HCN通道在中枢神经系统的功能和调节机制研究进展

超极化激活环核苷酸门控(HCN)离子通道分布于机体多种组织中,尤其在兴奋性细胞(如心脏细胞和多种类型的神经元)中表达丰富,在控制心脏节律和维持细胞膜兴奋性等方面发挥重要功能。不同于经典的电压依赖性钠离子通道和钾离子通道,HCN通道在膜电位超极化时激活,诱发向内电流。近来的系列研究发现,HCN通道在神经系统中起着重要的作用,这与其特殊的电生理特性及其对细胞膜兴奋性的调节紧密关联。HCN通道受到细胞内外多种分子机制调节,使其在不同的生理病理条件下功能更加复杂。目前,HCN通道被认为是一个潜在的治疗慢性疼痛和多种脑疾病的新靶标。本文将重点围绕HCN通道在神经系统中的功能及其调节机制进行综述。     

M受体的研究进展

M受体是机体中最重要的受体之一，根据药理学分类可分为M1，M2，M3和M4 4种药理学亚,发子克隆技术可将其分为m1,m2,m3,m4和m5，其中M1，M2和M3分别对应于m1,m2和m3。各种亚型基本结构相似，主要差别在于胞浆内3环（i3环）的不同，这决定了它们功能的不同。m1，m3和m5结构功能相似，可激活PI系统和cAMP，m2和m4则可抑制腺苷酸环化酶系统。不同部位各种亚型的分布和功能也有所不同。M受体亚型的分布和功能及其活性药物对临床具有重要意义。     

KCNQ2/3钾通道电流特征及M_1受体的调节作用

目的观察KCNQ2/3通道电流特征及M1受体激活对该电流的调节作用。方法以CHO细胞作为表达体系,用脂质体共转染KCNQ2、KCNQ3钾离子通道及毒蕈碱型M1受体。全细胞膜片钳方法,观察KCNQ2/3电流特征,药理学阻断剂的作用及M1受体激活对电流的调节。结果KC-NQ2/3电流呈现慢激活、低阈值、非失活、电压依赖性的外向钾离子电流特点,其激活电压的阈值在-60 mV,半数激活电压值(-26.8±1.2)mV,其去活曲线可用双指数方程拟合,fτast约101 m s;sτlow约为309 m s。该电流对4-AP,Ba2+,TEA不敏感,L inop ird ine抑制KCNQ2/3电流IC50为(6.5±0.83)μmol.L-1。乙酰胆碱激活M1受体后会可逆性地抑制KCNQ2/3电流,其抑制的IC50为(0.7±0.05)μmol.L-1。结论KCNQ2/3通道作为神经细胞M通道的分子基础,其电流特征与M电流一致,L inop ird ine对其有较强阻断作用,神经递质乙酰胆碱通过激活M1受体明显抑制该通道电流。研究KCNQ2/3通道电流特征及受体调节规律,对于理解与中枢兴奋性有关的疾病如:惊厥、癫痫、阿尔采末病等发生机制有重要指导意义。     

细胞内pH对胆碱能受体介导的Kir3.1/3.4电流的调节

目的　研究细胞内pH对胆碱能受体介导的Kir3 1/3 4电流的调节作用。方法　应用AzideNa、KHCO3 和通过灌流直接降低细胞内 pH ,用双电极电压钳和膜片钳方法观察在蛙卵细胞中表达的Kir3 1/ 3 4钾离子通道电流的变化和M受体激活对Kir3 1/ 3 4电流调节的变化。结果　细胞内 pH降低能抑制Kir3 1/ 3 4的电流 ;Kir3 1/ 3 4对细胞内pH的敏感性介于另外两种Kir通道Kir2 1和Kir2 3之间 ,即这三种通道对细胞内 pH的敏感性依次为Kir2 3>Kir3 1/ 3 4 >Kir2 1;细胞内pH降低能够减弱M1受体激活对Kir3 1/ 3 4的抑制作用 ,加强M2 受体激活Kir3 1/ 3 4电流后的去敏作用。结论　在维持细胞静息电位方面起重要作用的Kir3 1/ 3 4通道在细胞内pH降低的情况下基础电流和M受体激活调节电流均发生了变化 ,这些变化在缺血缺氧引起的细胞 (如心肌细胞 )兴奋性改变中可能有重要的生理学意义     

