Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Electric Capacitance”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed2006

Dielectric properties of E. coli cell as simulated by the three-shell spheroidal model.

Dielectric properties of E. coli cell have been re-studied by means of the three-shell spheroidal model, where the three shells correspond to the outer membrane, the periplasmic space and the inner membrane, respectively. With the model, a curve-fitting procedure has been developed to analyze the dielectric spectra. Although E. coli cell has been studied before, its special morphological structure was taken into account more comprehensively than any previous model in the present work. Dielectric properties of various cell components have been estimated from the observed dielectric spectra, especially the permittivity of the outer membrane, which was evaluated quantitatively for the first time. The values of epsilon(om) were 12 for kappa(om) of 0 to 10(-4) S/m and 34 for kappa(om) of 10(-3) S/m. The specific capacitance of the inner membrane was 0.6-0.70 microF/cm(2). The relative permittivity and the conductivity of the cytoplasm were about 100 and 0.22 S/m, respectively, and the conductivity of the periplasmic space was 2.2-3.2 S/m.

Cell Membrane↗
PubMed2002

Sheet conductor model of brain slices for stimulation and recording with planar electronic contacts.

Current and voltage in a brain slice are considered, taking into account the boundary conditions at the surface to an electrolyte bath and at the substrate of an electron conductor. A sheet conductor model is introduced with ohmic leak conductance to the bath and capacitive coupling to the substrate. It assigns a current-source density of neuronal activity to extracellular field potentials recorded by planar contacts, and it relates the current of planar capacitive contacts to the field potential that elicits neuronal activity. Two examples are analytically solved: the recording across a layered brain slice and the stimulation by a circular electrode. The study forms the basis for neurophysical experiments with brain slices or retinae on microelectronic chips.

Action Potentials↗
PubMed2005

Auditory hair cell-afferent fiber synapses are specialized to operate at their best frequencies.

Auditory afferent fiber activity is driven by high-fidelity information transfer from the sensory hair cell. Presynaptic specializations, posited to maintain fidelity, are investigated at synapses with characteristic frequencies of 120 Hz and 320 Hz. Morphological data indicate that high-frequency cells have more synapses and higher vesicle density near dense bodies (DBs). Tracking vesicular release via capacitance changes identified three overlapping kinetic components of release corresponding to morphologically identified vesicle pools. High-frequency cells released faster; however, when normalized to release site number, low-frequency cells released faster, likely due to a greater Ca2+ load per synapse. The Ca(2+)-dependence of release was nonsaturating and independent of frequency, suggesting that release, not refilling, was rate limiting. A model of release derived from vesicle equilibration between morphologically defined pools reproduced the capacitance data, supporting a critical role in vesicle trafficking for DBs. The model suggests that presynaptic specializations enable synapses to operate most efficiently at their characteristic frequencies.

Animals↗
PubMed2006

Effects of Liuwei Dihuang decoction on ion channels and synaptic transmission in cultured hippocampal neuron of rat.

The effect of Liuwei Dihuang decoction (LW), a traditional Chinese medicine (TCM) prescription, on voltage-dependent currents and synaptic transmission were investigated in cultured hippocampal neurons of rat by whole-cell patch clamp recording technique. After application with serum from LW-treated rats, termed LW-containing serum (LWCS) for 48 h, the amplitude of delay rectifying K+ current (IK) and voltage-gated Ca2+ current (ICa) decreased. While the frequency of spontaneous excitatory post-synaptic current (sEPSC) and miniature excitatory post-synaptic current (mEPSC) increased significantly. Yet the amplitude of voltage-depended Na+ current (INa) and transient outward K+ current (IA), membrane capacitance and resistance remained unchanged. The results indicated that LWCS possessed the effect of modulating or improving neuronal and synaptic function, which possibly contribute to the cognition enhancing effect of LW.

Administration, Oral↗
PubMedDate not supplied

A multi-nano-dot circuit and structure using thermal-noise-assisted tunneling for stochastic associative processing.

