外加电场刺激对菲降解菌的影响

以菲为主要C源,吐温80作为增溶剂,研究细菌Enterobacter dissolvens在直流电和交流电条件下的生长和代谢过程。实验结果表明:当施加10 mA直流电时,通电8 h后,菌液中细胞的菲降解率较对照增长1.6倍,细胞生长亦有所加快;而施加交流电时,细菌生长和菲降解率均低于直流电刺激。     

大肠杆菌的直流电场刺激过程

以钛网电极和铂网电极对培养瓶中大肠杆菌生长过程进行加电刺激,研究其在直流电场作用下的生长情况,并结合循环伏安扫描、恒电流、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)及测定菌体ATP酶活力等技术对大肠杆菌的直流电场刺激过程进行研究。结果表明,在0-0.2275mA/cm2范围内,随着电流密度的增加,直流电场对大肠杆菌生长量的增长促进作用逐渐增加,而0.0455mA/cm2的电场则是获得最大活菌量的最适电流密度;通过对析氢活性不同的铂网电极与钛网电极通加相同电流密度的电场,发现铂电极培养体系菌体生长优于钛电极培养体系菌体的生长。经验证发现引起这种变化的原因主要是水的阴极电解产物吸附氢和氢气比例的不同引起的;同时发现在0.091mA/cm2电流密度下,直流电场能有效提高ATP酶的活力,在8h时通电菌样酶活为不通电菌样酶活的3.2倍;通过对0.0455mA/cm2直流电场刺激后的菌体蛋白进行SDS-PAGE分析发现加电菌体在分子量25kD与35kD左右多肽表达量明显高于不加电菌体的多肽表达量,而在分子量为66.2kD左右时多肽表达量低于不加电菌体多肽表达量。     

Cerbinal,a Pseudoazulene Iridoid,as a Potent Antifungal Compound Isolated from Gardenia jasminoides Ellis

d-Gluconate dehydrogenase isolated from Pseudomonas fluorescens was immobilized on the surfaces of carbon and gold electrodes by irreversible adsorption. The electrodes with the adsorbed enzyme produced anodic currents in solutions containing d-gluconate. The currents were attributable to the electro-enzymic oxidation (direct bioelectrocatalytic oxidation) of d-gluconate; the electrochemical system required no external redox molecules serving as mediators of electron transfer between the electrode and the adsorbed enzyme. A model of the direct bioelectrocatalysis at the enzyme-modified electrodes is presented.     

细菌Enterobacter dissolvens的电解刺激连续培养过程研究

以葡萄糖为唯一碳源,研究了细菌Enterobacter dissolvens在直流电条件下的连续培养过程。实验表明在电解刺激下的连续培养,细胞生长曲线和葡萄糖代谢速率均显著提高。当采用10mA电流通电10h后,菌液中细胞的比脱氢酶活[总显色度（OD490）／细胞量（OD600）]约为参比样的2倍,而葡萄糖降解率也为参比测量值的1．8倍,细胞生长亦有所加快。由于培养基的流加,使得过氧化氢等中间产物得到稀释,从而避免了细胞生长的衰减。     

Mediated amperometry reveals two distinct modes of yeast responses to glucose

Mediated amperometry was exploited to monitor intracellular redox activity without cell disruption. Continuous measurements of menadione-mediated glucose currents at carbon paste electrodes with various immobilized intact wild type yeasts (Saccharomyces cerevisiae, Candida pulcherrima, Clavispora lusitaniae, Wickerhamomyces anomalus, Pichia guilliermondii, Kluyveromyces lactis var. lactis, Debaryomyces hansenii, Candida zeymolaydes and Candida tropicalis) revealed two distinct and previously unreported modes of development of the currents during the first 2 to 3 min. after subjection to glucose. A correlation among the values of the currents and the capacities of wild type yeasts to secrete various substances was observed.     