脊髓背角M胆碱能和GABAB受体在糖尿病神经痛形成中的作用机制研究进展

脊髓背角作为中枢神经系统痛觉信息整合加工的重要部位,是接受和调控伤害性信息由外周向中枢传递的关键部位。背角浅层含有大量的谷氨酸能、胆碱能、GABA能及甘氨酸能神经元,这些神经元的轴突末梢及胞体上同时表达丰富的M胆碱能受体和GABAB受体,激活这些受体可调控兴奋性/抑制性神经递质的释放过程。而在糖尿病神经痛的形成过程中,     

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。     

靶向电压门控KCNQ/M钾通道的调节剂对神经精神疾病的潜在治疗作用

1980年David Brown博士首次发现了M型乙酰胆碱受体激动剂可以抑制一种钾通道电流,并将其命名为M型钾电流（IM）十八年后科学家们克隆了导致新生儿癫痫的KCNQ2和KCNQ3突变基因,并且证明KCNQ2和KCNQ3亚基异源组装介导M型钾通道电流。电压门控KCNQ2/3钾通道（亦称M通道）功能降低可导致神经元的过度兴奋,诱发癫痫及慢性疼痛。因此,研发激活KCNQ2/3通道功能的开放剂可用于治疗癫痫和疼痛等神经疾病。著名的KCNQ通道开放剂瑞替加滨retigabine（商品名Potiga）于2011年被美国食品与药品监督管理局批准治疗癫痫。我们最近参与研发了一类新型的KCNQ2/3特异性开放剂—吡唑并[1,5-a]嘧啶酮类化合物。在动物模型上,该开放剂具有抗癫痫和镇痛的效果。最近的研究工作提示,KCNQ通道开放剂还对抑郁症、焦虑症和精神分裂症等动物模型有效,而KCNQ通道抑制剂可以提高动物的学习与记忆能力。目前的研究进展提示,电压门控KCNQ/M通道是治疗神经精神类疾病的靶点,靶向该通道的调节剂对多种神经精神疾病具有潜在的治疗价值。     

M1胆碱受体激动剂治疗阿尔茨海默病的研究进展

阿尔茨海默病(Alzheimer disease，AD)是一种以胆碱能神经元进行性退变、老年斑和神经元缠结为病理特征的神经退行性疾病。尽管AD发病机制尚未阐明，但β淀粉样肽沉积和tau蛋白磷酸化与胆碱能神经退变的恶性循环(vicious cycle)无疑是造成AD的重要病理机制之一。大量研究表明胆碱能神经突触后膜的M1受体的数目在整个病程中变化不大，M1受体选择性激动剂不但可以直接补偿胆碱能的功能，而且可以调节β淀粉样前体蛋白代谢和降低tau蛋白的过度磷酸化，有助于打破这一恶性循环，改善AD的学习记忆功能并延缓病情的发展。因此M1胆碱受体激动剂被认为是最有前途的治疗AD药物之一。目前Xanomeline、Sabcomeline等具有相对选择性M1受体激动剂业已进入新药临床试验阶段。     

N和M胆碱能受体之间的相互调节

N和M胆碱能受体拥有同一种内源性配基ACh ,并且在多种组织中两种受体共存 ,两者之间存在着多种相互作用。如副交感神经节后N受体可通过刺激胆碱能神经纤维末梢释放ACh来调节组织中M受体的功能 ;而胆碱能神经元突触后N受体的活性也可被突触前膜上M和N的自受体通过反馈调控节前纤维ACh的释放来调节 ;另外 ,N受体被阻断或失敏后不同组织中M受体的功能会发生不同的变化 ,以将机体胆碱能神经系统维持在一个稳定状态     

谷氨酸神经细胞毒作用的新途径——谷氨酸/胱氨酸转运体介导机制

谷氨酸是中枢神经系统主要的兴奋性神经递质 ,与许多神经系统疾病有密切关系。谷氨酸除通过激活谷氨酸受体产生兴奋性神经毒性外 ,还可通过抑制细胞膜上谷氨酸 /胱氨酸转运体的功能产生细胞毒性作用 ,该作用以细胞内谷胱甘肽耗竭和活性氧成分升高为主要特征 ,被称为谷氨酸的氧化毒性 ,对许多神经系统疾病的治疗具有重要意义。     

A potassium channel, the M-channel, as a therapeutic target

Compounds that stimulate or inhibit M-channels (ie, voltage-gated potassium channels formed by KCNQ2, KCNQ3 and KCNQ5) have been evaluated in clinical trials for epilepsy, stroke and Alzheimer's disease. The importance of M-channel function in reducing neuronal excitability is underscored by the finding that KCNQ2/3 mutations causing mild reduction of M-channel activity are linked to neonatal epilepsy. M-channel openers decrease the hyperexcitability responsible for epileptic seizures, neuropathic pain and migraine. Conversely, M-channel blockers may enhance cognitive functions. The M-channel has thus emerged as a promising target for treating epilepsy, stroke, migraine, pain, dementia, anxiety and bipolar disorder.     

