乌拉坦对大鼠海马CA1区锥体神经元自发放电的抑制作用

为了深入研究麻醉药乌拉坦对大鼠海马CA1锥体神经元自发放电的作用及其机制,分析了10 mmol/L乌拉坦对自发放电、电压门控钠通道、电压门控钾通道的作用．从自发放电信号中计算了放电频率、提取了峰峰间隔序列(ISI)并利用样品熵和去趋势波动法对ISI进行了非线性分析．结果表明,乌拉坦不仅抑制了自发放电的频率,而且降低了自发放电ISI序列的复杂度并弱化了其长时程相关性．离子通道研究结果表明,乌拉坦显著地抑制了钠通道电流(I_Na),对延迟整流钾通道电流(I_K)和瞬时外向钾通道电流(I_A)虽然也有抑制作用但无统计学意义．由于乌拉坦不影响突触传递,因此它可能通过抑制I_Na使自发放电的阈值升高而降低放电频率,同时,由于参与的通道数量或活性降低而使得ISI的复杂度下降,长时程相关性弱化．     

白介素1β抑制培养的大鼠皮层神经元钠电流峰值和动作电位幅度

白介素1β(interleukin-1β,IL-1β)是重要的促炎细胞因子,在中枢神经系统的生理学和病理学过程中发挥关键作用.电压门控钠通道是可兴奋细胞电学活动的基础,控制神经元的兴奋性和动作电位.最近的研究又显示了IL-1β与电压门控通道之间的相互作用.为考察中枢神经元中IL-1β与电压门控钠通道之间的相互作用,本研...     

白介素1β抑制培养的大鼠皮层神经元钠电流峰值和动作电位幅度

白介素1β(interleukin-1β,IL-1β)是重要的促炎细胞因子,在中枢神经系统的生理学和病理学过程中发挥关键作用。电压门控钠通道是可兴奋细胞电学活动的基础,控制神经元的兴奋性和动作电位。最近的研究又显示了IL-1β与电压门控通道之间的相互作用。为考察中枢神经元中IL-1β与电压门控钠通道之间的相互作用,本研究使用10ng/mL的IL-1β处理培养的大鼠皮层神经元24h,通过电压钳技术测定电压门控钠电流,结果表明IL-1β处理抑制钠电流幅度,但不改变其激活和失活性质。与电压钳记录结果相一致,电流钳记录表明IL-1β降低动作电位幅度但不影响阈值。这些结果显示长时间的IL-1β处理可以抑制电压门控钠电流,这种抑制作用减小了动作电位幅度,这可能改变神经元的电学性质、突触传导等基本功能,并提示了IL-1β在神经系统损伤和疾病中作用的新的思路。     

心肌细胞晚钠通道的四种开放模式及其对动作电位的影响

应用膜片箝技术记录豚鼠游离心室肌细胞钠通道电流,发现晚钠通道电流可分为四种开放模式;单个短暂开放,散在开放,长时间长放和爆发型开放。它们的开放机率不一样,其中爆发型的机率为１／２０００,其开放时间常数比前三种大。离细胞体的小片膜电压箝制实验中,亦可观察到晚钠通道的这四种开放模式,它们均可被ＴＴＸ使波动现象基本消失,动作电位时程和有效不应期缩短,静息电位增加,表明晚钠通道的活动在动作电位平台期的形成     

电压门控钠通道结构与功能的适应性进化

电压门控钠通道是细胞兴奋性的重要分子基础,在进化演变中远早于神经元。伴随从细菌到脊椎动物的适应性演变,电压门控钠通道逐渐呈现出复杂的结构、功能和亚型多样性,且与诸多人类疾病密切相关。明确电压门控钠通道时空演变的适应性进化,解析电压门控钠通道的功能和结构多样性与人类重大疾病发生机制的相关性,有助于推进电压门控钠通道靶向临床诊疗新策略和新药的发现。     

