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PubMed1998

Does stimulation of NaCl secretion in in vitro perfused rectal gland tubules of Squalus acanthias increase membrane capacitance?

NaCl secretion in rectal gland tubules (RGT) of Squalus acanthias requires the activation of Cl– channels in the luminal membrane. The RGT and its mechanism of activation are an early evolutionary paradigm of exocrine secretion. The respective Cl– channels probably resemble the shark equivalent of the cystic fibrosis transmembrane conductance regulator (CFTR). Activation of these Cl– channels occurs via cAMP. It has been hypothesized that the activation of CFTR occurs via exocytosis or inhibited endocytosis. To examine this question directly by electrical measurements we have performed whole-cell patch-clamp analyses of in vitro perfused RGT. NaCl secretion was stimulated by a solution (Stim) containing forskolin (10 µmol/l), dibutyryl-cAMP (0.5 mmol/l) and adenosine (0.5 mmol/l). This led to the expected strong depolarization and an increase in membrane conductance (G m). The membrane capacitance (C m) was measured by a newly devised two-frequency synchronous detector method. It was increased by Stim significantly from 5.00±0.22 to 5.17±0.21 pF (n=50). The increase in C m correlated with the increase in G m with a slope of 51 fF/nS. Next the effect of furosemide (500 µmol/l) was examined in previously stimulated RGT. Furosemide was supposed to inhibit coupled Na+2Cl–K+ uptake and to reduce cell volume but not membrane trafficking of Cl– channels. Furosemide reduced G m slightly (due to the fall in cytosolic Cl– concentration) and C m to the same extent by which Stim had increased it. Both changes were statistically significant, and the slope of ΔC m/ΔG m was similar to that caused by Stim. Inhibitors of microtubules or actin (colchicine, phalloidin and cytochalasin D added at 10 µmol/l to the pipette solution and dialysed for >10 min) did not alter cell voltage, G m or C m, nor did these inhibitors abolish the stimulatory effect of cAMP. These data suggest that the small C m changes observed with Stim reflect a minor cell volume increase and an ”unfolding” of the plasma membrane. The present data do not support the exocytosis/endocytosis hypothesis of cAMP-mediated activation of Cl– channels in these cells.

Adenosine↗
PubMed2005

Patch-clamp study reveals that the importance of connexin43-mediated gap junctional communication for ovarian folliculogenesis is strain specific in the mouse.

Genetic ablation of connexin37 (Cx37) or connexin43 (Cx43), the two gap junction proteins expressed by mouse ovarian granulosa cells, has been shown to result in impaired follicle development. We used patch-clamp techniques to evaluate quantitatively the contribution of these connexins to gap junctional intercellular communication (GJIC) among granulosa cells. The coupling conductance derived from a voltage step-induced capacitive current transient was used as a measure of GJIC in cultured granulosa cells. Using this method, we determined that the conductance of wild-type (84.1 +/- 28.6 nS; n = 6) and Cx37-deficient granulosa cells (83.7 +/- 6.4 nS; n = 11) does not differ significantly (P = 0.35), suggesting a limited contribution, if any, of Cx37 to granulosa cell coupling. In contrast, the conductance between granulosa cells of Cx43-deficient mice (2.6 +/- 0.8 nS; n = 5) was not significantly different from that of single, isolated wild-type granulosa cells (2.5 +/- 0.7 nS, n = 5; P = 0.83), indicating that Cx43-deficient granulosa cells were not electrically coupled. A direct measurement of transjunctional conductance between isolated granulosa cell pairs using a dual patch-clamp technique confirmed this conclusion. Interestingly, a partial rescue of folliculogenesis was observed when the Cx43-null mutation in C57BL/6 mice was crossed into the CD1 strain, and capacitive current measurement demonstrated that this rescue was not due to reestablishment of GJIC. These results demonstrate that folliculogenesis is impaired in the absence of GJIC between granulosa cells, but they also indicate that the severity is dependent on genetic background, a phenomenon that cannot be attributed to the expression of additional connexins.

Animals↗
PubMed1984

Electric-field exposure of persons using video display units.

