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PubMed2004

Giant lipid vesicles impaled with glass microelectrodes: GigaOhm seal by membrane spreading.

Giant unilamellar lipid vesicles could be perfect systems to study ion channels in the environment of lipid membranes with defined chemical and physical properties. Prerequisite for electrical measurements is an intravesicular electrical contact. We describe the impalement of giant lipid vesicles by glass micropipet electrodes with a tight seal. To avoid displacement or burst during impalement, the vesicles are immobilized in relaxed conditions by microscopic picket fences of polyimide. The outer surface of the pipets is selectively coated with silanes or polylysine. Structurally, the impalement is verified by ejecting a fluorescent solution out of the pipet. For electrical characterization, current pulses are applied to the pipet and voltage transients are recorded. The data are evaluated in terms of the capacitance and effective resistance of the membrane. Directly after impalement, we observe a seal resistance up to 1.2 GOmega that continuously decays within a period of up to 20 min until it suddenly disappears without burst of the vesicle. During impalement, a spreading of the vesicle membrane along the outer surface of the pipets is observed using a fluorescent membrane-bound dye. We assign the tight pipet-vesicle contact to spreading of the lipid bilayer by a rolling mechanism and the loss of resistance to micro- and macropores that are induced by the resulting membrane tension. Limitation of spreading is attempted with barriers on the pipet.

Electric Impedance↗
PubMedDate not supplied

Quantization of membrane potential generation by cytochrome c oxidase in small vesicles.

Proteoliposomes incorporating cytochrome c oxidase have been prepared by the cholate dialysis method and by sonication. Sonication produces multilamellar vesicles heterogeneous in size in contrast to a more uniform preparation of unilamellar vesicles produced by the dialysis procedure. Respiratory control in both preparations ranges between 4 and 8. From an electron microscopic analysis of proteoliposome size, the average electrical capacitance/vesicle for the dialyzed and sonicated preparations is calculated as 15 X 10(-18) F and 130 X 10(-18) F, respectively. These capacitance values would lead to a quantization of membrane potential generation by the enzyme at 77 mV/turnover for the dialyzed preparation and 9 mV/turnover for sonicated vesicles. It is argued that these differences can explain the dependence of H+ translocation on the number of turnovers of cytochrome c oxidase in dialyzed preparations in contrast to the lack of dependence on number of turnovers in sonicated preparations.

Electric Conductivity↗
PubMed2001

A novel approach for precise simulation of the EMG signal detected by surface electrodes.

We propose a new electromyogram generation and detection model. The volume conductor is described as a nonhomogeneous (layered) and anisotropic medium constituted by muscle, fat and skin tissues. The surface potential detected in space domain is obtained from the application of a two-dimensional spatial filter to the input current density source. The effects of electrode configuration, electrode size and inclination of the fibers with respect to the detection system are included in the transfer function of the filter. Computation of the signal in space domain is performed by applying the Radon transform; this permits to draw considerations about spectral dips and clear misunderstandings in previous theoretical derivations. The effects of generation and extinction of the action potentials at the fiber end plate and at the tendons are included by modeling the source current, without any approximation of its shape, as a function of space and time and by using again the Radon transform. The approach, based on the separation of the temporal and spatial properties of the muscle fiber action potential and of the volume conductor, includes the capacitive tissue properties.

Action Potentials↗
PubMed1989

Reconstitution of the lipid matrix of the outer membrane of gram-negative bacteria as asymmetric planar bilayer.