海葵毒素对心肌钠通道开放模式、动作电位及心电图QT间期的影响

应用膜片箝技术记录游离豚鼠心肌细胞钠通道电流, 细胞内微电极技术记录心室乳头肌的动作电位和心电图机记录豚鼠的心电图。使用与心肌细胞钠通道有高度亲和力的海葵毒素(sea anemone toxin, ATXⅡ)改变钠通道开放的动力过程, 从三个水平来研究钠通道、动作电位、心电图变化的关系, 并试图探讨长QT综合征(long QT syndrome, LQTs)的发病机制。结果显示: ATXⅡ使钠通道的开放频率增加, 钠通道中“长时间开放模式”的开放时间常数增大, 动作电位的持续时间APD50和APD90也分别增加了23%和27%。 ATXⅡ使动物心电图QT间期延长18.6%, QTc (校正的QT间期)增大18.9%。这些结果提示, 钠通道动力过程的变化对动作电位和心电图QT间期有重要影响, 钠通道功能或结构的变异可能是临床上部分长QT综合征产生的原因。     

海葵毒素对心肌钠通道开放模式，动作电位及心电图QT周期的影响

应用膜片箝技术记录游离豚鼠心肌细胞的钠通道电流,细胞内微电极技术记录心室乳头肌的动作电位和心电图机记录豚鼠的心电图,使用与心肌;细胞钠通道有高度亲和力的海葵毒素（sea anemone toxin,ATXⅡ）改变钠通道开放的动力过程,从三个水平来研究钠通道,动作电位,心电图变化的关系,并试图探讨长QT综合征（long QT syndrome,LQTs)的发病机制,结果显示,ATXⅡ使钠通道的开放频率增加,钠通道中“长时间开放模式”的开放时间常数增大,动人电位的持续时间APD50和APD50也分别增加了23％和27％,ATXⅡ使动物心电图QT间期延长18．6％,QTc(校正的QT间期）增大18．9％,这些结果提示,钠通道动力过程的变化对动作电位和心电图QT间期有重要影响,钠通道功能或结构的变异可能是临床上部分长QT综合征产生的原因。     

电压门控钠离子通道疾病的研究进展

细胞膜上的电压门控钠离子通道（Voltage-gated Sodium Channels,VGSCs）是细胞形成动作电位过程中重要的组成构件,由一个大的α亚基和一个或多个不同的β亚基组成,中央是具高度选择性只允许钠离子通过的亲水通道。电压门控钠离子通道在调节细胞膜电位、维持细胞离子稳态、细胞增殖和凋亡等生理过程中发挥着重要作用,因而钠离子通道自身的异变或是相关基因的变异都可能引起一系列身体病变。本文主要介绍了电压门控钠离子通道的结构与功能,阐述了其与癌细胞侵袭转移和神经病理性疼痛的关系,并介绍了几种典型的由钠离子通道基因变异引起的疾病。随着对电压门控钠离子通道及其异常分子机制研究的不断深入,新成果将为生理学、药理学和病理学等领域的研究提供理论基础和新的研究思路,为离子通道疾病的临床预防、诊断与治疗找到新途径。     

味觉感受细胞离子通道和动作电位的建模与仿真

结合膜片钳测量的味觉感受细胞离子通道实验数据,提出了一个哺乳动物味觉感受细胞动作电位的数学模型.首先,建立了味觉感受细胞的电压门控Na＋通道和外向延迟整流K＋通道的模型,在此基础上建立了味觉感受细胞的单细胞计算模型.其次,仿真研究了味觉感受细胞在电刺激和酸味刺激下产生的动作电位,以及离子通道动力学特性对其的影响.该模型对于研究味觉感受细胞在味觉物质刺激下产生的动作电位及其离子通道的工作机制,以及味觉信息在外周神经的传递和信息编码具有指导意义。     