Electric fields produced by a selection of video display units have been measured over a frequency range from DC to 1 MHz. The magnitude and the time variation of the electric fields were both recorded by means of a single broadband capacitive sensor located on the surface of a simple simulation of the human body. The electric field at a given location was found to be the sum of three discrete components, each having a different spatial and time variation. These components are produced by, respectively, the charged CRT screen, the flyback transformer, and the low-voltage circuitry. For the units tested, operator exposures are substantially below the limits of existing workplace guidelines.

Data Display↗
PubMed1983

Comparative vascular effects of stimulation continuously and in bursts of the sympathetic nerves to cat skeletal muscle.

Recent electrophysiological studies indicate that sympathetic vasoconstrictor fibre dicharge in vivo usually occurs in intermittent high frequency bursts, increased activity being established by raised intra-burst frequency or, more commonly, by shortened burst intervals. The present study describes the responses of the resistance and capacitance vessels in cat skeletal muscle to electrical vasoconstrictor fibre stimulation with characteristics simulating the discharge pattern in vivo. Stimulation in bursts (1 s duration) was applied either at varying intra-burst impulse rates (from 5 to 160 Hz) at constant burst interval (5 or 10 s), or at varying burst intervals (from 32 to 2 s) at constant intra-burst frequency (16 or 32 Hz). For comparison, continuous stimulation was made at rates from 0.5 to 16 Hz. Both types of burst stimulation were capable of evoking maintained constrictions in the resistance and capacitance vessels, graded in relation to the total number of impulses/unit time. Stimulation in bursts at varying intervals was as effective as continuous stimulation with maximal constriction reached at 32 Hz bursts at 4 s intervals. The responses to stimulation in bursts at varying impulse rates peaked at 40 Hz, higher intraburst frequencies being less effective, at least in the resistance vessels. The data suggests that the resistance and capacitance vessels are gradedly responsive to sympathetic discharge rates up to about 40 Hz provided excitation occurs in bursts and, that an effective control can be achieved especially by shortening the burst interval. Sympathetic firing in skeletal muscle may thus well exceed 10 Hz, previously believed to be the upper physiological discharge range.

Animals↗
PubMedDate not supplied

Conductivity of normal and pathological human erythrocytes (homozygous beta-thalassemia) at radiowave frequencies.

The conductivity of normal and homozygous beta-thalassemic erythrocyte suspensions has been measured over the frequency range from 5 KHz to 100 MHz in the temperature interval from 5 to 45 degrees C. The electrical parameters of the membrane, i.e., the capacitance CM and the conductance GM per unit surface have been calculated from an expression given by Hanai for the conductivity of a suspension of ellipsoidal particles covered with a shell. Some interesting differences between the normal and pathological state are evidentiated.

Electric Conductivity↗
PubMedDate not supplied

Patch-clamp capacitance measurements: new insights into the endocytic uptake of transferrin.

Since its introduction by Neher and Sakmann in 1976 the patch-clamp technique has been extensively used to study processes such as signalling and synaptic transmission, but also for monitoring endo- and exocytosis. Since biological membranes behave like electrical capacitors high-resolution measurements of membrane capacitance allow detection of small changes in membrane surface area that accompany exocytosis and endocytosis. We here describe our recent work on patch-clamp capacitance measurements in stably transfected HeLa cells expressing HFE, the hereditary hemochromatosis gene product, under the control of a tetracycline-sensitive promotor. By means of whole-cell and cell-attached techniques we were able to reveal transferrin-induced decreases in membrane capacitance reflecting increased endocytosis at the single cell level. Moreover, cell-attached recordings revealed significant alterations in the formation of single endocytic vesicles. Time-resolved measurements of cell membrane capacitance provide a new methodological approach to study the endocytic uptake of transferrin and its regulation by HFE, the hereditary hemochromatosis protein.

Cytoplasmic Vesicles↗
PubMed2003

A topographical study of mechanical and electrical properties of single myocytes isolated from normal guinea-pig ventricular muscle.

