续阶段对树突棘的影响。未来研究需要进一步探索癫痫引起的慢性神经元结构和功能改变,阐明酸中毒和ASIC1a在癫痫及其引起的树突棘缺失中的作用。     

大鼠脊髓背角神经元中酸敏感离子通道的特性和功能研究

酸敏感离子通道（ASICs）是一类能被细胞外酸所激活的配体门控离子通道。本文综合报道大鼠脊髓背角神经元中ASICs的亚基组成及其功能性调节：（1）脊髓背角主要表达ASIC1a、ASIC2a和ASIC2b,但不表达ASIC1b和ASIC3;（2）在脊髓背角神经元中酸诱导电流可能由ASIC1a同聚体通道所介导;（3）胞外痛觉信号如实验性缺血和神经肽FMRF可以通过不同的机制增强脊髓背角神经元酸诱导电流;（4）炎症痛可以上调脊髓背角ASICs在转录和蛋白水平的表达。上述各点提示,在生理或病理情况下脊髓背角ASICs对脊髓水平的感觉信息传递特别是痛觉的传导可能发挥着重要作用。     

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。     

高血糖加重脑缺血损伤机制的研究现状

脑缺血是引起人类死亡的一个重要原因,由于其发病的分子机制十分复杂,各种因子作用相互影响,且多数因子的作用同时存在损伤和保护两种机制,使得脑缺血的研究充满了困难。目前众多研究都证实高血糖对缺血脑组织有损害作用,并可能导致局部或广泛缺血后预后更差。本文依据近几年的实验,重点阐述了五种最新的高血糖加重脑缺血过程和预后损伤的机制假说,包括高血糖通过引起过量谷氨酸释放导致的Ca2^＋大量内流造成损伤、高血糖状态下造成氧化应激从而产生各种自由基对神经元造成损伤、炎症因子相关的损伤、高血糖相关的血液灌流的减少以及高血糖造成脑内酸中毒从而引起损伤。期望这些对机制的探讨能够上加深广大医药研究人员对高血糖加重脑缺血损伤的认识,帮助找到新的药物作用靶点和治疗手段,启发新的研究思路。     

模拟高原低氧对大鼠肝细胞内质网Ca2+泵的影响

缺血、缺氧及细胞毒素都能使细胞内Ca2+浓度升高,Ca2+积累,导致细胞Ca2+代谢紊乱,引起细胞损伤和死亡.细胞质内Ca2+浓度升高通常是由于细胞内非线粒体Ca2+储存库内质网释放Ca2+所致.本实验中作者观察了不同时间不同程度模拟高原低氧条件下大鼠肝细胞内质网(endoplasmic reticulum,ER)Ca2+泵功能的变化,以了解低氧对Ca2+泵的影响.     

酸敏感离子通道在缺血性脑卒中作用的研究进展

酸敏感离子通道(acid-sensing ion channels,ASICs)属于上皮钠通道/退变素超家族中的一员,是一类质子(H~+)激活对阳离子选择性通透的非电压依赖的配体门控性离子通道。ASICs广泛分布于哺乳动物的神经系统,参与体内包括疼痛、学习、记忆、突触传递和可塑性调节等在内的多种生理和病理过程。近年来研究显示ASICs参与脑缺血神经元损伤过程,可能作为治疗缺血性脑卒中的新靶标。本文就目前ASICs在脑缺血神经元损伤过程的中作用的研究进展进行了综述。     

靶向酸敏感离子通道的神经保护:酸毒性损伤机制的重新审视

生理水平的质子在生物体内分布广泛,具有重要的生理功能。在特定的病理条件下,正常的酸碱平衡被破坏,导致质子大量生成和累积,产生对机体有害的酸毒(acidotoxicity)。组织酸化是多种神经系统疾病(如缺血性中风、多发性硬化症以及亨廷顿舞蹈症等)的共同病理特征,也是致这些疾病神经损伤的原因之一。质子可直接激活酸敏感离子通道(acid-sensing ion channel,ASIC),介导组织酸化相关的生理和病理功能,例如,缺血性神经损伤。一直以来,ASIC引起酸毒性神经损伤被认为主要依赖于通道介导的细胞内钙离子升高。然而,本研究组新近的研究表明ASIC1a亚型通道能够通过激活受体相互作用蛋白1(receptor-interacting protein 1,RIP1),介导不依赖于通道离子通透功能的细胞程序性坏死。另外,亚细胞定位研究发现,除了在神经元膜表面,ASIC1a还可以定位在线粒体内膜上,通过调控线粒体通透性转变(mitochondrial permeability transition,MPT)过程,在缺血性神经损伤中发挥重要作用。这些进展使人们对于ASIC介导神经元死亡的机制有了新的认识。     