白介素1β对大鼠皮层神经元钠电流的急性作用

白介素1β(Interleukin-1β,IL-1β)是重要的促炎细胞因子,在多种中枢神经系统的损伤和疾病过程中发挥关键作用。电压门控的钠通道是神经元中最重要的离子通道之一,是产生再生性动作电位的基础,决定了神经元的兴奋性等电学性质,也与多种中枢疾病过程相关。然而,现在还没有直接关于IL-1β与中枢钠通道的相互关系的研究。在该研究中,使用全细胞膜片钳记录测定了IL-1β对培养的皮层神经元钠电流的急性作用,并分析了由此对动作电位的影响。结果显示,IL-1β对钠电流幅度只有较小的抑制,而显著降低钠通道的半激活电压,不改变激活的斜率因子和失活性质,这个作用引起动作电位阈值显著降低。这些结果提示在损伤和疾病过程中,快速释放的IL-1β可能会增加神经元兴奋性,从而恶化神经损伤过程。     

Light scattering and excitation in lobster giant axon Effects of ion substitution

Changes in the light scattering signal from single giant axons of lobster were observed during the propagation of the action potential in order to correlate membrane excitability with possible structural changes reflected in the optical properties of the axolemma. Substitution of guanidine and aminoguanidine for sodium resulted in a decreased action potential amplitude to 69 and 50% of control values, respectively. The amplitude of the light signal was, however, not significantly changed by these substitutions and is, therefore, reported to be independent of the transmembrane potential and current. The venom of the scorpion Leiurus quinquestriatus caused a marked prolongation of the action potential and the light scattering signal without significantly altering their amplitudes. A two-state model of the early (sodium) activation channel is suggested, in which the light scattering signal is correlated with a possible difference in the scattering efficiency between the states of the channel.     

Urethane inhibits the GABAergic neurotransmission in the nucleus of the solitary tract of rat brain stem slices

Because urethane is a widely used anesthetic in animal experimentation, in the present study, we evaluated its effects on neurons of the nucleus of the solitary tract (NTS) in brain stem slices from young rats (25-30 days old). Using the whole cell configuration of the patch-clamp technique, spontaneous postsynaptic currents (sPSCs) and evoked excitatory postsynaptic currents (eEPSCs) were recorded. Urethane (20 mM) decreased by approximately 60% the frequency of GABAergic sPSCs (1.0 +/- 0.2 vs. 0.4 +/- 0.1 Hz) but did not change the frequency, amplitude, or half-width of glutamatergic events or TTX-resistant inhibitory sPSCs [miniature inhibitory postsynaptic currents (IPSCs)]. Miniature IPSCs were measured in the presence of urethane plus 1 mM diazepam (1 mM), and no changes were seen in their amplitude. This suggests that the GABA concentration in the NTS synapses is set at saturating level. We also evaluated the effect of urethane on eEPSCs, and no significant change was observed in the amplitude of N-methyl-d-aspartate [NMDA; 44.2 +/- 11.5 vs. 37.6 +/- 10.6 pA (holding potential = 40 mV)] and non-NMDA currents [204.4 +/- 35.5 vs. 196.6 +/- 31.2 pA (holding potential = -70 mV)]. Current-clamp experiments showed that urethane did not alter the action potential characteristics and passive membrane properties. These data suggest that urethane has an inhibitory effect on GABAergic neurons in the NTS but does not change the spontaneous or evoked excitatory responses.     

Effects of furosemide on neural mechanisms in aplysia

The effects of furosemide on action potentials and responses to several neurotransmitters have been studied in the neurons of Aplysia. Furosemide (10^?7 and 10^?3M) does not visibly affect the normal action potential in R15 neurons. However, when TTX (30μM) is used to block the sodium component in R15, the remaining spike (presumably the calcium component) is increased in amplitude in the presence of furosemide. Furosemide also alters transmitter-induced conductances. Furosemide greatly reduces the amplitude and shifts, in a depolarizing direction, the reversal potential of chloride-dependent responses to γ-aminobutyric acid (GABA) and acetylcholine (ACh). This suggests that furosemide both blocks the chloride channel and inhibits a chloride pump. ACh-induced sodium responses were also reduced by furosemide but to a lesser extent than chloride responses. The potassium response to ACh and a voltage-dependent calcium response to serotonin were not altered. These results indicate that furosemide could alter synaptic responses both presynaptically by enhancement of calcium flux during the action potential and postsynaptically by blockade of chloride and sodium conductances.     