The single-electron circuit and nanostructure described in this paper are designed for stochastic associative processing, which is an expanded version of ordinary associative memory processing. In stochastic associative processing, the association probability of each stored pattern depends on the similarity between the stored pattern and the input pattern. Such unique processing is useful for sequential stochastic association and for clustering for vector quantization. Conventional single-electron circuits operate only at very low temperature for practical junction capacitance (i.e., 30 K for 0.1 aF) because the charging energy in these circuits is directly related to the tunnel junction capacitance. Our multi-nano-dot circuit and structure operate at room temperature with a junction capacitance around 0.1 aF through tunneling processes assisted by thermal noise. We analyze the operation of this circuit in detail and propose for it a stochastic associative processing operation, where the detection timing of the electron position controls the association probability distribution.

Computer Simulation↗
PubMed2006

Implications of the negative capacitance observed at forward bias in nanocomposite and polycrystalline solar cells.

Four different types of solar cells prepared in different laboratories have been characterized by impedance spectroscopy (IS): thin-film CdS/CdTe devices, an extremely thin absorber (eta) solar cell made with microporous TiO2/In(OH)xSy/PbS/PEDOT, an eta-solar cell of nanowire ZnO/CdSe/CuSCN, and a solid-state dye-sensitized solar cell (DSSC) with Spiro-OMeTAD as the transparent hole conductor. A negative capacitance behavior has been observed in all of them at high forward bias, independent of material type (organic and inorganic), configuration, and geometry of the cells studied. The experiments suggest a universality of the underlying phenomenon giving rise to this effect in a broad range of solar cell devices. An equivalent circuit model is suggested to explain the impedance and capacitance spectra, with an inductive recombination pathway that is activated at forward bias. The deleterious effect of negative capacitance on the device performance is discussed, by comparison of the results obtained for a conventional monocrystalline Si solar cell showing the positive chemical capacitance expected in the ideal IS model of a solar cell.

Cadmium Compounds↗
PubMed2003

Strategies for improving neural signal detection using a neural-electronic interface.

There have been various theoretical and experimental studies presented in the literature that focus on interfacing neurons with discrete electronic devices, such as transistors. From both a theoretical and experimental perspective, these studies have emphasized the variability in the characteristics of the detected action potential from the nerve cell. The demonstrated lack of reproducible fidelity of the nerve cell action potential at the device junction would make it impractical to implement these devices in any neural prosthetic application where reliable detection of the action potential was a prerequisite. In this study, the effects of several different physical parameters on the fidelity of the detected action potential at the device junction are investigated and discussed. The impact of variations in the extracellular resistivity, which directly affects the junction seal resistance, is studied along with the impact of variable nerve cell membrane capacitance and variations in the injected charge. These parameters are discussed in the context of their suitability to design manipulation for the purpose of improving the fidelity of the detected neural action potential. In addition to investigating the effects of variations in these parameters, the applicability of the linear equivalent circuit approach to calculating the junction potential is investigated.

Action Potentials↗
PubMed2006

Field-effect sensors with charged macromolecules: characterisation by capacitance-voltage, constant-capacitance, impedance spectroscopy and atomic-force microscopy methods.

Field-effect-based capacitive electrolyte-insulator-semiconductor (EIS) sensors have been utilised for the deoxyribonucleic acid (DNA) immobilisation and hybridisation detection as well as for monitoring the layer-by-layer adsorption of polyelectrolytes (anionic poly(sodium 4-styrene sulfonate) (PSS) and cationic poly(allylamine hydrochloride) (PAH)). The EIS sensors with charged macromolecules have been systematically characterised by capacitance-voltage, constant-capacitance, impedance spectroscopy and atomic-force microscopy methods. The effect of the number and polarity of the polyelectrolyte layers on the shift of the capacitance-voltage curves has been investigated. Alternating potential shifts of about 30-90 mV have been observed after the adsorption of each polyanion and polycation layer, respectively. The DNA immobilisation and hybridisation signals were 35-55 and 24-33 mV, respectively. The possible mechanisms for the sensor responses are discussed.

DNA↗
PubMed2006

Measurement of intestinal edema using an impedance analyzer circuit.