膜超极化激活离子通道及其靶向抗癫痫药物研究进展

癫痫是一种较为常见的神经系统疾病,主要以大量神经元同步异常放电为特征。目前普遍认为,神经元或神经网络兴奋性和抑制性 电信号传输的失衡,是癫痫发病的最根本原因。现有的抗癫痫药物主要以钠离子通道、钙离子通道、钾离子通道、谷氨酸受体和γ-氨基丁 酸离子通道为靶点,但接受这些药物治疗后,仍有近1/3的病人无法控制癫痫发作。因此,抗癫痫药物的研发亟需新靶点和新思路。许多 研究证据表明,膜超极化激活离子通道的基因突变可以导致遗传型癫痫的发作,且在脑部损伤后,膜超极化激活离子通道会发生表达水平、 通道生物物理学性质及通道亚基构成的改变,从而增加神经元和神经网络兴奋性,促使癫痫发病。故近年来,膜超极化激活离子通道及其 靶向抗癫痫药物研究引起人们广泛关注。综述膜超极化激活离子通道与癫痫发病之间的关系,并探讨以膜超极化激活离子通道为靶点进行 抗癫痫药物开发和治疗的可行性。     

TRPC通道对PC12细胞缺氧缺糖再灌注后氧化损伤的保护作用

瞬时受体电位C通道(transient receptor potential canonical,TRPC)属于瞬时受体电位（TRP）离子通道家族成员之一,与Ca2+ 调控及氧化应激关系密切．然而,TRPC通道在缺血缺氧性脑损伤中的作用仍有争议．本实验采用MTT法、台盼蓝排斥实验、LDH漏出实验联合Annexin/PI染色流式分析等显示,当采用通道阻断剂-SKF96365特异阻断TRPC通道时,PC12细胞对缺氧缺糖再灌注（oxygen-glucose deprivation／reperfusion,OGD-R）引起的损伤变得更敏感,细胞凋亡增加．尽管同时采用SKF96365、NMDA受体、AMPA受体和L-型钙通道阻断剂可引起细胞损伤和死亡减弱,但仍呈现明显的SKF96365浓度依懒性,提示TRPC通道参与细胞对缺氧缺糖再灌注耐受的调节,具有保护作用．钙指示剂Fluo-3AM荧光标记结合激光共聚焦显微镜分析显示,SKF96365可明显降低缺氧缺糖再灌注后细胞内的Ca2+浓度．总之,实验结果提示,TRPC通道对缺氧缺糖再灌注引起的细胞损伤和凋亡具有保护作用,其机制可能涉及TRPC通道对细胞内钙浓度的调节,详尽机制有待进一步研究．     

Na(+)/Ca(2+) exchanger 2 is neuroprotective by exporting Ca(2+) during a transient focal cerebral ischemia in the mouse

Na(+)/Ca(2+) exchanger (NCX), by mediating Na(+) and Ca(2+) fluxes bi-directionally, assumes a role in controlling the Ca(2+) homeostasis in the ischemic brain. It has been suggested that the three isoforms of NCX (NCX1, 2 and 3) may be differentially involved in permanent cerebral ischemia. However, the role of NCX2 has not been defined in ischemic reperfusion injury after a transient focal cerebral ischemia. Furthermore, it is not known whether NCX2 imports or exports intracellular Ca(2+) ([Ca(2+)](i)) following ischemia and reperfusion. To define the role of NCX2 in ischemia and reperfusion, we examined mice lacking NCX2, in vivo and in vitro. After an in vitro ischemia, a significantly slower recovery in population spike amplitudes, a sustained elevation of [Ca(2+)](i) and an increased membrane depolarization were developed in the NCX2-deficient hippocampus. Moreover, a transient focal cerebral ischemia in vivo produced a larger infarction and more cell death in the NCX2-deficient mouse brain. In particular, in the wild type brain, NCX2-expressing neurons were largely spared from cell death after ischemia. Our results suggest that NCX2 exports Ca(2+) in ischemia and thus protects neuronal cells from death by reducing [Ca(2+)](i) in the adult mouse brain.     

Effects of cervical-lymphatic blockade on brain edema and infarction volume in cerebral ischemic rats

To observe the effects of cervical-lymphatic blockade (CLB) on brain edema and infarction volume of ischemic (MCAO) rat, we examined changes in cerebral water content, Ca2+ and glutamate concentrations, cerebral infarction volume and mRNA expression levels of N-methyl-D-aspartame receptor 1 (NMDA receptor 1) in the ischemic (left) hemisphere. The present results demonstrated that all the above indices in rats with middle cerebral artery occlusion plus cervical lymphatic blockade (MCAO+CLB) were markedly higher than those with only middle cerebral artery occlusion (MCAO) at different time points. These results indicated [corrected] that CLB can aggravate cerebral ischemia by increasing brain edema and infarction volume.     