Major regional differences in the electrical properties of myocytes from ventricular muscle have been described previously, on the basis of samples taken from a maximum of three regions in each heart. In order to define the topographical basis for such differences, we studied the electrical and mechanical properties of single myocytes isolated from 20 regions throughout the ventricles in the normal guinea-pig heart. Single myocytes were isolated using an enzymatic dispersion method, and were studied under conditions that were close to physiological. Cell capacitance and action potentials were recorded using the switch-clamp technique, and cell length and evoked shortening were measured using a photodiode array system. In the left ventricular free wall, mid-myocardial cells were longer and had greater capacitative surface area than surface myocytes. There were transmural but not longitudinal differences in APD90 (action potential duration to 90% repolarization), with the longest APD90 in subendocardial and the shortest in subepicardial myocytes. We found a septum-left ventricular free wall-right ventricular free wall gradient, with the longest APD90 in the septum and the shortest in the right ventricular free wall. The regional distribution of APD90 was closely mirrored by relaxation time. Peak cell shortening was greater in subendocardial myocytes than in subepicardial myocytes in the left ventricular free wall, and in myocytes from the left side of the septum compared with the right. We concluded that the regional distribution of APD is closely and inversely related to the sequence of ventricular depolarization, and that the regional variations in cell shortening amplitude are related principally to reported regional variations in wall stress.

Action Potentials↗
PubMed2006

Peripheral electrosensory imaging by weakly electric fish.

Different species have developed different solutions to the problem of constructing a representation of the environment from sensory images projected onto sensory surfaces. Comprehension of how these images are formed is an essential first step in understanding the representation of external reality by a given sensory system. Modeling of the electrical sensory images of objects began with the discovery of electroreception and continues to provide general insights into the mechanisms of imaging. Progress in electric image research has made it possible to establish the physical basis of electric imaging, as well as methods to accurately predict the electric images of objects alone and as a part of a natural electric scene. In this review, we show the following. (1) The internal low resistance of the fish's body shapes the image in two different ways: by funneling the current generated by the electric organ to the sensory surface, it increases the fields rostrally, thus enhancing the perturbation produced by nearby objects; and by increasing the projected image. (2) The electric fish's self-generated currents are modified by capacitive objects in a distinctive manner. These modulations can be detected by different receptor types, yielding the possibility of "electric color." (3) The effects of different objects in a scene interact with each other, generating an image that is different from the simple addition of the images of individual objects, thus causing strong contextual effects.

Animals↗
PubMed2004

Improvement of surface acoustic wave gas and biosensor response characteristics using a capacitive coupling technique.

As for many other electronic devices and circuits, electrical contact to surface acoustic wave sensors is usually made using bonding wires. This technique is known to result in reliable contact under most conditions, but it does so with several disadvantages. First, electrical contact is not reversible, impeding replacement of sensor devices. Second, bonding wires are quite delicate and should not be exposed to high gas or liquid flows. Third, the presence of bonding wires may limit the potential to miniaturize a sensor housing or flow cell. Therefore, a capacitive coupling technique was developed to replace bonding wires. This permitted redesign of flow cells and sensor arrays, resulting in flow cell volumes of 80 microL to 60 nL. As a consequence, response times were reduced to 1-2 s in gas sensing and a few minutes in liquid sensing, respectively. At the same time, sensor devices can be easily replaced, and the system is less susceptible to malfunction.

Acoustics↗
PubMed1995

Optimisation of gene transfer into vascular endothelial cells using electroporation.

OBJECTIVES: We have examined the conditions required to obtain optimum transfection efficiencies for human umbilical vein endothelial cells by transduction with a plasmid conferring neomycin resistance. MATERIALS AND METHODS: Preliminary studies examined the effects of electric discharges using the Biorad Gene Pulser on endothelial cells. Post-electroporation, there was a significant decrease in cell survival with increasing voltages (100-400 volts; p = 0.03), capacitances [125-960 microFarads (microF); p = 0.02], number of electric pulses (1-2; p = 0.03) and decreasing cell concentrations (p = 0.01). The optimal cell concentration was 3 x 10(6) cells/ml. Transfection studies utilised the neomycin resistance expressing plasmid, pTCF; transfectants were selected with the neomycin analogue G-148. RESULTS: Electro-transfection was optimised with increasing voltages (p = 0.02) and capacitances (p = 0.01) using a single pulse. Optimal transfection was obtained using 400 volts with a capacitance of 960 microF using a single pulse; the median transfection efficiency was 10%. Transduced endothelial cells stably expressed the plasmid for 12 days and at least two cell passages. CONCLUSIONS: The results indicate that endothelial cells can be efficiently transduced by electroporation to stably express an introduced gene. This may have important implications in vascular surgery.

