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 901 records · Page 50Linked to original sources
PubMed2003

Plasmon-waveguide resonance and impedance spectroscopy studies of the interaction between penetratin and supported lipid bilayer membranes.

The interaction between the cell-penetrating peptide, penetratin, and solid-supported lipid bilayer membranes consisting of either egg phosphatidylcholine (PC) or a 75/25 mol% mixture of egg PC and palmitoyloleylphosphatidylglycerol has been studied by simultaneously measuring plasmon-waveguide resonance (PWR) spectra and impedance spectra of lipid-peptide mixtures. When penetratin was incorporated into an egg PC + palmitoyloleylphosphatidylglycerol bilayer, PWR measurements showed a hyperbolic increase in the average refractive index and the refractive index anisotropy, with no change in membrane thickness, over a concentration range between 0 and 2 micro M peptide. In the case of an egg PC bilayer, a biphasic dependence was observed, with a decrease in average refractive index and anisotropy and no thickness change occurring between 0 and 5 micro M peptide, and an increase in membrane thickness occurring between 5 and 15 micro M peptide with no further change in the refractive index parameters. For both membranes, the impedance spectroscopy measurements demonstrated that the electrical resistance was not altered by peptide incorporation, whereas a decrease in membrane capacitance occurred with the same concentration dependence as observed in the PWR experiments, although for the PC membrane no further changes in electrical properties were observed in the higher concentration range. A structural interpretation of these results is described, in which the peptide binds electrostatically within the headgroup region of the bilayer and influences the headgroup conformation, amount of bound water, and the lipid-packing density, without perturbing the hydrocarbon core of the bilayer.

Carrier Proteins↗
PubMed1996

A mathematical model of the crustacean stretch receptor neuron. Biomechanics of the receptor muscle, mechanosensitive ion channels, and macrotransducer properties.

1. A mathematical model of the primary transduction process in a mechanoreceptor, the slowly adapting stretch receptor organ of the crayfish, has been developed taking into account the viscoelastic properties of the accessory structures of the receptor, i.e., the receptor muscle, the biophysical properties of the mechanosensitive channels (MSCs) and the passive electrical properties of the neuronal membrane (leak conductance and capacitative properties). The work is part of an effort to identify and characterize the mechanical and ionic mechanisms in a complex mechanoreceptor. The parameters of the model are based mainly on results of our own experiments and to some extent on results from other studies. The performance of the model has been compared with the performance of the slowly adapting receptor. 2. The model resulted in nonlinear differential equations that were solved by an iterative, fourth order Range-Kutta method. For the calculations of potential, the cell was treated as an idealized spherical body. The extension of the receptor muscle was 0-30%, which is within the physiological limits for this receptor. 3. The mechanical properties of the receptor muscle were modeled by a simple Voigt element (a spring in parallel with a dashpot) in series with a nonlinear spring. This element can describe resonably well the tension development in the receptor muscle at least for large extensions (> 12%). However, for small extensions (< 12%), the muscle seems to be more stiff than for large extensions. 4. The receptor current at different extensions of the receptor was computed using typical viscoelastic parameters for a receptor muscle together with a transformation of muscle tension to tension in the neuronal dendrites and finally the properties of the mechanosensitive channels. The model fit was satisfactory in the high extension range whereas in the low extension range the deviation from the experimental results could be explained partly by insufficient modeling of the nonlinear viscoelastic properties. The voltage dependence of the receptor current was also well predicted by the model. 5. If the parameters of the viscoelastic model were adjusted for each extension so that each tension response closely resembled the experimental values, the fit of the current responses was improved but still deviated from the experimental currents. One factor that might explain the difference is the possibility that the MSCs in the stretch receptor neuron might have intrinsic adaptive properties. Introducing an exponential adaptive behavior of individual MSCs increased the ability of the model to predict the receptor current. 6. The receptor potential was calculated by modeling the neuronal membrane by a lumped leak conductance and capacitance The calculated receptor potential was higher than the experimental receptor potential. However, the fit of the receptor potential was improved substantially by introducing an adaptation of the MSCs as outlined in the preceding paragraph. the remaining discrepancy might be explained by insufficient blocking of K+ channels in the experiment. 7. The model can predict a wide range of experimental data from the slowly adapting stretch receptor neuron including the mechanical response of the receptor muscle, the receptor current and its voltage dependence, and the receptor potential. It also describes accurately the passive electrical properties of the neuronal membrane.

Adaptation, Physiological↗
PubMed1968

Electrical signs of new membrane production during cleavage of Rana pipiens eggs.

