Diphasic postsynaptic potential: a chemical synapse capable of mediating conjoint excitation and inhibition

Two identified interneurons in each buccal ganglion of Aplysia can mediate conjoined excitation and inhibition to a single follower cell. A single presynaptic action potential in one of these interneurons produces a diphasic, depolarizing-hyperpolarizing synaptic potential apparently as a result of a single transmitter acting on two types of postsynaptic receptors in the follower cell. These receptors produce synaptic potentials with differing reversal potentials, ionic conductances, time courses, rates of decrement with repetition, pharmacological properties, and functional consequences. The excitatory receptor controls a sodium conductance, the inhibitory receptor controls a chloride conductance. Both components of the synaptic potentials can be produced by iontophoretic application of acetylcholine on the cell body of the follower cell, and each component is differentially sensitive to different cholinergic blocking agents.     

Chemotransduction in the carotid body: K+ current modulated by PO2 in type I chemoreceptor cells

The ionic currents of carotid body type I cells and their possible involvement in the detection of oxygen tension (Po2) in arterial blood are unknown. The electrical properties of these cells were studied with the whole-cell patch clamp technique, and the hypothesis that ionic conductances can be altered by changes in PO2 was tested. The results show that type I cells have voltage-dependent sodium, calcium, and potassium channels. Sodium and calcium currents were unaffected by a decrease in PO2 from 150 to 10 millimeters of mercury, whereas, with the same experimental protocol, potassium currents were reversibly reduced by 25 to 50 percent. The effect of hypoxia was independent of internal adenosine triphosphate and calcium. Thus, ionic conductances, and particularly the O2-sensitive potassium current, play a key role in the transduction mechanism of arterial chemoreceptors.     

Distal initiation and active propagation of action potentials in interneuron dendrites

Fast and reliable activation of inhibitory interneurons is critical for the stability of cortical neuronal networks. Active conductances in dendrites may facilitate interneuron activation, but direct experimental evidence was unavailable. Patch-clamp recordings from dendrites of hippocampal oriens-alveus interneurons revealed high densities of voltage-gated sodium and potassium ion channels. Simultaneous recordings from dendrites and somata suggested that action potential initiation occurs preferentially in the axon with long threshold stimuli, but can be shifted to somatodendritic sites when brief stimuli are applied. After initiation, action potentials propagate over the somatodendritic domain with constant amplitude, high velocity, and reliability, even during high-frequency trains.     

Calcium channels in planar lipid bilayers: insights into mechanisms of ion permeation and gating

Electrophysiological recordings were used to analyze single calcium channels in planar lipid bilayers after membranes from bovine cardiac sarcolemmal vesicles had been incorporated into the bilayer. In these cell-free conditions, channels in the bilayer showed unitary barium or calcium conductances, gating kinetics, and pharmacological responses that were similar to dihydropyridine-sensitive calcium channels in intact cells. The open channel current varied in a nonlinear manner with voltage under asymmetric (that is, physiological) ionic conditions. However, with identical solutions on both sides of the bilayer, the current-voltage relation was linear. In matched experiments, calcium channels from skeletal muscle T-tubules differed significantly from cardiac calcium channels in their conductance properties and gating kinetics.     

Prolonged activation of mitochondrial conductances during synaptic transmission

Although ion channels have been detected in mitochondria, scientists have not been able to record ion transport in mitochondria of intact cells. A variation of the patch clamp technique was used to record ion channel activity from intracellular organelles in the presynaptic terminal of the squid. Electron microscopy indicated that mitochondria are numerous in this terminal and are the only organelles compatible with the tips of the pipettes. Before synaptic stimulation, channel activity was infrequent and its conductance was small, although large conductances ( approximately 0.5 to 2.5 nanosiemens) could be detected occasionally. During a train of action potentials, the conductance of the mitochondrial membrane increased up to 60-fold. The conductance increased after a delay of several hundred milliseconds and continued to increase after stimulation had stopped. Recovery occurred over tens of seconds.     

盐碱胁迫下羊草的生理特性与适应机制

[目的]探讨羊草在盐碱胁迫下的生理生化特性和K+、Na+含量的变化。[方法]在室内模拟不同pH盐碱土上种植羊草,并测定其生理生化指标和离子含量。[结果]随着土壤pH的逐渐升高和胁迫时间的延长,羊草体内的脯氨酸、可溶性蛋白、丙二醛的含量及氧化氢酶活性均随之增加,而后又逐渐降低。随着土壤pH的升高,羊草叶片的Na+含量逐渐增加,而K+含量逐渐减少,K+/Na+比值减小,但始终高于1。[结论]各项生理指标和K+、Na+含量的变化对维持羊草细胞的离子平衡起到了积极的调节作用。     

Cholinergic sensitivity: normal variability as a function of stimulus background

The sensitivity of the normally innervated iris sphincter to its neuro-transmitter, acetylchloline, and to relatd agents varies inversely with the preexisting physiological stimulus background, that is, the environmental light intnsity. This normal variability suggests the existence of a negative feedback mechahnism whereby sensitivity of the effector cell is modutlated by a product of neuronal activity.     