BACKGROUND: Acute intestinal edema adversely affects intestinal transit, permeability, and contractility. Current resuscitation modalities, while effective, are associated with development of acute intestinal edema. Knowledge of levels of tissue edema would allow clinicians to monitor intestinal tissue water and may help prevent the detrimental effects of edema. However, there is no simple method to measure intestinal tissue water without biopsy. We sought to develop a tissue impedance analyzer to measure tissue edema, without the need for invasive biopsy. METHODS: Oscillating voltage input was applied to the analyzer circuit and an oscilloscope measured the voltage output across any load. Rats were randomized to three groups: sham, mild edema (80 mL/kg of NS resuscitation), and severe edema (80 mL/kg of NS resuscitation with intestinal venous hypertension). Intestinal edema was measured by wet-to-dry tissue weight ratio. Bowel impedance was measured and converted to capacitance using a standard curve. RESULTS: Acute intestinal edema causes a significant increase in bowel capacitance. This capacitance can be used to predict tissue water concentration. CONCLUSION: Using an impedance analyzer circuit, it is possible to measure intestinal edema reliably and quickly. This may prove to be a useful tool in the resuscitation of critically ill patients.

Acute Disease↗
PubMed2001

A common molecular machinery for exocytosis and the 'kiss-and-run' mechanism in chromaffin cells is controlled by phosphorylation.

Exocytosis and 'kiss-and-run' secretion coexist in chromaffin cells. Our findings suggest that these mechanisms are closely related, based on their common molecular machinery. Here we present a model that describes how chromaffin cells regulate catecholamine release by switching the mode of secretion between the two pathways, a process controlled by phosphorylation. Stimulation-dependent vesicle-plasma membrane interactions in chromaffin cells were analysed by simultaneous 'on-cell' capacitance and conductance measurements, a technique that allows the monitoring of single vesicles. Capacitance steps represent fusions of large dense-core vesicles with the plasma membrane, whereas capacitance flickers correspond to transient connections of the vesicle lumen with the extracellular space. All these events require the presence of extracellular calcium in millimolar concentrations. 'Kiss-and-run' type of release is enhanced by the kinase inhibitor staurosporine, which suggests that this secretion mode is regulated by protein phosphorylation. We also observed capacitance bursts, which most probably represent 'hot spots' of secretion and we found that 'kiss-and-run' is the prevalent mechanism during these episodes. The significance of 'kiss-and run' for neurohormone release is even higher at physiological temperature, because up to half of all secretion events are mediated by this mechanism.

Animals↗
PubMed2005

Kinetics of exocytosis is faster in cones than in rods.

Cone-driven responses of second-order retinal neurons are considerably faster than rod-driven responses. We examined whether differences in the kinetics of synaptic transmitter release from rods and cones may contribute to differences in postsynaptic response kinetics. Exocytosis from rods and cones was triggered by membrane depolarization and monitored in two ways: (1) by measuring EPSCs evoked in second-order neurons by depolarizing steps applied to presynaptic rods or cones during simultaneous paired whole-cell recordings or (2) by direct measurements of exocytotic increases in membrane capacitance. The kinetics of release was assessed by varying the length of the depolarizing test step. Both measures of release revealed two kinetic components to the increase in exocytosis as a function of the duration of a step depolarization. In addition to slow sustained components in both cell types, the initial fast component of exocytosis had a time constant of <5 ms in cones, >10-fold faster than that of rods. Rod/cone differences in the kinetics of release were substantiated by a linear correlation between depolarization-evoked capacitance increases and EPSC charge transfer. Experiments on isolated rods indicate that the slower kinetics of exocytosis from rods was not a result of rod-rod coupling. The initial rapid release of vesicles from cones can shape the postsynaptic response and may contribute to the faster responses of cone-driven cells observed at light offset.

Animals↗
PubMed2007

Electrochemical characterization of albumin protein on Ti-6AL-4V alloy immersed in a simulated plasma solution.

The effect of oxygen and albumin on the electrochemical behavior of a Ti-6Al-4V alloy immersed in a simulated inorganic plasma (SIP) solution was studied with a rotating-cylindrical electrode configuration to focus on the surface/electrolyte reactions. Potentiokinetic scans and electrochemical impedance spectroscopy have been used to characterize the interface by determining the passive current density and capacitance. For the polarization scans, an albumin addition of 37.7 mg/cm(3) to the SIP solution (oxygenated and unoxygenated) decreased the passive current density, indicating a lowering of the corrosive rate. The surface capacitance for the Ti-6Al-4V alloy immersed in a SIP solution averaged 13 microF/cm(2), which transformed after albumin addition (37.7 mg/cm(3)) from a potential independent behavior to the capacitance ranging from 23 to 6 microF/cm(2) with increasing potentials from -800 to 1500 mV(SCE), respectively, indicative of albumin adsorption. Within the same potential range and albumin addition to oxygenated solutions, the capacitances expanded slightly with a similar decreasing trend from 31 to 6 microF/cm(2), although the capacitance depicts an interaction between the hydrated passive film and the adsorbed albumin from -550 to 500 mV(SCE) in which the capacitance plateaued at 15 microF/cm(2). The hydrated porous oxide film results from the porous rutile layer reacting with H(2)O(2) formed as an intermediary component of oxygen reduction at the Ti-6Al-4V surface. The passive film-albumin interaction would affect the processing of titanium alloys in their surface preparation for biocompatibility, as well as determining the reactivity of titanium alloys to proteins.