Influence of long-term low direct current on rat ischiadic nerves

The effects of a low direct current on peripheral nerves and electrodes on the ischiadic nerve were investigated, and a constant direct current was applied for various time periods. Afterwards clinicophysiological tests and histological evaluations were performed. The muscles of 55 rats could be stimulated by external stimulation during the follow-up examinations, but 90% of all animals showed microscopically visible nerve tissue alterations which might have been caused by mechanical rather than electrolytic factors.     

Location and dynamic properties of the spike generator in an insect mechanosensory neuron

1.The cereal bristle hairs of the cockroach, Periplaneta americana, are each innervated by one mechanosensory cell and 1–5 chemosensory cells. In transepithelial recordings, chemo- and mechanosensory spikes could be discriminated from each other by their relative amplitude. 2. When current steps were applied via the sensory hair, trains of impulses were triggered whatever the polarity of the current. 3. All responses adapted to the current, but the time course of adaptation was fitted by a power law for outward currents and an exponential law for inward currents. 4. During application of outward currents, the spikes showed a negative initial phase on which a small positive component was superimposed; strong polarizations produced purely negative spikes. More classical spikes with a positive initial phase were induced by inward currents. 5. The present work supports the hypothesis of a direct excitability of the apical dendrite in cereal bristle mechanoreceptors and confirms previous results suggesting that spikes are normally triggered within that region during mechanical stimulations. It is also established, for the first time, that adaptation to currents may be different in the apical dendrite and in more basal regions of the same mechanosensory neuron.Abbreviation RP receptor potential - TEV transepithelial voltage - TTX tetrodotoxin     

Extracellular electrical fields direct wound healing and regeneration

Endogenous DC electric fields (EFs) are important, fundamental components of development, regeneration, and wound healing. The fields are the result of polarized ion transport and current flow through electrically conductive pathways. Nullification of endogenous EFs with pharmacological agents or applied EFs of opposite polarity disturbs the aforementioned processes, while enhancement increases the rate of wound closure and the extent of regeneration. EFs are applied to humans in the clinic, to provide an overwhelming signal for the enhancement of healing of chronic wounds. Although clinical trials, spanning a course of decades, have shown that applied EFs enhance healing of chronic wounds, the mechanisms by which cells sense and respond to these weak cues remains unknown. EFs are thought to influence many different processes in vivo. However, under more rigorously controlled conditions in vitro, applied EFs induce cellular polarity and direct migration and outgrowth. Here we review the generation of endogenous EFs, the results of their alteration, and the mechanisms by which cells may sense these weak fields. Understanding the mechanisms by which native and applied EFs direct development and repair will enable current and future therapeutic applications to be optimized.     

Correlation of electrical current influx with nuclear position and division inFunaria caulonema tip cells

Summary Ionic currents around caulonema tip cells of the filamentous protonema of the mossFunaria hygrometrica were examined using a nonintrusive vibrating microelectrode to map electrical current before and during mitosis. Tip cells in interphase generate inward electrical currents that are maximal at the nuclear region. These currents remain concentrated over the nucleus as it migrates forward maintaining a constant distance from the growing tip. Just prior to mitosis this inward current increases twofold. During mitosis and cytokinesis current at the nuclear zone increases to four times the resting level and fluctuates, falling to zero after cell plate fusion with parental walls. The locus of outward current could not be dectected. These results suggest that plasma membrane ion currents may regulate both nuclear positioning and subsequent temporal and spatial control of cell division.     

In situ rheology of yeast biofilms

The aim of the present work was to investigate the in situ rheological behavior of yeast biofilms growing on stainless steel under static and turbulent flow. The species used (Rhodototula mucilaginosa, Candida krusei, Candida kefyr and Candida tropicalis) were isolated from a clarified apple juice industry. The flow conditions impacted biofilm composition over time, with a predominance of C. krusei under static and turbulent flow. Likewise, structural variations occurred, with a tighter appearance under dynamic flow. Under turbulent flow there was an increase of 112 μm in biofilm thickness at 11 weeks (p < 0.001) and cell morphology was governed by hyphal structures and rounded cells. Using the in situ growth method introduced here, yeast biofilms were determined to be viscoelastic materials with a predominantly solid-like behavior, and neither this nor the G’₀ values were significantly affected by the flow conditions or the growth time, and at large deformations their weak structure collapsed beyond a critical strain of about 1.5–5%. The present work could represent a starting point for developing in situ measurements of yeast rheology and contribute to a thin body of knowledge about fungal biofilm formation.     