脊神经损伤后钠电流的变化及其离子通道机制

目的：检测脊神经切断大鼠背根节（DRG）神经元重复放电能力和钠电流的变化,并研究介导其电流变化的钠通道亚型的表达情况。方法：脊神经切断术后2～8d慢性痛大鼠模型背根节急性分离,对中等直径DRG神经元运用全细胞膜片钳技术记录神经元放电和钠电流的变化。对背根节神经元进行RT-PCR检测,分析其钠通道亚型的表达情况。结果：电流钳下,实验组DRG神经元在电流刺激下产生重复放电,而对照组神经元多诱发单个动作电位,电压钳记录发现实验组背根节神经元快钠电流和持续性钠电流幅值均明显大于对照组,PCR结果显示,Nav1.3、Nav1.7和Nav1.8通道亚型mRNA表达显著增高。结论：钠通道介导了脊神经受损模型的DRG神经元兴奋性增高,持续性钠电流可能通过调节阈下膜电位振荡的产生调节神经元兴奋性。     

TRPV4 links inflammatory signaling and neuroglial swelling

The activity of voltage-gated sodium channels contributes to onset and duration of the cardiac action potential through an intricate balance with the activity of other ion channels. Activation of sodium channels leads to membrane depolarization and Phase 0 of the cardiac action potential. Sodium channel fast inactivation contributes to Phase 1, the initial repolarization. Slow inactivation and closed state fast inactivation determine channel availability and, thus, overall membrane excitability. Defects in any of these biophysical states or transitions between them, imparted by (over 170 reported thus far, including both Long QT3 and Brugada syndromes) mutations in the (over 2000) amino acids that compose the sodium channel protein, can lead to channel dysfunction that manifests as an abnormal cardiac action potential and electrocardiogram. A causal relationship between several such abnormalities and the panoply of sodium channel mutations have led to a greater understanding of the molecular underpinnings of cardiac arrhythmias as well as a deeper appreciation for the intricacies of sodium channel function. Here, we review the literature regarding these causal relationships from a perspective of the biophysical properties of sodium channels.     

Biophysical defects in voltage.gated sodium channels associated with long QT and Brugada syndromes

The activity of voltage-gated sodium channels contributes to onset and duration of the cardiac action potential through an intricate balance with the activity of other ion channels. Activation of sodium channels leads to membrane depolarization and Phase 0 of the cardiac action potential. Sodium channel fast inactivation contributes to Phase 1, the initial repolarization. Slow inactivation and closed state fast inactivation determine channel availability and, thus, overall membrane excitability. Defects in any of these biophysical states or transitions between them, imparted by (over 170 reported thus far, including both Long QT3 and Brugada syndromes) mutations in the (over 2000) amino acids that compose the sodium channel protein, can lead to channel dysfunction that manifests as an abnormal cardiac action potential and electrocardiogram. A causal relationship between several such abnormalities and the panoply of sodium channel mutations have led to a greater understanding of the molecular underpinnings of cardiac arrhythmias as well as a deeper appreciation for the intricacies of sodium channel function. Here, we review the literature regarding these causal relationships from a perspective of the biophysical properties of sodium channels.     

The ionic requirements for the production of action potential in Achatina fulica Ferussac neuron

The ionic requirement for the production of directly elicited action potentials of a tonically auto-active neuron (TAN) in the subesophageal ganglia of the giant African snail, Achatina fulica Ferussac, was studied electrophysiologically. Calcium free Ringer solution containing 1 mM EDTA reversibly abolished the directly elicited action potential. Verapamil (10 micrograms/ml) or cocaine (4 mg/ml) decreased both amplitude and Vmax of the action potentials. The amplitude of the action potential was also slightly decreased in sodium free choline Ringer. However, tetrodotoxin did not significantly affect either the amplitude or Vmax of the directly elicited action potentials. The results suggest that the ionic requirement for generating action potential in snail neuron is not an ordinary sodium spike. Both calcium and sodium ions may participate in carrying charges across the membrane of the action potential.     