Cortical epileptic afterdischarges in immature rats are differently influenced by NMDA receptor antagonists

Linopirdine was developed as a cognitive enhancing molecule and demonstrated to specifically block the potassium current generated by the brain specific KCNQ2-KCNQ3 proteins (M-channel). In this study we investigated the relevance of [(3)H]linopirdine binding in rat brain extracts to the interaction with the M-channel proteins. Our results confirm the presence of a high affinity site for [(3)H]linopirdine in rat brain tissues (KD = 10 nM) but we also identified a high affinity binding site for [(3)H]linopirdine in rat liver tissues (KD = 9 nM). Competition experiments showed that [(3)H]linopirdine is displaced by unlabelled linopirdine with comparable affinities from its binding sites on rat brain and rat liver membranes. [(3)H]linopirdine was completely displaced by a set of cytochrome P450 (CYP450) ligands suggesting that [(3)H]linopirdine binding to rat brain and liver membranes is linked to CYP450 interaction. The testing of CYP450 ligands on the M-channel activity, using a Rb(+) efflux assay on cells expressing the KCNQ2-KCNQ3 proteins, demonstrated that [(3)H]linopirdine binding results cannot be correlated to M-channel inhibition. The results obtained in this study demonstrate that [(3)H]linopirdine binding to rat brain and rat liver membranes is representative for CYP450 interaction and not relevant for the binding to the M-channel proteins.     

Cognition enhancement strategies by ion channel modulation of neurotransmission

Relatively few effective therapies exist for the multitude of disorders that comprise dementia, a clinical syndrome manifested by impairments in cognition, language and memory. Treatment of Alzheimer s disease (AD), the most common cause of dementia, is a primary goal of research in cognitive enhancement. However, despite intense research, effective pharmacological interventions remain to be developed. The preponderance of pharmacological strategies which are being pursued in AD research attempt to relieve cognitive and memory deficits which are attributed to cholinergic dysfunction. This paper briefly reviews the status of other efforts that have in common the potential to enhance the use-dependent activity of multiple neurotransmitters system through the modulation of gated ion channels. Discussed are recent advances in the areas of: 1) g-aminobutyric acid subtype A receptor/benzodiazepine (GABAA/BZ) inverse agonists; 2) nicotinic acetylcholine receptor (nAChR) agonists; 3) serotonin subtype 3 receptor (5-HT3R) antagonists; and 4) potassium (K+) M-channel inhibitors.     

Is it possible to design rational treatments for the symptoms of Alzheimer's disease?

This paper reviews and discusses the evidence that the primary cause of the symptoms of Alzheimer's disease is a deficiency of acetylcholine in cerebral cortex and hippocampus. Data on other neurotransmitters in this disease are briefly reviewed. Possible means of treating acetylcholine deficiences are discussed.     

癫痫外科治疗的研究进展

癫痫是神经系统的常见病并且危害较大,其发病机制不甚明确.当前治疗癫痫的重要手段是抗癫痫药物(AEDs)的应用.在现代医学快速发展的背景下,近年来各种新型AEDs投入使用并取得了良好的效果.然而,仍有部分患者呈药物难治性,对于这部分患者可以采用手术治疗的方式来达到控制癫痫的效果.该文现就癫痫外科手术过程中术前必要的评估、术式的选择、手术预后的评估以及术后用药等几个方面综述如下.     

Update on novel antiepileptic drugs

Epilepsy is the most common serious neurological condition. Approximately 20% of patients with epilepsy are resistant to current antiepileptic drugs (AEDs), and newly licensed AEDs have not significantly changed the prognosis for this group. New AEDs are thus still needed to treat this refractory group. Although established AEDs have been very successful in treating epilepsy, they are associated with frequent adverse events, and newer AEDs with better side-effect profiles may eventually replace the older drugs as first-line therapy. There has, however, been caution in using new AEDs as first-line treatment because of questions of long-term safety and cost. As well as treating epilepsy, there is a need for drugs that prevent the development of epilepsy following, for example, head injury. None of the established AEDs has been shown to achieve this, but newer drugs have been found to be anti-epileptogenic in animal models. Whether this is so in the clinical situation has yet to be established. This is a potentially large under-investigated market. Although new AEDs have largely been developed through widespread screening in animal epilepsy models and the modification of existing compounds, there has been a growth in the rational development of AEDs. Drugs that increase brain g-aminobutyric acid (GABA) concentrations have now become well-established, and a new drug, tiagabine, that operates via this mechanism is shortly to be launched in a number of countries. Research has recently been concentrated on the development of drugs whose antiepileptic effect is mediated through glutamate receptors. Initial investigation of N-methyl-D-aspartate (NMDA) receptor antagonists in patients with epilepsy was disappointing, but drugs that act via non-NMDA glutamate receptors, and metabotropic glutamate receptors look promising.     