Cell Survival↗
PubMed1988

[Effect of structures of the ventral surface of the medulla oblongata on coupled vascular functions of the small intestine].

The effect of the ventrolateral medulla electrical stimulation of various intensity on resistance, capacitance and exchange functions was studied in the vascular bed of the small intestine. Brain activation with superliminal current applied to a point 2 mm rostral-wise of the middle of the twelfth cranial nerve rootlets has been shown to produce the strongest effect on the precapillary resistance of the vascular bed, whereas brain stimulation in a point 2 mm caudal-wise of this level produces a much stronger effect on the postcapillary small intestine resistance.

Animals↗
PubMed1993

Effect of stress on the membrane capacitance of the auditory outer hair cell.

The membrane capacitance of the outer hair cell, which has unique membrane potential-dependent motility, was monitored during application of membrane tension. It was found that the membrane capacitance of the cell decreased when stress was applied to the membrane. This result is the opposite of stretching the lipid bilayer in the plasma membrane. It thus indicates the importance of some other capacitance component that decreases on stretching. It has been known that charge movement across the membrane can appear to be a nonlinear capacitance. If membrane stress at the resting potential restricts the movement of the charge associated with force generation, the nonlinear capacitance will decrease. Furthermore, less capacitance reduction by membrane stretching is expected when the membrane is already extended by the (hyperpolarizing) membrane potential. Indeed, it was found that at hyperpolarized potentials, the reduction of the membrane capacitance due to stretching is less. The capacitance change can be described by a two state model of a force-producing unit in which the free energy difference between the contracted and stretched states has both electrical and mechanical components. From the measured change in capacitance, the estimated difference in the membrane area of the unit between the two states is about 2 nm2.

Animals↗
PubMed2003

Role of titania incorporated on activated carbon cloth for capacitive deionization of NaCl solution.

Adsorption isotherms of NaCl on activated carbon cloth (ACC) and titania-incorporated activated carbon cloth (Ti-ACC) under an electric field were investigated to deduce the role of titania in capacitive deionization (CDI) of NaCl. Electrosorption of NaCl on the ACC was significantly increased by titania incorporation, whereas its physical adsorption was considerably decreased, resulting in an improved performance of the Ti-ACC as a CDI electrode. Langmuir isotherms based on a localized and fixed amount of adsorption were suitable for the simulation of electrosorption and physical adsorption of ions on the ACC electrodes. The variances of q(m) and b of Langmuir isotherms with electric potential indicate increases in the number of ions per adsorption site and in electrosorption strength of ions by titania incorporation. A cyclic voltammetric study for ion adsorption on ACC electrodes confirms the reversibility between electrosorption and desorption of ions, regardless of titania incorporation.

Journal Article↗
PubMed1978

[Relationship between central and peripheral mechanisms in regulating capacitance vessels].

In acute experiments on cats, responses of the resistance and capacitance vessels of the spleen and hindlimbs to local electric stimulation of the medulla oblongata, of the sympathetic nerves, and pressor reflexes during different pressure of the venous outflow, were studied. No structures were revealed which could selectively affect the capacitance vessels. The bulbar structures affected both the resistance and the capacitance vessels. The reflex responses aof the pre- and post-capillary portions of the vascular bed could be different, the transmural pressure being one of the factors for dilatory responses of the capacitance vessels. The different responses of the capacitance vessels could occur on account of both local and central mechanisms, their participation, however, being unequal.

Animals↗
PubMed1985

The influence of transverse tubular delays on the kinetics of charge movement in mammalian skeletal muscle.