This paper is a report on the reconstitution of the lipid matrix of the outer membrane of Gram-negative bacteria as an asymmetric planar bilayer. This is the first time that a planar membrane is described, which consists on one side of a phospholipid (PL) mixture and on the other side of lipopolysaccharide (LPS). Therefore, strong emphasis is placed on a physical characterization of this membrane via its electrical properties. The membranes were prepared from spread monolayers or from vesicle-derived monolayers. Contrary to observations for symmetric phospholipid membranes, specific capacitances of (0.67 +/- 0.02) mu F.cm-2, breakdown voltages between 200 and 400 mV and specific conductances between 10(-8) and 2 x 10(-7) S.cm-2 were obtained independent of the preparation method. The LPS-containing membranes were stable up to 3 hr if they were formed and kept at temperatures above the hydrocarbon chain melting temperature of the LPS. For the specific capacitance, a dependence on the aperture radius was observed. This is explained by assuming a toroidal transition zone at the rim of the aperture. First results on the action of the pore-forming alpha-toxin from Staphylococcus aureus on bilayers of different composition demonstrate particular characteristics of this asymmetric bilayer system. The pore-formation rate is highest in symmetric phospholipid bilayers, considerably lower in asymmetric PL/LPS systems and fully inhibited in LPS/LPS systems.

Bacterial Toxins↗
PubMed1998

Effects of cetyltrimethylammonium bromide (CTAB) surfactant upon the dielectric properties of yeast cells.

The dielectric properties of yeast cells in the absence and presence of cetyltrimethylammonium bromide (CTAB) were investigated. The surfactant concentration range was between 0.0 and 1.0 mM. The experimental permittivity and conductivity spectra of frequency were analyzed by means of the two-shell electrical cell model (Irimajiri et al., Bull. Inst. Chem. Res., Kyoto Univ. 69 (1991) 421-438), and the electrical phase parameters of cells were subsequently evaluated. The cytoplasm conductivity and the conductivity of the vacuole interior decreased drastically by treating the cells with surfactant. The apparent capacitance of the plasma membrane increased systematically from 0.65 microF/cm2, for untreated cells, up to about 0.75 microF/cm2, at 0.3 mM CTAB. This growth was ascribed to the increase in the folding of the membrane surface associated with the surfactant-induced cell shrinkage. A further addition of the surfactant entailed a gradual decrease of the capacitance that was assigned to the membrane solubilization by the surfactant molecules. Within the accuracy of the data, the specific capacitance of the vacuole membrane was nearly constant (0.544+/-0.021 microF/cm2) over the whole surfactant concentration range. Also, the cytoplasm permittivity remained constant at 64.3+/-4.5.

Cell Membrane↗
PubMed1974

Electrical response to vibration of a lipid bilayer membrane.

The discovery and characterization of a vibration response in a black lipid bilayer membrane is the topic of this paper. An electrical vibration response is obtained when the membrane is under voltage clamp and a weaker, but significant, response is obtained under current clamp. The effect arises from an induced variation in the membrane capacitance. It is further shown that the capacitance variation arises from a change in the membrane area as the membrane undergoes drumhead vibration. Possible physiological significance in mechanoreception is discussed.

Cholesterol↗
PubMed2005

Effect of semen collection method on pre- and post-thaw Guirra ram spermatozoa.

In this study, we evaluated the potential effect of the method of recovery (artificial vagina or electroejaculation) on the production and quality of Guirra ram spermatozoa cryopreserved for the possible constitution of a sperm bank. In order to address this question, we evaluated the effect of semen collection method on fresh semen quality parameters, including: volume, concentration, production, microscopic analysis (abnormal sperm and intact apical ridge) and sperm motility parameters determined by CASA system. For frozen-thawed semen, we evaluated motility parameters by CASA and intact apical ridge, acrosomal status, assessed by dual staining by IP and FITC-PNA and capacitation status, assessed by M540 and Yo-pro1, using flow cytometry. The main findings from this study were: (i) that electroejaculation resulted in a lower recovery efficiency (80% of the cases), as a consequence of contamination with urine or lack of response to the electrical stimulation; (ii) the fresh seminal quality was not significantly different between recovery methods, except for the concentration of spermatozoa, but total number of spermatozoa and the consequent number of possible seminal doses for artificial insemination were similar; and, (iii) a higher number of stable and functional spermatozoa (higher number of live non-capacitated cells, higher live acrosome intact cells and live acrosome reacted cells) were found for frozen-thawed spermatozoa collected by electro ejaculation than by artificial vagina. According to our results, we are able to develop both methodologies in the creation of the Guirra sperm bank. Assuming the advantages and limitations of both methodologies, in Guirra breed, would enable the rapid constitution of a sperm bank including samples from a large number of non-trained rams in a short period of time, which will increase the genetic variability, and so guarantee the conservation of this breed.

