Maximum Membrane Potential Research Articles

Analysis of seed quality indicators based on neural network

The paper presents a neural network study of the data of wheat seed quality. It is established that the analysis of bioelectrical signals of wheat seeds based on a neural network can be used in practice for the solution of two problems - diagnostics of seed material quality and the evaluation of cleaning line quality (separation into fractions). The paper presents the results of initial data preparation, formation of a neural network, analysis of training data for two practical problems of classification. It was established using a neural network that there is a nonlinear dependence of the membrane potential maximum value and the signal rise time on the seed yield. The model makes it possible to predict yield in terms of the seed material quality. A nonlinear dependence of the maximum membrane potential, the signal rise time of wheat seeds and the seeds variety to one or another faction (speed of separation into the fractions in this example) was also established in this paper. Studies have shown that the seeds variety is an important informative feature for solving the problem of classifying seeds by fractions. Therefore, it is necessary to conduct additional studies with other wheat seeds varieties to apply this method in practice.

Determination of Adequate Defibrillation of Ventricular Tachycardia Using Computer Simulation of Electroporation Aftershock Effects on Human Cardiomyocytes

Electric defibrillation is a life-saving therapy for clinically dangerous ventricular arrhythmias. Unfortunately, direct-current (DC) shock treatment often induces or worsens other tachyarrhythmias. The adverse effects of electric shock delivered to human ventricular cardiomyocytes are not fully understood. This study thus uses computer simulation to investigate the pathogenesis of the electrophoresis in epicardial and endocardial human tissue. The O'Hara-Rudy dynamic human ventricular cell model incorporated with Ohuchi's mathematical DC shock model is used. The effect of electroporation is described as a transmembrane pore, mimicking the reversible breakdown of the cell membrane. The aftershock effects on epiardial and endocardial ventricular cardiomyocytes are evaluated. The effects of delivering shock from the endocardium and epicardium using a multicellular one-dimensional strand model are also investigated. Ventricular tachycardia can be terminated by a low-strength shock to endocardial cardiomyocytes. However, an excessively strong shock to epicardial cardiomyocytes induces early afterdepolarization and is arrhythmogenic. The aftershock effect of the electroporation is serious for epicardial ventricular myocytes. The optimization of defibrillation energy delivery to the maximum membrane potential and the pathogenesis of the aftershock effect during ventricular tachycardia are also investigated. The aftershock effect of electroporation is more serious in epicardial cells than it is in endocardial cells. It is suggested that the DC shock be delivered to endocardium cells before the maximum membrane potential of the epicardial cell in a multicellular one-dimensional strand model is reached, which is before the electrocardiogram R wave spike.

Resonant response of a Hodgkin-Huxley neuron to a spike train input

Introduction Experiments show that neurons have a tendency to respond to signals tuned to a resonant frequency [1]. In order to understand the general properties of a resonant response of a neuron, we study the silent Hodgkin-Huxley neuron driven by periodic input. The current arriving through the synapse consists of a set of spikes Ip(t) ~ gsyn (t/) exp(-t/) C(t) (Va-Vsyn), where gsyn is the synapse conductivity,  is the time constant associated with the synapse conduction, Va is the maximum membrane potential and Vsyn is the reversal potential of the synapse.

Electrical behavior and pore accumulation in a multicellular model for conventional and supra-electroporation

Extremely large but very short (20kV/cm, 300ns) electric field pulses were reported recently to non-thermally destroy melanoma tumors. The stated mechanism for field penetration into cells is pulse characteristic times faster than charge redistribution (displacement currents). Here we use a multicellular model with irregularly shaped, closely spaced cells to show that instead overwhelming pore creation (supra-electroporation) is dominant, with field penetration due to pores (ionic conduction currents) during most of the pulse. Moreover, the model’s maximum membrane potential (about 1.2V) is consistent with recent experimental observations on isolated cells. We also use the model to show that conventional electroporation resulting from 100 microsecond, 1kV/cm pulses yields a spatially heterogeneous electroporation distribution. In contrast, the melanoma-destroying pulses cause nearly homogeneous electroporation of cells and their nuclear membranes. Electropores can persist for times much longer than the pulses, and are likely to be an important mechanism contributing to cell death.