A model was developed to describe the kinetics of slow, voltage-dependent charge movement in the rat omohyoid muscle. To represent the electrically distributed nature of the transverse tubular system (t-system), we followed an approach similar to that described by Adrian and Peachey (1973 J. Physiol. [Lond.]. 235:103), and approximated the fiber with 12 concentric cylindrical shells. Incorporated into each shell were capacitative and conductive elements that represented the passive electrical properties of the t-system, and an element representing the mobile charge. The charge was assumed to obey a two-state scheme, in which the redistribution of charge is governed by a first-order reaction, and the rate constants linking the two states were assumed to depend on potential according to the constant field expression. The predictions of this "distributed two-state model" were compared with charge movements experimentally measured in individual fibers. For this comparison, first, the passive electrical parameters of the model were adjusted to fit the experimental linear capacity transient. Next, the Boltzmann expression was fitted to the steady state Q vs. V data of the fiber, thereby constraining the voltage dependence of the rate constants, but not their absolute magnitude. The absolute magnitude was determined by fitting the theory to an experimental charge movement at a single test potential, which in turn constrained the fits at all other test potentials. The distributed two-state model well described the rising and falling phases of ON, OFF, and stepped OFF charge movements at temperatures ranging from 3 to 25 degrees C. We thus conclude that tubular delays are sufficient to account for the rounded rising phase of experimental charge movements, and that it is unnecessary to postulate higher-order reaction schemes for the underlying charge redistribution.

Animals↗
PubMed1999

Single micro electrode dielectrophoretic tweezers for manipulation of suspended cells and particles.

Cells or particles in aqueous suspension close to a single capacitively coupled micro electrode (CCME) driven with high frequency electric fields experience dielectrophoretic forces. The effects near the CCME can be used for trapping and manipulation of single cells using externally metallised glass pipettes and might be used to develop a microscope based on force or capacitance measurements in conductive media.

Biotechnology↗
PubMed2002

A comparison of techniques to optimize measurement of voltage changes in electrical impedance tomography by minimizing phase shift errors.

In electrical impedance tomography, errors due to stray capacitance may be reduced by optimization of the reference phase of the demodulator. Two possible methods, maximization of the demodulator output and minimization of reciprocity error have been assessed, applied to each electrode combination individually, or to all combinations as a whole. Using an EIT system with a single impedance measuring circuit and multiplexer to address the 16 electrodes, the methods were tested on resistor-capacitor networks, saline-filled tanks and humans during variation of the saline concentration of a constant fluid volume in the stomach. Optimization of each channel individually gave less error, particularly on humans, and maximization of the output of the demodulator was more robust. This method is, therefore, recommended to optimize systems and reduce systematic errors with similar EIT systems.

Artifacts↗
PubMed2003

Electrical impedance scanning-application of this new technique for lymph node evaluation in children.

BACKGROUND: Precise assessment of lymph nodes is crucial to the choice of therapy and prediction of outcome in cases of malignancy. Electrical impedance scanning (EIS) is being experimentally investigated for potential use as a diagnostic tool for differentiation of malignant lesions. Malignancies show different electrical properties with changes in conductivity and capacitance that can be analysed by EIS. Using a TransScan TS-2000 (TransScan Medical, Migdal Ha'Emek, Israel, distributed by Siemens-Elema AB, Solna, Sweden), EIS has been used in various studies for the identification of breast cancer as well as for characterisation of superficial lesions. OBJECTIVE: To evaluate the reliability of EIS for classifying lymph nodes in a pediatric population with sonographically suspicious lesions and to prove its accuracy. MATERIALS AND METHODS: The study population consisted of 77 children (42 boys, 35 girls) aged 1.1-17.1 years. All EIS results were compared to either histopathological findings or long-term follow-up investigations. RESULTS: Sensitivity for malignancies using EIS was 75% and specificity was 87%. The negative predictive value was 93% and the positive predictive value was 60%. CONCLUSIONS: This study suggests the potential usefulness of EIS as an additional imaging modality for the differentiation of lymph-node diseases in children. The histopathological spectrum of malignant lymph node transformation in children compared to studies in adults, and the characteristic meltdown in inflammatory or granulomatous transformed nodes, pose challenges to differentiation based on sonographic evaluation, and also to EIS classification.

Adolescent↗