Cleavage of the plasma membrane Na+/Ca2+ exchanger in excitotoxicity

In brain ischemia, gating of postsynaptic glutamate receptors and other membrane channels triggers intracellular Ca2+ overload and cell death. In excitotoxic settings, the initial Ca2+ influx through glutamate receptors is followed by a second uncontrolled Ca2+ increase that leads to neuronal demise. Here we report that the major plasma membrane Ca2+ extruding system, the Na+/Ca2+ exchanger (NCX), is cleaved during brain ischemia and in neurons undergoing excitotoxicity. Inhibition of Ca2+-activated proteases (calpains) by overexpressing their endogenous inhibitor protein, calpastatin or the expression of an NCX isoform not cleaved by calpains, prevented Ca2+ overload and rescued neurons from excitotoxic death. Conversely, down-regulation of NCX by siRNA compromised neuronal Ca2+ handling, transforming the Ca2+ transient elicited by non-excitotoxic glutamate concentrations into a lethal Ca2+overload. Thus, proteolytic inactivation of NCX-driven neuronal Ca2+ extrusion is responsible for the delayed excitotoxic Ca2+ deregulation and neuronal death.     

Nimodipine inhibits calcium-independent nitric oxide synthase activity in transient focal cerebral ischemia rats and cultured mouse astroglial cells

The effect of nimodipine on nitric oxide synthase (NOS) activities in brains in transient focal cerebral ischemia rats, in cultured mouse neurons and astroglial cells and bovine brain capillary endothelial cells (BCECs) was investigated. The administration of nimodipine (3 mg.kg(-1), p.o., twice a day, for 3 days) before middle cerebral artery (MCA) occlusion significantly reduced infarct size, decreased nitrite/nitrate (NOx) content and inhibited Ca2+-independent NOS activity in the infarct area. Nimodipine inhibited the Ca2+-independent NOS activity induced by lipopolysaccharide (LPS) + tumor necrosis factor alpha (TNF alpha) in mouse astroglial cells with an IC50 value of 0.036+/-0.003 mM and Ca2+-dependent NOS activity in mouse neurons with an IC50 value of 0.047+/-0.003 mM, but did not affect Ca2+-dependent NOS activity in BCECs. The inhibition of Ca2+-independent NOS activity by nimodipine in astroglial cells was competitive with respect to L-arginine. Nimodipine also inhibited the induction of Ca2+-independent NOS activity in vitro. These results suggest that nimodipine in addition to its cerebral vasodilating effect may protect brain from ischemic neuronal damage through modifying NOS activity.     

Glial perspectives of metabolic states during cerebral hypoxia--calcium regulation and metabolic energy

Cooperation between astrocytes and neurons is a unique interaction between two highly specialized cell types of the brain. Therefore, lack of nutrient supply during ischemia requires tight coordination of metabolism between astrocytes and neurons to keep the brain functions intact. To understand the impact of energy limitation on astrocytes, the functions of astrocytes have to be considered: (i) supplementation of neuronal cells, (ii) modulation of the extracellular milieu, mainly of the glutamate level, and (iii) elimination of reactive oxygen species (ROS). In cultured astrocytes and neurons inhibition of oxidative phosphorylation, using rotenone, was tested. Interestingly, this had only a negligible effect on Ca2+ homeostasis in astrocytes, even in combination with a severe glutamate stress. In contrast, in neurons glutamate in the presence of rotenone induced Ca2+ deregulation. Ca2+ homeostasis is very critical for cell survival. A massive and prolonged Ca2+ rise will lead to deregulation of many processes in such a way that the cells affected can hardly survive. Ca2+ homeostasis depends on the energy-consuming processes, which maintain the steep gradient between intracellular and extracellular Ca2+ concentration. Deprivation of oxygen and glucose during ischemia leads to a depletion of ATP in the brain, due to inhibited glycolytic and mitochondrial activity, whereas energy-consuming processes like ion pumps drain the ATP pools. On the other hand, specific mechanisms can protect brain structures against the massive insult of ischemia. Glycogen, stored in astrocytes, can maintain both neurons and astrocytes alive during short limitation of oxygen and glucose. Moreover, astrocytes can fuel ATP generation by providing lactate for neurons.     