Acrosome↗
PubMed1987

Modifications in membrane properties of trigeminal sensory neurons during general anesthesia.

1. The effects of general anesthesia on passive and active membrane properties of trigeminal root ganglion neurons of decerebrate guinea pigs have been determined using frequency-domain analyses of small-amplitude perturbations of membrane voltage. Quantification of the effects was accomplished by fitting the complex impedance locus diagrams computed from the neuronal responses with a membrane model based on linearized Hodgkin-Huxley-like equations. 2. Endotracheal administrations of isoflurane (2-3% for periods of 30-180 s), the most extensively studied of five general anesthetics, did not elicit large changes in membrane potential or in electrical properties in 26 of the 38 neurons. In this relatively unresponsive group, application of isoflurane in higher concentrations (3-4%) tended to evoke small but significant changes (less than 20%) in membrane properties without altering membrane potential by greater than 5 mV. These changes consisted of increases in the effective input capacitance and input conductance. 3. The impedance magnitude functions were reduced in amplitude consistently in 12 of the 38 neurons during induction of general anesthesia with isoflurane (2-4%) or, in several cases, with halothane (2%). Such applications evoked depolarizations of 8-32 mV, which also were observed in several instances of anesthesia with enflurane and cyclopropane. Quantification of these effects on electrical properties by curve fitting with the linearized Hodgkin-Huxley model revealed increases in the effective input capacitance, in the time-invariant resting conductance, Gr, and in the voltage- and time-dependent conductance, GL. Sometimes, an initial decrease preceded the increase of Gr, and the relaxation time constant associated with GL usually was reduced by the anesthetic agent in the 12 neurons. 4. In 10 neurons, membrane resonance behavior (which was apparent as a large hump at low frequencies of the impedance magnitude functions) was reduced in amplitude, as well as broadened in bandwidth, when peak changes in membrane properties were evident, i.e., during surgical or deep anesthesia. These actions of isoflurane or halothane were correlated to a reduction in spike electrogenesis and they may account for the reduced tendency of neurons to fire repetitive action potentials during anesthesia with isoflurane or halothane.(ABSTRACT TRUNCATED AT 400 WORDS)

Anesthesia, General↗
PubMed2000

Compound exocytosis in voltage-clamped mouse pancreatic beta-cells revealed by carbon fibre amperometry.

Capacitance measurements of exocytosis were combined with carbon fibre amperometry for time-resolved measurements of the properties of secretion in single, insulin-secreting, mouse pancreatic beta-cells pre-loaded with the amine serotonin (5-HT). Glucose-induced electrical activity was associated with the appearance of brief and transient amperometric currents reflecting the serotonin co-released with insulin. The integrated amperometric responses resulting from voltage-clamp depolarisations were proportional to the corresponding increase in cell capacitance. Both parameters exhibited U-shaped relationships to the membrane potential with maximums around 0 mV. There was a variable latency (40-730 ms, average 230 ms) between the onset of the depolarisation and the amperometric current. During high-frequency repetitive stimulation, a progressive decrease in the exocytotic capacity ("depression") was observed. This was paralleled by a corresponding reduction of the amperometric responses. Using the carbon fibre to map the beta-cell for release sites indicated that exocytosis was confined to the part of the cell containing the highest density of secretory granules. Two types of amperometric responses were observed. In about 50% of the cells, a smooth increase was observed with no discernible discrete events. In the remaining cells, the amperometric records contained large spikes. These were ten or more times larger than that expected for the fusion of individual secretory granules. We propose that these large spikes reflect the exocytosis of multigranular complexes formed inside the beta-cell prior to exocytosis.

Action Potentials↗
PubMed2002

SNAREs in opposing bilayers interact in a circular array to form conducting pores.