Membrane potential based characterization by flow cytometry of physiological states in an aerobic anoxygenic phototrophic bacterium

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 37:149-158 (2004) - doi:10.3354/ame037149 Membrane potential based characterization by flow cytometry of physiological states in an aerobic anoxygenic phototrophic bacterium Nianzhi Jiao*, Yinjie Yang, Tingwei Luo Ministry of Education Key Lab for Marine Environmental Sciences, Center for Environmental Sciences, Xiamen University,Xiamen 361005, PR China *Email: jiao@xmu.edu.cn ABSTRACT: A simplified protocol for determination of bacterial membrane potential (MP) by flow cytometry with 3,3’-dihexyloxacarbocyanine iodide (DiOC6(3)) as the MP probe was established, and was applied to an aerobic anoxygenic phototrophic bacterium (AAPB strain, Roseobacter clade) with an Escherichia coli strain as a reference. It was shown to be capable of precise indication of the physiological states of the cells as well as cellular responses to environmental factors. Based on the experimental results, a MP curve model was proposed for characterization of species-specific features, which offers parameters including the maximum MP of the curve (MPmax), the time to reach the MPmax (Tmax), the slope of the exponential phase of the MP curve (KMP), and the minimum (threshold) concentration of a particular substrate required for the organism to reach its MPmax (Smax). These parameters are functions of substrates and incubation conditions for a single species, and can be used for comparison between different species under the same conditions. The MPmax, Tmax, and KMP of the AAPB strain were quite different form those of the E. coli strain, and the AAPB strain was shown to be less sensitive to temperature and pH changes than the E. coli strain. KEY WORDS: Membrane potential · Flow cytometry · Bacteria · Cyanine dye · Physiology Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 37, No. 2. Online publication date: November 11, 2004 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2004 Inter-Research.

Homeoviscous and functional adaptations of mitochondrial membranes to growth temperature in soybean seedlings

The present study investigated whether the cold-sensitive character of soybean is reflected at the level of mitochondrial membranes. When exposed to an increase of temperature (from 25 to 35 ° C), mitochondrial membranes were characterized by a higher phosphatidylcholine : phosphatidylethanolamine ratio and a lower content in 18 : 3 fatty acid. After a reduction of temperature (from 25 to 18 ° ° ° C) the opposite changes were found. Lipid lateral diffusion and local microviscosity appeared to be comparable in mitochondria from plantlets grown at 25 or 35 ° C when assayed at the respective growth temperatures. Some functional aspects (cytochrome c oxidase activity or membrane conductance) tended to this behaviour whereas others (respiration rate or maximum membrane potential) did not. On the other hand, membranes from plants grown at 18 ° C were more rigid. Moreover, as illustrated by cytochrome c oxidase activity or respiration rate, functional measurements suggested that these membranes were less active at this temperature. Thus the dynamic characteristics and functional properties measured in mitochondrial membranes were in favour of an adaptive trend at 35 ° C, but not at 18 ° C despite changes in lipid composition, in accordance with the cold-sensitive character of the plant.

Factors affecting the susceptibility of sensitive yeast cells to killer toxin K1.

Optimum conditions for action of the killer toxin K1 on sensitive strain S. cerevisiae S6 were established. Maximum killing was reached in a very narrow pH range of 4.5-4.6. Maximum susceptibility to toxin was displayed by highly energized fresh cells from the early exponential phase in the presence of an external energy source (at least 200 mmol/L glucose). Further, maintenance of maximum membrane potential was necessary for killer action, as documented by decreasing toxin activity in the presence of increasing concentrations of KCl. The killing was strongly stimulated in the presence of millimolar concentrations of Ca2+ and Mg2+.