The antioxidant prevention of disorders in calcium ion metabolism under the action of glutamate on the synaptosomes of the rat cerebral cortex]

An increase of intracellular calcium ion concentration and of the 45Ca2+ entry, a decrease in Na+,K(+)-ATPase activity, and activation of Na+/Ca2+ exchange were shown to be initiated by glutamate in the rat brain cortex synaptosomes. These effects could be prevented with antagonists and blocking agents of the NMDA receptors. Pre-incubation of the synaptosomes with alpha-tocopherol, superoxide dismutase, and ganglioside GM1 was shown to normalise [45Ca2+], the rate of 45Ca2+ entry, and the activity of Na+,K(+)-ATPase in the synaptosomes. The data obtained suggest that calcium ions entering the brain cortex neurones via the NMDA receptors in presence of excessive glutamate, trigger activation of free radical reactions damaging the neurones in ischemia, cerebral lesions, and other pathological conditions.     

Neuroprotective effect of dauricine in cortical neuron culture exposed to hypoxia and hypoglycemia: involvement of correcting perturbed calcium homeostasis

We have previously reported that dauricine protects brain tissues from focal cerebral ischemia. To corroborate this effect, neurotoxicity due to hypoxia and hypoglycemia was assessed in primary cultures of rat cortical neurons by using a trypan blue exclusion method. To further clarify the mechanism, the intracellular Ca2+ concentration ([Ca2+]i) and mitochondrial membrane potential (Deltapsim) of dissociated rat cortical cells were monitored by fura-2 fluorescence measurements and flow cytometry, respectively. The results showed that 1 and 10 micromol/L dauricine significantly enhanced neuronal survival during 4 h of hypoxia and hypoglycemia. Dauricine inhibited the increase in [Ca2+]i and decrease in Deltapsim induced by 30 min of hypoxia and hypoglycemia. When exploring the pathway, we found that 1 micromol/L dauricine inhibited the [Ca2+]i increase induced by 7.5 nmol/L thapsigargin in either the presence or absence of extracellular Ca2+ and by 1 mmol/L L-glutamate in the presence of extracellular Ca2+. These results suggest that dauricine prevents neuronal loss from ischemia in vitro, which is in accordance with our previous research in vivo. In addition, by inhibiting Ca2+ release from the endoplasmic reticulum and Ca2+ influx from the extracellular space, dauricine suppressed the increase in [Ca2+]i and, subsequently, the decrease in Deltapsim induced by hypoxia and hypoglycemia. This effect may underlie the mechanism of action of dauricine on cerebral ischemia.     

扩布性阻抑与脑缺血

研究表明,扩布性阻抑（ＳＤ）不仅与脑缺血,偏头痛,癫痫,颅脑创伤等疾患有关,而且可影响睡眠类型,觉醒等生理过程。本文重点对ＳＤ与脑缺血的关系进行了综述,订 叙述了以下几个问题：（１）ＳＤ的发现及研究简史;（２）完整脑内的ＳＤ;（３）局灶性脑梗塞周围的ＳＤ。     

脑梗死后海马神经元β—APP及其产物与ApoE的表达

目的：应用常规HE染色和免疫组织化学染色方法,观察人脑梗死后海马CA1区和CA3区神经元中β-APP、Aβ1-40、Aβ1-42及ApoE的表达,探讨它们表达变化的时间规律,以期对临床治疗提供可靠的实验资料。方法：分脑缺血组和对照组,脑缺血组按缺血时间分为缺血2h-6h组、7h-24h组、25h-48h组、49h-72h组．73h-96h组、97h-144h组和145h-168h组。采用HE染色方法观察神经细胞损伤情况;免疫组织化学染色检测β-APP、Aβ1-40、Aβ1-42与ApoE在尸检脑标本海马CA1区、CA3区神经元的表达,在显微镜下对免疫组织化学染色阳性细胞计数,实验结果应用SPSS12．0统计软件进行分析。结果：与对照组相比,Aβ1-40的表达在缺血2h后明显增加,73h-96h达高峰,以后有所回落,但仍高于对照组;β-APP在缺血2h-6h表达呈峰值,49h-96h呈现第二次高峰,96h以后下降,但仍高于对照组;于缺血24h后,β-APP和Aβ1-40的增加呈显著的正相关。缺血2h后．Aβ1-42表达开始增加,25h-48h达高峰;缺血6h后,ApoE表达开始增加,但97h-144h为高峰期。结论：人脑梗死后β-APP、Aβ1-40和Aβ1-42表达增加,它们可协同加重脑缺血性损伤;而ApoE脑保护作用可能增强。