Airway epithelial wounds in rhesus monkey generate ionic currents that guide cell migration to promote healing

Damage to the respiratory epithelium is one of the most critical steps to many life-threatening diseases, such as acute respiratory distress syndrome and chronic obstructive pulmonary disease. The mechanisms underlying repair of the damaged epithelium have not yet been fully elucidated. Here we provide experimental evidence suggesting a novel mechanism for wound repair: endogenous electric currents. It is known that the airway epithelium maintains a voltage difference referred to as the transepithelial potential. Using a noninvasive vibrating probe, we demonstrate that wounds in the epithelium of trachea from rhesus monkeys generate significant outward electric currents. A small slit wound produced an outward current (1.59 μA/cm(2)), which could be enhanced (nearly doubled) by the ion transport stimulator aminophylline. In addition, inhibiting cystic fibrosis transmembrane conductance regulator (CFTR) with CFTR(Inh)-172 significantly reduced wound currents (0.17 μA/cm(2)), implicating an important role of ion transporters in wound induced electric potentials. Time-lapse video microscopy showed that applied electric fields (EFs) induced robust directional migration of primary tracheobronchial epithelial cells from rhesus monkeys, towards the cathode, with a threshold of <23 mV/mm. Reversal of the field polarity induced cell migration towards the new cathode. We further demonstrate that application of an EF promoted wound healing in a monolayer wound healing assay. Our results suggest that endogenous electric currents at sites of tracheal epithelial injury may direct cell migration, which could benefit restitution of damaged airway mucosa. Manipulation of ion transport may lead to novel therapeutic approaches to repair damaged respiratory epithelium.     

Mediatorless electrocatalytic reduction of hydrogen peroxide at graphite electrodes chemically modified with peroxidases

The electrocatalytic reduction of H₂O₂ was studied for carbonaceous electrodes modified with horse-radish peroxidase (HRP), microperoxidase (MP), and lactoperoxidase (LP). The carbonaceous electrodes were of three different graphites, carbon and glassy carbon. The peroxidase modified electrode was inserted as the working electrode in a flow through amperometric cell of the wall jet type and connected to a flow injection system. The effect of different pretreatments of the electrode surface prior to adsorption of the enzyme was investigated. Heating the electrodes in a muffle furnace at 700°C for 1.5 min was found to yield the highest currents. The electrocatalytic current for HRP-modified electrodes starts at about +600 mV vs. Ag/AgCl (pH 7.0) and reaches a maximum value at about −200 mV. For MP- and LP-modified electrodes the currents start at a lower potential (≈ 300 mV). For the best electrode material for HRP, straight calibration curves were obtained between 1 and 500 μM H₂O₂ at 0 mV. The mechanism for the electron transfer from the electrode to the adsorbed peroxidase is discussed. Deliberate modification of the electrode surface with quinoid type electroactive species was found to mediate the reaction. It is proposed that spontaneously occurring electrochemically active surface groups mediate the electron transfer to the adsorbed enzyme. However, a contribution to the observed current from a direct electron transfer cannot be ruled out.     

Calcium-dependent sodium current in the marine ciliateEuplotes vannus

Summary Ca and Na inward currents were recorded upon depolarizations inEuplotes after the blockage of K outward currents with intracellular Cs ions. The Na current was analyzed under voltage clamp and had the following properties: it activated to a maximum within 150 msec and partly inactivated during sustained voltage steps. It had a positive equilibrium potential between 25 and 30 mV and could be carried by Na or Li ions but not by K, choline or Tris ions. The current revealed a prominent associated inward tail current which deactivated with a single-exponential time constant of 118 msec. Both the current and its tail were strongly reduced after reduction of the extracellular Na concentration. Externally applied K channel blocker tetraethylammonium chloride did not block the current. Either EGTA injection into the cell or nonlethal deciliation with ethanol eliminated the current and its tail. These results indicate the existence of a Na conductance within the membrane ofEuplotes which is activated by the intracellular level of free Ca²⁺.     