Atrial ectopic pacemaker escape mediated by phasic vagal nerve activity

Effects of vagal nerve activity on atrial ectopic pacemaker foci were studied in vitro in strips of rabbit tricuspid valve. Transmembrane potentials were recorded from pacemaker and working atrial fibers superfused with Tyrode solution containing propranolol. Tissues were paced from the atrial muscle end at cycle lengths of 90, 70, or 50% of the intrinsic pacemaker cycle, and postganglionic vagal nerve endings were stimulated with brief trains of pulses (200 Hz; 100-200 microseconds) through a second electrode near the pacemaker. Vagal trains scanning diastole hyperpolarized pacemaker and surrounding fibers to a maximum membrane potential of -74.7 +/- 1.8 mV (normal maximum diastolic potential = -75.5 +/- 1.6 mV) and elicited a period of inexcitability lasting 217.9 +/- 27.3 ms (drive cycle = 90% of pacemaker cycle). Inexcitability was evident at critical diastolic intervals where vagal input prevented atrial impulses from activating the pacemaker allowing spontaneous discharges to occur, i.e., escape, late in diastole. Besides inexcitability, incidence and timing of escape impulses were determined by cumulative effects of drive cycle length, vagal stimulus, and subthreshold electrotonic input on intrinsic pacemaker cycle. These data suggest that phasic vagal stimuli may transiently protect atrial ectopic pacemaker foci from conducted sinus impulses by rendering pacemaker and surrounding fibers inexcitable. In the setting of a long sinus (drive) cycle length, phasic vagal activity may result in spontaneous discharges manifest as late atrial premature beats.

Membrane potentials in reconstituted cytochrome c oxidase proteoliposomes determined by butyltriphenyl phosphonium cation distribution

Equilibration of the butyltriphenyl phosphonium (BTPP +) cation into cytochrome c oxidase reconstituted proteoliposomes was measured potentiometrically. The maximum membrane potential (Δψ) generated by oxidase activity was estimated to lie between −65 and −90 mV, vesicle interior negative, when internal BTPP + binding is taken into account. Formation of Δψ was completely prevented by valinomycin and carbonyl-cyanide- p-trifluoromethoxyphenylhydrazone but only 10% inhibited by levels of N′,N′-dicyclohexylcarbodiimide that abolish proton pumping by the oxidase. Δψ is thus maintained by at least one charge transfer process that does not involve proton movement. A nonlinear relationship was obtained between oxidase activity and steady-state Δψ. The value of Δψ estimated by BTPP + distribution was lower than that calculated using the optical probes safranine and a carbocyanine dye. Possible reasons for this discrepancy are discussed.

Tetrodotoxin-sensitive Na+ channels in isolated single cultured rat myocardial cells.

We studied the existence of tetrodotoxin (TTX)-sensitive fast Na+ channels in isolated single (verified by dye injection) myocardial cells compared with small multiple-cell groups from 1- to 3-day-old rat ventricles in cell culture. For single cells, average values were -63 mV maximum membrane potential, 32 mV overshoot, and 65 V/s maximum rate of rise of the action potentials (+Vmax). These values were comparable to values from groups of multiple (2-10) cells. TTX strongly depressed +Vmax dose dependently, with no difference between single and multiple cells. +Vmax was also decreased by lowering extracellular Na+ concentration but not by D 600 or lowering extracellular Ca2+ concentration. These results suggest that 1) isolated single cells possess TTX-sensitive fast Na+ channels, 2) culturing per se does not alter TTX sensitivity, and 3) TTX sensitivity is not modified by cell density.