The process of fusion at the nerve terminal is mediated via a specialized set of proteins in the synaptic vesicles and the presynaptic membrane. Three soluble N-ethylmaleimide-sensitive factor (NSF)-attachment protein receptors (SNAREs) have been implicated in membrane fusion. The structure and arrangement of these SNAREs associated with lipid bilayers were examined using atomic force microscopy. A bilayer electrophysiological setup allowed for measurements of membrane conductance and capacitance. Here we demonstrate that the interaction of these proteins to form a fusion pore is dependent on the presence of t-SNAREs and v-SNARE in opposing bilayers. Addition of purified recombinant v-SNARE to a t-SNARE-reconstituted lipid membrane increased only the size of the globular t-SNARE oligomer without influencing the electrical properties of the membrane. However when t-SNARE vesicles were added to a v-SNARE membrane, SNAREs assembles in a ring pattern and a stepwise increase in capacitance, and increase in conductance were observed. Thus, t- and v-SNAREs are required to reside in opposing bilayers to allow appropriate t-/v-SNARE interactions leading to membrane fusion.

Aluminum Silicates↗
PubMed1991

Analysis of the interaction between an MRI coil and a heterogeneous sample.

A theoretical analysis of the interaction between a magnetic resonance imaging radio frequency coil and a heterogeneous sample consisting of two conducting regions separated by a non-conducting membrane is presented. The effect of the capacitive coupling between the two regions is treated. Expressions are obtained for the power dissipation in the sample and the electrical impedance of the coil and an equivalent electrical circuit which models the interaction is presented. The sample power dissipation in this case lacks the usual quadratic dependence on frequency observed with homogeneous samples. Results of the analysis are shown to agree well with observation in an experimental coil-sample system.

Magnetic Resonance Imaging↗
PubMedDate not supplied

Isolated systolic hypertension from a vascular point of view.

Due to the results of antihypertensive intervention studies, isolated systolic hypertension (ISH) has gained new interest lately. Yet, apart from increased aortic stiffness, the specific pathophysiological features of ISH have remained largely undetermined. Therefore, we investigated the elastic properties of the vascular bed of an upper arm segment in uncomplicated ISH patients and matched normotensive controls using an electrical bioimpedance technique. Compared with the controls, the compliance of the arterial bed as a whole at normotensive blood pressure level was on the average 108.0% higher (p < 0.005) in the hypertensive patients. The blood volume of the arterial bed as a whole at operating blood pressure level and that of the larger arteries were significantly higher (40.5%, p < 0.05, and 40.5%, p < 0.01, respectively). The same held true for the venous blood volume (64.4%, p < 0.05), and for the width of the arterial compliance-pressure relation (34.6%, p < 0.01). We concluded that ISH is a separate pathophysiological entity in which all parts of a peripheral vascular bed are changed and the decreased buffering function of the aorta and large arteries is partly compensated for by an increase in small artery compliance.

Aged↗
PubMed1996

Tolerance of oocyte plasma membrane to electric current changes after fertilisation.

The tolerance of the oocyte plasma membrane (oolemma) to electrical pulses (TEP) was investigated for oocytes, zygotes, and embryos at the early and late 2-cell stage. The oocyte survival rate after two electrical pulses (1.4 kV/cm for 640 microns each) was used as an indicator of the TEP of the oolemma. Survival rate of mid-pronuclear zygotes (94.3% +/- 2.3%) was significantly (p < 0.05) higher than that of recently ovulated (2.1% +/- 1.9%) and in vivo aged (25.1% +/- 2.6%) oocytes; survival rate of in vivo aged oocytes was also significantly higher than that of recently ovulated oocytes. Soon after fertilisation, the survival rate of the oocytes markedly increased, up to 94% at the mid-pronuclear stage. Survival rate dropped thereafter. These results suggest that the characteristics of the oocyte plasma membrane (oolemma) change after fertilisation.

Animals↗
PubMed2003

Long-range electrostatic forces on the surfaces of aluminum oxide and silica oxide.