Rana pipiens eggs dividing normally in diluted Ringer's solution show an increase in transmembrane potential inside negative, a decrease in resistance, and no change in total surface membrane capacitance at the appearance of a division furrow. Furrows of eggs in solutions with the tonicity of full Ringer develop partially, then regress so that the surface is again spherical. The potential and resistance changes are greater and substantial increases in capacitance occur when furrowing is so inhibited. It is proposed that the electrical changes at division are due to the introduction of new plasma membrane, between the blastomeres, having selective permeability to K and a low resistance compared to the outer spherical membrane. A narrow gap between blastomeres limits current flow through new membrane during normal division. A direct exposure of new membrane to the bathing medium when furrowing is disrupted results in larger changes in potential and resistance and permits the capacitance of new membrane to be detected.

Animals↗
PubMed1981

Effect of chronic ethanol exposure on the electric membrane properties of DRG neurons in cell culture.

Neural cell cultures of adult mouse dorsal root ganglia were utilized to investigate the effects of chronic ethanol exposure on neuronal electric membrane properties (EMP). After 12 days of exposure to various ethanol concentrations, the EMP of the neurons were determined in ethanol-free medium. Significant changes in a number of EMP were observed. Of particular physiological significance were decreased specific membrane resistance, increased specific membrane capacitance, relatively little change in membrane time constant, and increased electrical excitability. Various features of the action potential were also affected, e.g., reduced overshoot, afterhyperpolarization, and rate of rise. In preliminary experiments, EMP were determined at varying periods after the cultures had been withdrawn from ethanol medium and maintained in ethanol-free medium. These results indicated that the altered EMP persisted as long as one (Cm) to two (Rm) weeks after ethanol withdrawal. A possible mechanism for these ethanol-induced changes in EMP was suggested, utilizing the membrane expansion theory of anesthesia. Because of few previous reports demonstrating significant electrophysiological effects of ethanol at pharmacological concentrations, the neural cell culture system provides a useful new experimental model for studying the action of chronic ethanol exposure on neuronal EMP and the physical basis of the tolerance and withdrawal phenomena found in alcoholism and addiction in general. After being maintained for 12 days in culture media containing various concentrations of ethanol, non-neuronal cell survival was observed to have decreased in an approximately linear manner with increasing ethanol levels. By contrast, neuron survival was not affected until ethanol concentrations greater than 0.34 g % were used. This decreased cell survival due to chronic exposure to physiological levels of ethanol has not been reported previously. Neural cell cultures may therefore be useful for investigating the cellular pathology of chronic alcoholism and fetal alcohol syndrome.

Animals↗
PubMed1993

Pre-steady-state charge translocation in NaK-ATPase from eel electric organ.

Time-resolved measurements of charge translocation and phosphorylation kinetics during the pre-steady state of the NaK-ATPase reaction cycle are presented. NaK-ATPase-containing microsomes prepared from the electric organ of Electrophorus electricus were adsorbed to planar lipid bilayers for investigation of charge translocation, while rapid acid quenching was used to study the concomitant enzymatic partial reactions involved in phosphoenzyme formation. To facilitate comparison of these data, conditions were standardized with respect to pH (6.2), ionic composition, and temperature (24 degrees C). The different phases of the current generated by the enzyme are analyzed under various conditions and compared with the kinetics of phosphoenzyme formation. The slowest time constant (tau 3(-1) approximately 8 s-1) is related to the influence of the capacitive coupling of the adsorbed membrane fragments on the electrical signal. The relaxation time associated with the decaying phase of the electrical signal (tau 2(-1) = 10-70 s-1) depends on ATP and caged ATP concentration. It is assigned to the ATP and caged ATP binding and exchange reaction. A kinetic model is proposed that explains the behavior of the relaxation time at different ATP and caged ATP concentrations. Control measurements with the rapid mixing technique confirm this assignment. The rising phase of the electrical signal was analyzed with a kinetic model based on a condensed Albers-Post cycle. Together with kinetic information obtained from rapid mixing studies, the analysis suggests that electroneutral ATP release, ATP and caged ATP binding, and exchange and phosphorylation are followed by a fast electrogenic E1P-->E2P transition. At 24 degrees C and pH 6.2, the rate constant for the E1P-->E2P transition in NaK-ATPase from eel electric organ is > or = 1,000 s-1.

Animals↗
PubMed1989

Autonomic nervous control of nasal vasculature and airflow resistance in the anaesthetized dog.