Alloys↗
PubMed2002

Membrane dielectric changes indicate induced apoptosis in HL-60 cells more sensitively than surface phosphatidylserine expression or DNA fragmentation.

The specific membrane capacitance and conductivity of mammalian cells, which reflect their surface morphological complexities and membrane barrier functions, respectively, have been shown to respond to cell physiologic and pathologic changes. Here, the effects of induced apoptosis on these membrane properties of cultured human promyelocytic HL-60 cells are reported. Changes in membrane capacitance and conductivity were deduced from measurements of cellular dielectrophoretic crossover frequencies following treatment with genistein (GEN). The apparent specific cell membrane capacitance of HL-60 cells fell from an initial value of 17.6+/-0.9 to 9.1+/-0.5 mF/m(2) 4 h after treatment. Changes began within minutes of treatment and preceded both the externalization of phosphatidylserine (PS), as gauged by the Annexin V assay, and the appearance of a sub-G1 cell subpopulation, as determined through ethidium bromide staining of DNA. Treatment by the broad spectrum caspase inhibitor N-benzyloxycarbony-Val-Ala-Asp(O-methyl)-fluoromethyketone (zVAD-fmk) did not prevent these early cell membrane dielectric responses, suggesting that the caspase system was not involved. Although membrane conductivity did not alter during the first 4 h of GEN treatment, it rose significantly and progressively thereafter. Finally, as the barrier function failed and the cells became necrotic, it increased by many orders of magnitude. The effective membrane capacitance and conductivity findings serve to focus attention on the membrane as a site for early participation in apoptosis. In conjunction with our prior reports of the use of dielectric methods for cell manipulation and separation, these results demonstrate that dielectrophoretic technologies should be applicable to the rapid detection, separation, and quantification of normal, apoptotic, and necrotic cells from cell mixtures.

Apoptosis↗
PubMed2005

Membrane capacitance and conductance changes parallel mucin secretion in the human airway epithelium.

Measurement of the magnitude and kinetics of exocytosis from intact epithelia has historically been difficult. Using well-differentiated cultures of human bronchial epithelial cells, we describe the use of transepithelial impedance analysis to enable the real-time quantification of mucin secretagogue-induced changes in membrane capacitance (surface area) and conductance. ATPgammaS, UTP, ionomycin, and PMA induced robust increases in total cellular capacitance that were demonstrated to be dominated by a specific increase in apical membrane surface area. The UTP-induced increase in capacitance occurred in parallel with goblet cell emptying and the secretion of mucin and was associated with decreases in apical and basolateral membrane resistances. The magnitude and kinetics of the capacitance increases were dependent on the agonist and the sidedness of the stimulation. The peak increase in capacitance induced by UTP was approximately 30 mucin granule fusions per goblet cell. Secretagogue-induced decreases in apical membrane resistance were independent of exocytosis, although each of the secretagogues induced profound reductions in basolateral membrane resistance. Transepithelial impedance analysis offers the potential to study morphological and conductance changes in cultured human bronchial epithelial cells.

Adenosine Triphosphate↗
PubMed2006

Formaldehyde assay by capacitance versus voltage and impedance measurements using bi-layer bio-recognition membrane.

A novel formaldehyde sensitive biosensor based on bacterial formaldehyde dehydrogenase (FDH) as a bio-recognition element has been developed. The bio-recognition membrane had bi-layer architecture and consisted of FDH, cross-linked with albumin, and of the cofactor NAD at a high concentration level (first layer). The second layer was a negatively charged Nafion membrane, which prevented a leakage of negatively charged NAD molecules from the bio-membrane. As transducers, gold electrodes SiO(2)/Si/SiO(2)/Ti/Au and electrolyte-insulator-semiconductor Si/SiO(2) (EIS) structures have been used. Changes in capacitance and impedance properties of the bio-recognition membrane have been used for monitoring formaldehyde concentration in a bulk solution. It has been shown that formaldehyde can be detected within a concentration range from 1 microM to 20mM depending on the type of transduction used, with a detection limit of 1 and 100 microM for gold-based and EIS-based transducers, respectively.