The morphology and electrical microstructure of different anodic oxide films on aluminum and thermic oxide on surface p-type silica (KDB/100) were studied using atomic force microscopy and scanning capacitance microscopy. It was shown that the small basic element in the texture of both thin (0.05 microm) and thick (0.8 microm) oxide films represents a disklike element ('grain') approximately 200x200x30 nm in size. For films with a rough surface relief, the capacitance (and consequently, the surface potential) shows strong fluctuations in the vicinity of coarse (approximately 5-8 microm) pores. Because of this, the image of the surface obtained using atomic force microscopy does not coincide with that obtained by scanning capacitance microscopy (the opposite contrast effect). The manifestation of the opposite contrast correlates with an increase in the surface potential of the anodic oxide films measured by an independent method. A series of experiments under atmospheric conditions at different distances from the end of the cantilever to the surface of anodic oxide films showed that the influence of the surface field is detectable at long distances (up to 0.7 microm). It was shown that at a test temperature of 120 degrees C, the opposite contrast disappears: the images obtained in the semicontact (atomic force microscopy) and non-contact (scanning capacitance microscopy) modes coincide with each other. The results obtained suggest a relationship between the formation of electrostatic nanosized irregularities at the surface of oxide films and the sorption of water molecules under atmospheric conditions.

Aluminum Oxide↗
PubMed1976

Determination of exposure to electric fields in extra high voltage substations.

Electrophysical effects related to extra high voltage are surveyed for the determination of the exposure of personnel to electric fields in substations. It is concluded that the electric field strengths and the electrical discharges to the personnel are the important electrophysical factors. Instruments for measuring the field strength at grounded surfaces and at nonzero potentials were constructed. Results are presented of measurements with these instruments in substations. A dummy was used for the measurement of the distribution of capacitive currents to a man. The dummy can also be used for measuring the effectiveness of special shielding clothes.

Accidents, Occupational↗
PubMed1989

Capacitance compensation and bridge balance adjustment in intracellular recording from dendritic neurons.

Under most experimental conditions in intracellular recording, the proper adjustment of the amplifier is essential for the interpretation of the signals recorded from neurons. It is considered possible to accurately align the capacitance compensation and bridge balance adjustments of the amplifier simultaneously with the recording of membrane potential of an impaled cell if a number of conditions are met. In the strictest sense, these conditions are met only if: (1) the neuron is isopotential and if its electrical behavior can be adequately described using a single exponential decay constant, and if (2) that decay time constant is much longer than that of the microelectrode. These conditions cannot usually be satisfied. Because intracellular adjustment of capacitance compensation and bridge balance is necessary in many circumstances, it is desirable, to know whether any of the methods for performing these adjustments are accurate when used under less strict constraints, and to assess the nature and degree of the error that can be expected when the constraints are ignored. The results of computer simulations of a simple intracellular recording amplifier, microelectrode and a dendritic neuron model consisting of an isopotential cell and terminated finite equivalent cylinder representation of the dendrites are presented here. These studies show that the introduction of fast components of the response to intracellular current transients by the redistribution of applied charge in dendrite neurons may sometimes make it impossible to correctly apply the conventional methods of capacitance compensation and bridge balance. If the high-frequency response of the intracellular recording amplifier has sufficient fidelity, however, these adjustments can be made to a sufficient degree of accuracy using the response to sine wave calibration signals of varying frequency.

Computer Simulation↗
PubMed1989

Measurement of perception threshold to an electric stimulus using a phase-sensitive technique in normal and diabetic subjects.

To evaluate the functional state of peripheral sensitivity we measured the perception threshold to an electrical stimulus applied deeply at the level of the lower limbs in both diabetic and nondiabetic patients. The data were obtained using a phase-sensitive technique with a sinusoidal applied voltage at 1592 Hz. The test signal applied through needle electrodes was monitored using a current-to-voltage convertor, the current being considered to have two components, one resistive (IR) in phase with the voltage V across the electrodes, and the other capacitive (IC) 90 degrees out of phase. A significantly (p less than 0.001) higher perception threshold was found in diabetic patients than in nondiabetic subjects with all three electrical variables measured: IR, IC and V.

Adolescent↗