Spontaneous electrical activity and interaction of large and small cells in cardiac ganglion of the crab, Portunus sanguinolentus

1. Semi-isolated preparations of the nine-celled cardiac ganglion of the crab, Portunus sanguinolentus, were studied electrophysiologically, using simultaneous recording from extracellular and two or three intracellular electrodes. Nine penetrations of small cells were achieved. 2. Three large (80 x 120 micron) cells lie near the anterior end of the 5-mm main trunk; two large and four small (less than 50 micron) cells at the posterior end. Large-cell axons pass along the main trunk and then exit to innervate cardiac muscle; small-cell axons do not leave the ganglion. 3. The semi-isolated ganglion produces spontaneous electrical activity organized into regularly patterned, rhythmic bursts of large- and small-cell impulses recurring at rates of 0.3-0.6/s and lasting 500-800 ms. Small impulse activity commences and ends each burst. Small cells fire trains during the burst, but impulses are not synchronized among them. Large-cell trains are synchronous, are at about one-half the frequency, and have fewer impulses than small-cell trains. 4. Intracellular recordings from small cells show a slow, pacemaker depolarization from a maximum membrane potential of -54 mV leading with only a slight inflection at ca. -50 mV to a depolarized plateau at ca. -40 mV; nonovershooting impulses are superimposed on this but cease before it repolarizes. Impulses, therefore, arise at a site distant from the soma and do not invade it. Deflections suggesting synaptic potentials are not seen. 5. Intracellular recordings from large cells show complex depolarizations corresponding to extracellularly recorded bursts. These represent excitatory postsynaptic potentials (EPSPs) corresponding with individual small-cell impulses, attenuated, non-overshooting spikes, and an underlying slow depolarization; usually no pacemaker depolarization is apparent between bursts. Chemically mediated transmission is probable for the EPSPs because they show delay, increase in amplitude with hyperpolarization, sometimes show facilitation, and are reduced in saline having one-third Ca, 3 x Mg. 6. EPSPs, impulses, and the slow depolarization occur synchronously among the large cells. Potentials recorded from posterior cells are attenuated and slower than those of the anterior cells. This is interpreted to reflect sites of occurrence more distant from the soma in the posterior than in the anterior cells. Impulses do not invade the somata. 7. Intracellular recordings from large-cell axons 4 mm from the soma show overshooting action potentials arising sharply from a base line. EPSPs are absent or highly attenuated and there is little underlying depolarization (less than 2 mV). 8. Current passing with electrodes intracellular to two cells has established directly that all large cells are electrotonically coupled and that an anterior cell and a small cell are coupled. Changes of burst rate during current passing into any large cell indicate that all large cells and small cells are electrotonically coupled. 9...

Effects of vagal stimulation on the pacemaker action potentials of carp heart

1. 1. Transmembrane action potentials from the sino-atrial valve of the carp heart with spontaneous activity have been recorded with intracellular electrodes. 2. 2. Vagal stimulation decreased the slope of slow depolarization during diastole and increased the maximum membrane potential with accompanying bradycardia. There was a slight change or none at all in the configuration of the pacemaker action potential in response to vagal stimulation, while the action potential in the nonpacemaker responded to vagal stimulation with a shortening in duration and with little or no change in the membrane polarization. Such effects of vagal stimulation were blocked by atropine. 3. 3. Inhibitory effects were also observed by application of acetylcholine to the carp heart. 4. 4. Adrenaline did not produce excitatory effects on the pacemaker activity of the sino-atrial valve of the carp heart.

THE PHYSIOLOGICAL SIGNIFICANCE OF INORGANIC LEVELS IN THE INTERNAL MEDIUM OF ANIMALS

Summary(i) Proceeding from a consideration of the non‐diffusible constituents of the cells, the sum of the electric charges thereon, the mean intracellular pH, and an optimum or maximum membrane potential, the inorganic levels of Na, K, H, HCO2 and CI can be interpreted as physiological requirements and HCO3 and CI concentrations in turn, assuming a necessary ventilation tension of CO2. (2) Omitting considerations of the membrane potential, or treating them as of secondary importance, the optimum pH value, and in turn the K and HCO3 concentrations, are theoretically deducible by an alternative method of wider implications. (3) Including the effects of contact with the solid bone salts the concentration of the inorganic phosphate ions and minimal values for Ca and Mg ionic concentrations may also be deduced.