Simultaneous measurement of changes in current and tracer flux in voltage-clamped squid giant axon.

A method is described for the simultaneous measurement of changes in membrane current and unidirectional radiotracer flux in internally dialyzed voltage-clamped squid giant axons. The small currents that are produced by electrogenic transport processes or steady-state ionic currents can be resolved using this method. Because the use of grounded guard electrodes in the end pools is not, by itself, an adequate means of eliminating end-effects, two ancillary end pool clamp circuits are described to eliminate extraneous current flow from the ends of the axon. The end pool voltage-clamp circuits serve to minimize net current flow between the end pools and center pool, and employ stable, low-impedance calomel electrodes to monitor the potentials of the end and center pools. The adequacy of the method is demonstrated by experiments in which unidirectional 22Na efflux and current, flowing through tetrodotoxin (TTX)-sensitive Na channels into Na-free seawater, under K-free conditions, are shown to be equal. The equality of unidirectional TTX-sensitive flux and current is maintained over the entire range of membrane potentials examined (-60 to +20 mV). The method has been applied to a series of experiments in which the voltage dependence and stoichiometry of the Na/K pump have been measured (Rakowski et al., 1989), and can be applied in general to the simultaneous measurement of changes in current and flux of other electrogenic transport processes, and of currents through ionic channels that open under steady-state conditions.     

Effect of electrical fields and external ionic currents on pollen-tube orientation

Summary Agapanthus umbelatus pollen tubes (PTs) display a number of different growth patterns when germinated in an electric field of 750 mV· mm^–1. When pollen is germinated near the cathode (82.44% of orientation to the cathode side) or near the anode (55.35% of orientation to the anode), growth is oriented parallel to the applied field but when germinated at an intermediate position, there is random growth. An increase and decrease in the orientation rates as well as reversion of the polarized growth were observed when the growth conditions were systematically altered. These findings reflect the influence of different ionic currents present in the germination medium. These ionic currents induce the formation of ionic gradients, which were monitored by ion-HPLC. The individual omission of Ca²⁺, K⁺, Mg²⁺ and Cl^– suppresses or alters the oriented growth pattern. The presence of ionic gradients is not by itself suficient to trigger the polarization of tube growth as the presence of an electric field which drives the ionic currents is essential for this to occur.Abbreviations PT Pollen tube - DNS 3,5-dinitro salycilic acid; - TP transient polarization - HPLC high precision liquid chroma tography - DC direct current     

Effects of direct electric current on Herpetomonas samuelpessoai: An ultrastructural study

The literature shows that the effects of direct electric currents on biological material are numerous, including bactericidal, fungicidal, parasiticidal, and anti‐tumoral, among others. Non‐pathogenic trypanosomatids, such as Herpetomonas samuelpessoai, have emerged as important models for the study of basic biological processes performed by a eukaryotic cell. The present study reports a dose‐dependent anti‐protozoan effect of direct electric treatment with both cathodic and anodic current flows on H. samuelpessoai cells. The damaging effects can be attributable to the electrolysis products generated during electric stimulation. The pH of the cell suspension was progressively augmented from 7.4 to 10.5 after the cathodic treatment. In contrast, the anodic treatment caused a pH decrease varying from 7.4 to 6.5. Transmission electron microscopy analyses revealed profound alterations in vital cellular structures (e.g., mitochondrion, kinetoplast, flagellum, flagellar pocket, nucleus, and plasma membrane) after exposure to both cathodic and anodic current flows. Specifically, cathodic current flow treatment induced the appearance of autophagic‐like structures on parasite cells, while those submitted to an anodic current flow presented marked disorganization of plasma membrane and necrotic appearance. However, parasites treated in the intermediary chamber (without contact with the electrodes) did not present significant changes in viability or morphology, and no pH variation was detected in this system. The use of H. samuelpessoai as a biological model and the direct electric current experimental approach used in our study provide important information for understanding the mechanisms involved in the cytotoxic effects of this physical agent. Bioelectromagnetics 33:334–345, 2012. © 2011 Wiley Periodicals, Inc.     