1. In pentobarbitone-anaesthetized dogs with constant-flow vascular perfusion of nasal mucosa on both sides, nasal airway resistance, vascular resistance, vascular capacitance (via changes in total venous outflow) and blood flow in the anterior and posterior venous systems were measured. 2. Electrical stimulation of the cut peripheral ends of the cervical sympathetic trunk, caudal nasal nerve, or major palatine nerve increased vascular resistance and decreased vascular capacitance and airway resistance. Propranolol and atropine had no effect on the responses while bretylium completely abolished them; phentolamine greatly lessened the vascular resistance response and partially decreased the vascular capacitance and airway responses. Hence, sympathetic stimulation causes constriction of the resistance vessels via alpha-adrenergic mechanism and constriction of capacitance vessels via alpha-adrenergic as well as some non-adrenergic and non-cholinergic mechanisms. 3. Denervation of the cervical sympathetic trunk, caudal nasal nerve and major palatine nerve decreased nasal vascular resistance and increased vascular capacitance and airway resistance, suggesting tonic sympathetic discharge to nasal mucosa via caudal nasal and major palatine nerves. 4. Electrical stimulation of the nerve of pterygoid canal decreased vascular resistance but increased vascular capacitance (in the posterior venous system) and airway resistance to low-voltage stimulation (below 10 V), and decreased vascular capacitance (in the anterior venous system) and airway resistance to high-voltage stimulation (above 10 V). Hexamethonium reversed the vascular resistance response as well as vascular capacitance and airway responses to high-voltage stimulation. Bretylium and phentolamine enhanced the vascular resistance response and reversed vascular capacitance and airway resistance responses to high-voltage stimulation. Hence, low-voltage stimulation results in parasympathetic dilatation of resistance and capacitance vessels whereas high-voltage stimulation results in parasympathetic dilatation of resistance vessels and sympathetic constriction of capacitance vessels. The parasympathetic vasodilatation was atropine resistance and the sympathetic vasoconstriction was partially via alpha-adrenergic mechanisms. 5. Denervation of the nerve of pterygoid canal did not affect vascular resistance, vascular capacitance or airway resistance suggesting negligible tonic parasympathetic and sympathetic discharges to nasal blood vessels via the nerve. 6. Simultaneous optimal stimulation of sympathetic and parasympathetic nerves resulted in vasoconstriction, especially in capacitance vessels, suggesting sympathetic predominance over parasympathetic control.

Airway Resistance↗
PubMed1977

Neuronal mechanisms for object discrimination in the weakly electric fish Eigenmannia virescens.

The peripheral sensory basis for object discrimination was investigated in the weakly electric fish Eigenmannia virescens. Single unit recordings were made from the primary afferent fibres in the posterior branch of the anterior lateral line nerve while the local electric field (self-generated and stimulated) was modified by external resistance and capacitance shunts. Both fibre types (probability and phase coders) responded differentially to capacitance and resistance shunts of equivalent impedence. The degree of response differentiation between the two shunting conditions varied with the intensity of the electrical stimulus at the receptor. These data suggest that the primary electroreceptors can discriminatively encode the two electrical characteristics of 'objects'. However, since the response of primary electroreceptors also varied with the spatial orientation of the shunting electrodes, central structures must play an important role in object discrimination.

Action Potentials↗
PubMedDate not supplied

The perception threshold to an electric stimulus deeply applied in the lower limbs in normal and diabetic subjects.

The loss of sensitivity to nociceptive stimuli is one of the main factors involved in the pathogeny of diabetic gangrene. The aim of this study was to develop a simple and practical method for selecting the cases prone to such a complication. The perception threshold (either voltage, mV or current, microA) was determined in 137 randomly selected diabetic patients and 38 non-diabetic controls, by an original electronic device using sinusoidal waves, delivered through two electrode needles introduced at a depth of 0.5 cm at two points located on the anterior aspect of the shank about 12 cm apart. At each of the eight frequencies studied (10, 20, 50, 100, 200, 500, 1000 and 2000 Hz) three electrical parameters (voltage across the needle electrodes, the resistive and the capacitive current component) were recorded when the subject first perceived the stimulus. A significantly higher perception threshold was found in diabetic patients vs. non-diabetic subjects, at all frequencies studied and with all three electrical parameters recorded. A greater difference in the perception threshold between diabetic and non-diabetic subjects (a ratio higher than 3) was, however, found using the resistive component of the current and at frequencies higher than 200 Hz.

Adolescent↗
PubMed1997

Observations on rheological, electrical, and optical changes during rigor development in pork and beef.