Mechanisms of use-dependent block of sodium channels in excitable membranes by local anesthetics

Many local anesthetics promote reduction in sodium current during repetitive stimulation of excitable membranes. Use-, frequency-, and voltage-dependent responses describe patterns of peak INa when pulse width, pulse frequency, and pulse amplitude are varied. Such responses can be viewed as reflecting voltage-sensitive shifts in equilibrium between conducting, unblocked channels and nonconducting, blocked channels. The modulated-receptor hypothesis postulates shifts in equilibrium as the result of a variable-affinity receptor and modified inactivation gate kinetics in drug-complexed channels. An alternative view considers drug blocking in the absence of these two features. We propose that drug binds to a constant-affinity channel receptor where receptor access is regulated by the channel gates. Specifically, we view channel binding sites as guarded by the channel gate conformation, so that unlike receptors where ligands have continuous access, blocking agent access is variable during the course of an action potential. During the course of an action potential, the m and h gates change conformation in response to transmembrane potential. Conducting channels with both gates open leave the binding site unguarded and thus accessible to drug, whereas nonconducting channels, with gates in the closed conformation, act to restrict drug access to unbound receptors and possibly to trap drug in drug-complexed channels. We develop analytical expressions characterizing guarded receptors as "apparently" variable-affinity binding sites and predicting shifts in "apparent" channel inactivation in the hyperpolarizing direction. These results were confirmed with computer simulations. Furthermore, these results are in quantitative agreement with recent investigations of lidocaine binding in cardiac sodium channels.     

丹参酮Ⅱ—A磺酸钠对分离的豚鼠心室肌单细胞慢反应...

The sodium channels of dissociated single ventricular cells of adult guinea pig heart were inactivated by partial depolarization in high K+ (25 mmol/L) Tyrode's solution and slow response action potential was elicited by intracellular stimulation. An obvious inhibition of the response was observed in the presence of 20 mumol/L sodium tanshinone II-A sulfonate (DS-201). In the concentration range from 1 mumol/L to 20 mumol/L, the inhibition effect of sodium tanshinone II-A sulfonate on the slow response action potentials enhanced by 0.28 mumol/L isoprenaline is concentration-dependent. Moreover, the inhibition effects of sodium tanshinone II-A sulfonate become stronger with the increase (in the range of 6.9 nmol/L to 0.55 mumol/L) of isoprenaline. The above-mentioned results suggest that sodium tanshinone II-A sulfonate may be a kind of effective calcium channel blocker. Under the effect of high concentration (50-100 mumol/L) of sodium tanshinone II-A sulfonate, the amplitude of fast response action potential of dissociated ventricular myocytes of adult guinea pig was decreased and the time to reach the peak was prolonged. All these results indicate that sodium channels were blocked to a certain extent by the high concentration of sodium tanshinone II-A sulfonate.     

Peripheral nerve at extreme low temperatures 2: Pharmacologic modulation of temperature effects

Changes in temperature have profound and clinically important effects on the peripheral nerve. In a previous paper, the effects of temperature on many properties of the peripheral nerve action potential (NAP) were explored including the NAP amplitude, conduction velocity and response to paired pulse stimulation. In this paper, the effects of pharmacologic manipulations on these parameters were explored in order to further understand the mechanisms of these effects.The reduction in conduction velocity with temperature was shown to be independent of the ionic composition of the perfusate and was unaffected by potassium or sodium channel blockade. This implies that the phenomenon of reduced conduction velocities at low temperature may be related to changes in the passive properties of the axon with temperature. Blockade of sodium channels and chronic membrane depolarization produced by high perfusate potassium concentrations or high dose 4-aminopyridine impair the resistance of the nerve to hypothermia and enhance the injury to the nerve produced by cycles of cooling and rewarming. This suggests the possibility that changes in the sodium inactivation channel may be responsible for the changes in the NAP amplitude with temperature and that prolonged sodium inactivation may lead more permanent changes in excitability.