Transient currents carried by the uncoupler,carbonyl cyanide m-chlorophenylhydrazone

The weak acid uncoupler, carbonyl cyanide m-chlorophenylhydrazone, carries protons across lipid membranes. As predicted by the carrier model, at low pH, the current changes immediately following a jump in applied potential and then remains constant. By contrast at high pH, the currents relax from an initial value to a lower value as the carrier anions redistribute in the membrane. These relaxations are slower than those seen with other lipid-soluble anions which presumably explains why they had not been detected previously.     

The metabolism of long-chain fatty acids and alcohols byCandida tropicalis andSaccharomyces cerevisiae

The factors affecting the growth ofCandida tropicalis andSaccharomyces cerevisiae on medium- and long-chain fatty acids and alcohols in batch culture were investigated. Growth on solid acids and alcohols dispersed in the medium is a maximum for tetradecanoic acid and tetradecanol. The poorer growth observed on shorter chain lengths can be ascribed to their toxicity to the yeasts, whilst the fall off in growth on the higher members is explained by their increasing insolubility in the medium. When the longer-chain-length acids are dissolved in a non-metabolisable hydrocarbon, the growth ofC. tropicalis is improved, but that ofS. cerevisiae is unaffected. This suggests that acids can enter the cells of the former organism by direct contact with the hydrocarbon droplets. The surface ofS. cerevisiae is too hydrophilic for this transfer mechanism to be possible. Fatty acids dissolved in gas oil are utilized as substrates for the growth ofCandida tropicalis in competition with then-paraffins contained in the gas oil. Each fatty acid contributes to a constant proportion of yeast produced, but this proportion decreases as the chain is lengthened. Thus, in mixtures of gas oil with dodecanoic acid, 65% of the yeast is produced from metabolism of the acid, while with octadecanoic acid only 15% is produced. The log specific rates of utilization of the fatty acids within this range diminish linearly with increasing chain length.     

Wound-Induced Changes of Membrane Voltage,Endogenous Currents,and Ion Fluxes in Primary Roots of Maize

The effects of mechanical wounding on membrane voltage, endogenous ion currents, and ion fluxes were investigated in primary roots of maize (Zea mays) using intracellular microelectrodes, a vibrating probe, and ion-selective electrodes. After a wedge-shaped wound was cut into the proximal elongation zone of the roots, a large inward current of approximately 60 [mu]A cm-2 was measured, together with a change in the current pattern along the root. The changes of the endogenous ion current were accompanied by depolarization of the membrane voltage of cortex cells up to 5 mm from the wound. Neither inhibitors of ion channels nor low temperature affected the large, wound-induced inward current. The fluxes of H+, K+, Ca2+, and Cl- contributed only about 7 [mu]A cm-2 to the wound-induced ion current. This suggests the occurrence of a large mass flow of negatively charged molecules, such as proteins, sulfated polysaccharides, and galacturonic acids, from the wound. Natural wounding of the root cortex by developing lateral roots caused an outwardly directed current, which was clearly different in magnitude and direction from the current induced by mechanical injury.     

Electrochemical measurements with glucose oxidase immobilized in polyacrylamide gel: Constant current voltametry

Constant current voltametry was shown to be a suitable method for evaluation of electrodes containing immobilized oxidative enzymes as catalysts. The half-cell potential for the oxdidation of D -glucose at constant pH was measured at a series of constant dc currents, using glucose oxidase immobilized in a polyacrylamide gel-platinum gauze matrix as catalyst. Over the range studied the potential versus current data were linear and could be extrapolated to give the open-circuit half-cell potential at zero current. The difference between the measured potential and the open-circuit potential at a constant current was indicative of the loss in useful voltage due to concentration gradients within or adjacent to the enzyme electrode assembly. The relationship between the open-circuit potential and the pH of the reaction mixture was linear with a slope of ?0.056, in good agreement with the predicted slope of ?0.061.