Electrical and optical changes were measured in bovine sternomandibularis and porcine sternocephalicus strips tested sinusoidally in a rigorometer up to 3 h postmortem. Rigor development was detected by decreased muscle elongation, decreased stress-strain hysteresis area, and increased elastic modulus. Elastic modulus was affected by loading rate (r = .98, P < .005) from loading rates of 3.6 to 13.3 kPa/s. Capacitance decreased and resistance increased at 120 Hz, 1 kHz, and 10 kHz as rigor developed. Sometimes changes were irregular at one frequency but steady at another. The most consistent electrical predictors of rigor development were capacitance at 120 Hz and resistance at 10 kHz. Electrical impedance changed as muscle strips were stretched in the rigorometer, so that dimensional effects could be a source of error if testing causes muscle contraction. The dominant fiber-optic reflectance changes during rigor development were increases toward 400 nm and decreases toward 700 nm, although transient increases were sometimes detected toward 700 nm. Optical changes generally were later than electrical changes. All these complex changes are an obstacle to the early prediction of pH-dependent aspects of meat quality from electrical and optical measurements.

Abattoirs↗
PubMed2004

The role of voltage gated T-type Ca2+ channel isoforms in mediating "capacitative" Ca2+ entry in cancer cells.

The mechanism by which Ca2+ enters electrically non-excitable cells is unclear. The sensitivity of the Ca2+ entry pathway in electrically non-excitable cells to inhibition by extracellular Ni2+ was used to direct the synthesis of a library of simple, novel compounds. These novel compounds inhibit Ca2+ entry into and, consequently, proliferation of several cancer cell lines. They showed stereoselective inhibition of proliferation and Ca2+ influx with identical stereoselective inhibition of heterologously expressed Cav3.2 isoform of T-type Ca2+ channels. Proliferation of human embryonic kidney (HEK)293 cells transfected with the Cav3.2 Ca2+ channel was also blocked. Cancer cell lines sensitive to our compounds express message for the Cav3.2 T-type Ca2+ channel isoform, its delta25B splice variant, or both, while a cell line resistant to our compounds does not. These observations raise the possibility that clinically useful drugs can be designed based upon the ability to block these Ca2+ channels.

Calcium↗
PubMed2000

Participation of phospholipase A2 isoforms in the control of calcium influx into electrically non-excitable cells.

The participation of phospholipase A2 isoforms in capacitative store-operated Ca2+ influx into Jurkat leukemic T and MDCK cells was investigated. Preincubation of Jurkat cells with either bromophenacyl bromide (an inhibitor of secreted phospholipase A2, sPLA2) or Helss (an inhibitor of calcium independent phospholipase A2--iPLA2) resulted in a significant inhibition of the calcium influx. The extent of this inhibition depended on the pH of the extracellular millieu; it increased with alkalisation. The rate of Ca2+ influx into MDCK cells was reduced by bromophenacyl bromide. Preincubation of these cells with Helss resulted in the stimulation of the influx. These observations suggest the participation of different PLA2 isoforms in the regulation of Ca2+ influx. They also show that the extent that PLA2 isoforms control the influx depends on the pH of the medium. Finally, these data indicate that various phospholipase A2 isoforms may play a role in the control of Ca2+ influx in different cell lines.

Acetophenones↗
PubMed2003

A new computational approach for electrical analysis of biological tissues.

A new computational approach for electrical analysis especially designed for application in biological tissues is presented. It is based on the modelling of the electrical properties of the medium by means of lumped circuit elements, such as capacitance, conductance and current sources. The cell scale model is suitable for modelling the local anisotropy around cell membranes. It permits to obtain the electric potential, ionic concentrations and current densities around cells in time steps in an iterative process. The tissue scale model utilises volume-averaged values of conductivity and permittivity and models suitably the dispersive characteristic of biological tissues. It permits to obtain potential and current distributions in large volumes of tissue in the time or frequency domain. An example of analysis of skeletal muscle is presented aiming to demonstrate the features of the method.

Animals↗
PubMed1979

Whole body transvascular filtration coefficient and interstitial space capacitance.

Infusion experiments with Ringer's solution were performed on 5 splenectomized dogs with continuous monitoring of blood volume and hematocrit. The plasma volume was calculated from these data and followed during the infusion and also during the recovery period. Applying electrical equivalent simulation analysis to the result of the plasma volume, the capacitance of the interstitial fluid space and the transvascular filtration coefficient of water in the whole body were determined simultaneously. The mean values of the capacitance and the coefficient were 5.91 ml/kg-mmHg and 0.314 ml/min-kg-mmHg, respectively. From this simulation study, a transfer function which predicts the fluid shift between the vascular system and the interstitial fluid space was also derived. Using the transfer function, predictions of the changes in plasma volume are possible from any given rate of infusion.

Animals↗