盐度变化对鱼类影响的研究进展

概括了盐度变化对鱼类产生的生理影响,主要从渗透调节酶、抗氧化酶、消化酶活性变化,离子细胞大小和数量的变化,凋亡及免疫细胞的活性变化,激素的分泌水平及其在组织内的表达水平变化,以及蛋白质标志因子在mRNA表达水平上的变化等方面,对鱼类适应盐度变化的应答机制进行了综述。     

A mechanosensitive ion channel in the yeast plasma membrane

Mechanosensitive ion channels use mechanical energy to gate the dissipation of electrochemical gradients across cell membranes. This function is fundamental to physiological processes such as hearing and touch. In electrophysiological studies of ion channels in the plasma membrane of the yeast Saccharomyces cerevisiae, channels were observed that were activated by, and adapted to, stretching of the membrane. Adaptation of channel activity to mechanical stimuli was voltage-dependent. Because these mechanosensitive channels pass both cations and anions, they may play a role in turgor regulation in this walled organism.     

植物耐盐性生理生化指标的综合评价

综述了近年来耐盐性植物地上部分无机离子、脯氨酸、甜菜碱、多胺、酶活性、膜透性与丙二醛含量、叶绿素含量、植物激素、呼吸作用、光合作用等耐盐性生理生化指标研究进展,并在此基础上综合评价了其对选育培育植物耐盐新品种的重要性及指示意义.     

Hemicholinium-3: noncholinergic effects on squid axons

Hemicholinium-3, when applied to the inside of a squid axon, is effective in blocking the action potential. This action is not antagonized by the addition of choline or acetylcholine to the perfusate. Voltage-clamp experiments show that hemicholinium-3 depresses both the early transient and late steady-state components of membrane ionic conductances, with a greater effect on the peak transient component.     

咪唑型离子液体溶液中纤维素酶荧光活性测定

为考查纤维素酶在离子液体溶液中的酶活,采用荧光光谱分析法对离子液体中纤维素酶的荧光活性测定,研究离子液体的浓度、类型对纤维素酶的活性影响。结果表明:纤维素酶在咪唑类离子液体溶液中荧光活性随离子液体浓度的升高而降低。离子液体为[C4 mim]Cl、[C4 mim]Br,且浓度为0.1 mol/L使纤维素酶的荧光强度减低最小,即对酶活性影响最小。     

植物液泡膜H+-ATPase和H+-PPase研究进展

植物液泡膜 ATP 酶（H+-ATPase）和液泡膜焦磷酸酶（H+-PPase）是液泡膜上两个含量丰富的蛋白,其功能的正常发挥在植物生长发育过程中扮演着重要角色。液泡膜 H+-ATPase 和 H+-PPase 水解底物释放能量,同时产生大量 H+由胞质泵入液泡内,形成细胞质与液泡间的 H+ 电化学势梯度,为多种溶质分子的跨膜主动运输提供驱动力,维持细胞内的离子稳态和渗透平衡,为细胞内各种生理生化反应的正常运行提供保障。此外,液泡作为植物细胞离子养分的储存库,其膜上 H+-ATPase 和 H+-PPase 能够通过改变其活性来调控硝酸盐在胞质和液泡间的分配比例,进而影响植物的氮素利用效率。在逆境胁迫条件下,提高液泡膜 H+-ATPase 和 H+-PPase 的活性有利于提高植株对逆境的适应能力,从而减少逆境胁迫对植株生长发育造成的不利影响。介绍了植物液泡膜 H+-ATPase 和 H+-PPase 的结构特征及其在植物生长发育过程中的生理功能,并对其在植物抵御非生物逆境胁迫过程中发挥的重要作用进行阐述,为进一步提高作物的氮素利用率及逆境适应能力提供方向。     

Neuronal phosphoproteins: physiological and clinical implications

The presence of a great variety of neuron-specific phosphoproteins in nervous tissue supports the view that protein phosphorylation plays many roles in neuronal function. The physiological significance of several of these phosphoproteins has already been established. Some neuronal phosphoproteins have been detected throughout the entire nervous system, whereas the distribution of others is limited to one or a few neuronal cell types. These various neuron-specific phosphoproteins are proving of value in the study of the physiology, anatomy, developmental biology, and pathophysiology of the nervous system.     