Neural KCNQ (Kv7) channels

KCNQ genes encode five Kv7 K⁺ channel subunits (Kv7.1–Kv7.5). Four of these (Kv7.2–Kv7.5) are expressed in the nervous system. Kv7.2 and Kv7.3 are the principal molecular components of the slow voltage-gated M-channel, which widely regulates neuronal excitability, although other subunits may contribute to M-like currents in some locations. M-channels are closed by receptors coupled to Gq such as M1 and M3 muscarinic receptors; this increases neuronal excitability and underlies some forms of cholinergic excitation. Muscarinic closure results from activation of phospholipase C and consequent hydrolysis and depletion of membrane phosphatidylinositol-4,5-bisphosphate, which is required for channel opening. Some effects of M-channel closure, determined from transmitter action, selective blocking drugs (linopirdine and XE991) and KCNQ2 gene disruption or manipulation, are as follows: (i) in sympathetic neurons: facilitation of repetitive discharges and conversion from phasic to tonic firing; (ii) in sensory nociceptive systems: facilitation of A-delta peripheral sensory fibre responses to noxious heat; and (iii) in hippocampal pyramidal neurons: facilitation of repetitive discharges, enhanced after-depolarization and burst-firing, and induction of spontaneous firing through a reduction of action potential threshold at the axon initial segment. Several drugs including flupirtine and retigabine enhance neural Kv7/M-channel activity, principally through a hyperpolarizing shift in their voltage gating. In consequence they reduce neural excitability and can inhibit nociceptive stimulation and transmission. Flupirtine is in use as a central analgesic; retigabine is under clinical trial as a broad-spectrum anticonvulsant and is an effective analgesic in animal models of chronic inflammatory and neuropathic pain.     

Brain nicotinic acetylcholine receptors: native subtypes and their relevance

Neuronal nicotinic acetylcholine receptors comprise a heterogeneous class of cationic channels that is present throughout the nervous system. These channels are involved both in physiological functions (including cognition, reward, motor activity and analgesia) and in pathological conditions such as Alzheimer's disease, Parkinson's disease, some forms of epilepsy, depression, autism and schizophrenia. They are also the targets of tobacco-smoking effects and addiction. Neuronal nicotinic acetylcholine receptors are pentamers of homomeric or heteromeric combinations of alpha (alpha2-alpha10) and beta (beta2-beta4) subunits, which have different pharmacological and biophysical properties and locations in the brain. The lack of subtype-specific ligands and the fact that many neuronal cells express multiple subtypes initially hampered the identification of the different native nicotinic acetylcholine receptor subtypes, but the increasing knowledge of subtype composition and roles will be of considerable interest for the development of new and clinically useful nicotinic acetylcholine receptor ligands.     

Is there a role for potassium channel openers in neuronal ion channel disorders?

Malfunction in ion channels, due to mutations in genes encoding channel proteins or the presence of autoantibodies, are increasing being implicated in causing disease conditions, termed channelopathies. Dysfunction of potassium (K(+)) channels has been associated with the pathophysiology of a number of neurological, as well as peripheral, disorders (e.g., episodic ataxia, epilepsy, neuromyotonia, Parkinson's disease, congenital deafness, long QT syndrome). K(+) channels, which demonstrate a high degree of diversity and ubiquity, are fundamental in the control of membrane depolarisation and cell excitability. A common feature of K(+) channelopathies is a reduction or loss of membrane potential repolarisation. The identification of K(+) channel subtype specific openers will allow the recovery of the mechanism(s) responsible for counteraction of uncontrolled cellular depolarisation. Synthetic agents that demonstrate K(+) channel opening properties are available for a variety of K(+) channel subtypes (e.g., K(ATP), BK(Ca), GIRK and M-channel). This study reviews the realistic therapeutic potential that may be gained in a broad spectrum of clinical conditions by K(+) channel openers. K(+) channel openers would therefore identify dysfunctional K(+) channel as therapeutic targets for clinical benefit, in addition being able to modulate normally functioning K(+) channels to gain clinical management of pathophysiological events irrespective of the cause.