Aldehyde Oxidoreductases↗
PubMed2004

Recapture after exocytosis causes differential retention of protein in granules of bovine chromaffin cells.

After exocytosis, chromaffin granules release essentially all their catecholamines in small fractions of a second, but it is unknown how fast they release stored peptides and proteins. Here we compare the exocytic release of fluorescently labelled neuropeptide Y (NPY) and tissue plasminogen activator from single granules. Exocytosis was tracked by measuring the membrane capacitance, and single granules in live cells were imaged by evanescent field microscopy. Neuropeptide Y left most granules in small fractions of a second, while tissue plasminogen activator remained in open granules for minutes. Taking advantage of the dependence on pH of the fluorescence of green fluorescent protein, we used rhythmic external acidification to determine whether and when granules re-sealed. One-third of them re-sealed within 100 s and retained significant levels of tissue plasminogen activator. Re-sealing accounts for only a fraction of the endocytosis monitored in capacitance measurements. When external [Ca2+] was raised, even neuropeptide Y remained in open granules until they re-sealed. It is concluded that a significant fraction of chromaffin granules re-seal after exocytosis, and retain those proteins that leave granules slowly. We suggest that granules vary the stoichiometry of release by varying both granule re-sealing and the association of proteins with the granule matrix.

Animals↗
PubMed2002

Changes in morphology and inward rectifier currents in human atrial myocytes depend on culture conditions.

Human atrial myocytes were cultured under systematically varied conditions in order to obtain stable cells for future gene manipulation. Transient (I(to)) and sustained outward current (I(so)), and voltage- and muscarinic receptor-activated inward rectifier K(+) currents (I(K1), I(K,ACh)) were measured in freshly isolated cells and after 5 days in culture. Myocytes were grown on polylysin or laminin in medium with or without 10 % serum (medium+S, medium-S). Cultured myocytes dedifferentiated to a greater extent in medium+S than medium-S, but independent of the chemical nature of the adherence surface. Apparent surface area increased in medium+S, whereas membrane capacitance declined under all culture conditions. I(to) of myocytes cultured in medium-S was increased. Myocytes grown on polylysin and laminin exhibited reduced I(K1) current density. Under all culture conditions, I(K,ACh) was attenuated with carbachol but hardly affected with sphingosine-1-phosphate as agonists. In conclusion, morphological and electrophysiological changes depended on serum in the culture medium rather than on adherence surface being coated with laminin or polylysin.

Acetylcholine↗
PubMed2005

Calcium gradients and exocytosis in bovine adrenal chromaffin cells.

The relationship between the localized Ca(2+) concentration and depolarization-induced exocytosis was studied in patch-clamped adrenal chromaffin cells using pulsed-laser Ca(2+) imaging and membrane capacitance measurements. Short depolarizing voltage steps induced Ca(2+) gradients and small "synchronous" increases in capacitance during the pulses. Longer pulses increased the capacitance changes, which saturated at 16 fF, suggesting the presence of a small immediately releasable pool of fusion-ready vesicles. A Hill plot of the capacitance changes versus the estimated Ca(2+) concentration in a thin (100 nm) shell beneath the membrane gave n = 2.3 and K(d) = 1.4 microM. Repetitive stimulation elicited a more complex pattern of exocytosis: early pulses induced synchronous capacitance increases, but after five or more pulses there was facilitation of the synchronous responses and gradual increases in capacitance continued between pulses (asynchronous exocytosis) as the steep submembrane Ca(2+) gradients collapsed. Raising the pipette Ca(2+) concentration led to early facilitation of the synchronous response and early appearance of asynchronous exocytosis. We used this data to develop a kinetic model of depolarization-induced exocytosis, where Ca(2+)-dependent fusion of vesicles occurs from a small immediately releasable pool with an affinity of 1-2 microM and vesicles are mobilized to this pool in a Ca(2+)-dependent manner.

Adrenal Medulla↗