Imaging elemental distribution and ion transport in cultured cells with ion microscopy

Both elemental distribution and ion transport in cultured cells have been imaged by ion microscopy. Morphological and chemical information was obtained with a spatial resolution of approximately 0.5 micron for sodium, potassium, calcium, and magnesium in freeze-fixed, cryofractured, and freeze-dried normal rat kidney cells and Chinese hamster ovary cells. Ion transport was successfully demonstrated by imaging Na+-K+ fluxes after the inhibition of Na+- and K+ -dependent adenosine triphosphatase with ouabain. This method allows measurements of elemental (isotopic) distribution to be related to cell morphology, thereby providing the means for studying ion distribution and ion transport under different physiological, pathological, and toxicological conditions in cell culture systems.     

Beta-N-methylamino-L-alanine neurotoxicity: requirement for bicarbonate as a cofactor

Ingestion of the excitotoxic cycad seed amino acid beta-N-methylamino-L-alanine may be responsible for the neuronal degeneration associated with Guam amyotrophic lateral sclerosis-parkinsonism-dementia in man. However, the basis for the central neurotoxicity of beta-N-methylamino-L-alanine has been unclear, as it lacks the omega acidic (or equivalent electronegative) moiety characteristic of other excitatory amino acids. beta-N-methylamino-L-alanine produced neurotoxic and neuroexcitatory effects in murine cortical cell cultures only when physiological concentrations of bicarbonate were available in the extracellular bathing medium. Bicarbonate may interact noncovalently with beta-N-methylamino-L-alanine to produce, in combination, a molecular configuration that activates glutamate receptors.     

The intrinsic electrophysiological properties of mammalian neurons: insights into central nervous system function

This article reviews the electroresponsive properties of single neurons in the mammalian central nervous system (CNS). In some of these cells the ionic conductances responsible for their excitability also endow them with autorhythmic electrical oscillatory properties. Chemical or electrical synaptic contacts between these neurons often result in network oscillations. In such networks, autorhythmic neurons may act as true oscillators (as pacemakers) or as resonators (responding preferentially to certain firing frequencies). Oscillations and resonance in the CNS are proposed to have diverse functional roles, such as (i) determining global functional states (for example, sleep-wakefulness or attention), (ii) timing in motor coordination, and (iii) specifying connectivity during development. Also, oscillation, especially in the thalamo-cortical circuits, may be related to certain neurological and psychiatric disorders. This review proposes that the autorhythmic electrical properties of central neurons and their connectivity form the basis for an intrinsic functional coordinate system that provides internal context to sensory input.     

不同杏梅、杏李品种枝条抗寒性研究

分别以金光杏梅、红杏梅、风味玫瑰、味王、味啼及恐龙蛋等6个杏梅、杏李品种为试材.对不同品种枝条的抗寒生理特性进行了研究.结果表明.金光杏梅、红杏梅及风味玫瑰的休眠枝自由水/束缚水含量的比值明显高于味王、味啼及恐龙蛋;随着处理温度的降低,各品种枝条的相对电导率逐渐增大,增大的程度由大到小顺序是风味玫瑰、红杏梅、金光杏梅、恐龙蛋、味王、味啼;并且各品种枝奈的脯氨酸及可溶性糖的含量也呈增加趋势,其中味啼、金光杏梅、恐龙蛋增加的幅度大于风味玫瑰、味王和红杏梅.研究结果初步表明,味啼、金光杏梅和恐龙蛋比风味玫瑰、味王和红杏梅具有较强的抗寒性.     

乙烯代谢途径中基因表达与器官脱落研究进展

器官脱落是一种由各种因素共同调节的复杂生理过程,多种激素对其都有影响,其中乙烯对脱落的影响最大.乙烯含量的上升和器官脱落正相关,但乙烯含量的上升和器官脱落之间并非相邻的两个步骤.器官脱落首先须使植物体本身乙烯合成量增加,之后通过乙烯受体基因和乙烯进行结合,再通过乙烯信号传递体把乙烯上升信号传递下去,从而引起离区细胞壁水解酶活性增强和基因表达量上升,进而导致离区细胞壁发生破碎,最终导致器官脱落.综述了乙烯代谢途径中的乙烯合成、膜上乙烯受体、乙烯膜内信号传递体与器官脱落的研究进展.     

神经素的研究进展

神经素是一个由33个氨基酸组成的神经肽,在不同物种中都有较高的保守性,在脑、内分泌组织、神经分泌组织和神经组织中特异表达。SN的前体蛋白是成熟的神经递质,被命名为Secretogranin Ⅱ(SgⅡ),属于嗜铬类蛋白家族。SN前体mRNA的表达水平很大程度上由细胞的去极化所调节,也可作为长期和瞬时神经活性变化的有用标记。在病理生理条件下,尤其是在细胞缺氧时,SN可以在非内分泌组织中表达。SN可特异、高效地吸引单核细胞,嗜曙红细胞形成浓度梯度,并且有促进血管生长的作用。因此,SN可介导神经性炎症反应,并且在由缺氧导致的局部缺血的症状中,SN可能与神经血管生成有关。