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PubMed1992

Development of a new geometrical form of micropipette: electrical characteristics and an application as a potassium ion selective electrode.

Using a mix of thermal and anodic bonding together with microlithographic techniques, the safe transference of a Si3N4 film with a pore (diameter down to 1 micron) to a glass tube tip (external diameter 800 microns) was accomplished, yielding a new geometrical form of micropipette. Compared with conventional glass micropipettes the device has shown lower resistance, more stable capacitance (independent of the tip immersion depth), tip potential closer to that of a salt bridge, and a simplified filling process. Using this device as a potassium ion selective electrode (ISE), a faster response time ISE was achieved. These features indicate that the new device can advantageously substitute the conventional glass micropipettes when cell impalement is not required.

Electric Conductivity↗
PubMed1980

Immunohistochemical localization and vascular effects of vasoactive intestinal polypeptide in skeletal muscle of the cat.

Scattered vasoactive intestinal polypeptide (VIP)-immunoreactive nerves were found in the striated muscle of the hind limb of the cat, where they usually were associated with small blood vessels. VIP-immunoreactive nerves were also demonstrated in the sciatic nerve; after ligation an abundance of intensely immunoreactive VIP fibres were seen proximal to the ligation. Intraarterial infusion of VIP into isolated hind limb of the cat had dramatic effects on different sections of the vascular bed. Thus, VIP dilated the resistance vessels leading to a marked increment in muscle blood flow. VIP also relaxed the capacitance vessels causing regional pooling of blood; it increased the capillary surface area available for fluid exchange. Infusions of VIP at a dose of 8 microgram/min significantly inhibited the vasoconstriction, induced by electrical stimulation of the regional sympathetic nerves. It is suggested that local nervous release of VIP may act as a modulator of vascular tone in skeletal muscle.

Animals↗
PubMed1990

Dielectrophoretic spectra of single cells determined by feedback-controlled levitation.

In this paper we have utilized the principle of dielectrophoresis (DEP) to develop an apparatus to stably levitate single biological cells using a digital feedback control scheme. Using this apparatus, the positive DEP spectra of both Canola plant protoplast and ligament fibroblast cells have been measured over a wide range of frequencies (1 kHz to 50 MHz) and suspending medium conductivities (11-800 muS/cm). The experimental data thus obtained have been interpreted in terms of a simple spherical cell model. Furthermore, utilizing such a model, we have shown that various cellular parameters of interest can be readily obtained from the measured DEP levitation spectrum. Specifically, the effective membrane capacitance of single cells has been determined. Values of 0.47 +/- 0.03 muF/cm2 for Canola protoplasts and 1.52 +/- 0.26 muF/cm2 for ligament fibroblasts thus obtained are consistent with those determined by other existing electrical methods.

Cell Membrane↗
PubMed1999

Hydrophobic thickness of fluid planar monooleylglycerol membranes maximally thinned by inversed micellisation.

A procedure of making membranes of amphiphilic materials at the bottom of a U-shaped flexible plastic tube within an aqueous medium is described. The membranes were made sufficiently large in order for the annulus area to be neglected. Consequently the hydrophobic thickness of the membrane could be measured by a capacitance technique assuming the relative permittivity of the hydrophobic part of the bilayer. Introduction of an AC microvolt technique allowed manufacture of stable thick membranes by quenching the electroconstriction observed when DC electrical potentials in the millivolt range are used. By continuously monitoring the hydrophobic thickness and by use of the AC microvolt technique the membrane-thinning process by chemical means could be studied in isolation because the electroconstriction was quenched. The maximally thinned hydrophobic thickness of a monooleylglycerol membrane measured at 38 degrees C was found to be 25+/-1.2 A. Criteria and argumentation for maximal thinning of the membrane are put forward. A distinction between genuine and modified cholesterol was demonstrated to be possible by the described method.

Journal Article↗
PubMed2006

Noncontact dielectric friction.

Dielectric fluctuations are shown to be the dominant source of noncontact friction in high-sensitivity scanning probe microscopy of dielectric materials. Recent measurements have directly determined the friction acting on custom-fabricated single-crystal silicon cantilevers whose capacitively charged tips are located 3-200 nm above thin films of poly(methyl methacrylate), poly(vinyl acetate), and polystyrene. Differences in measured friction among these polymers are explained here by relating electric field fluctuations at the cantilever tip to dielectric relaxation of the polymer.

Electric Impedance↗
PubMed2000

Heart and lung support interaction--modeling and simulation.

Mechanical support of the lungs used to preserve life or during any kind of surgery may have an adverse effect on the cardiovascular system. Usually, positive pressure in alveoli diminishes lung perfusion, venous return and cardiac output. Positive pressure during the respiratory cycle is transfered into the thoracic space. The aim of this study was to assess how synchronization of the respirator with spontaneous breathing influences the distribution of pressure and ventilation in nonhomogeneous lungs and how it should influence hemodynamics. For this purpose a multicompartmental model of respiratory system mechanics was used in the electrical analog of a respirator-lung circuit, which enabled us to simultaneously simulate ventilatory support and spontaneous breathing. Mechanical properties of the respiratory system were modeled by lumped parameters: resistances and capacitances of constant values, independent of lung volume or inspiratory flow changes. A multicompartmental model of the respiratory system enabled us to simulate lung pathology characterized by non-homogeneity of the mechanical properties of the different parts of the lungs. The results of simulations presented in the paper enable us to conclude that lung volume increase, independent of the respirator-patient breathing synchronization, may be modeled as the increase in pulmonary vascular resistance and alveolar pressure increase, dependent on respirator-patient breathing synchronization, may be averaged by esophageous balloon measurements which show intrathoracic pressure changes.

Cardiovascular Physiological Phenomena↗
PubMed1998

Electrophysiology of the in situ contractile vacuole complex of Paramecium reveals its membrane dynamics and electrogenic site during osmoregulatory activity.

In the freshwater protozoan Paramecium multomicronucleatum, excess cytosolic water, acquired osmotically, is segregated and expelled to the cell exterior through the activity of the contractile vacuole complex. This process keeps the cell volume constant. The electrophysiological parameters of the organelle were measured in situ using a fine-tipped microelectrode inserted into the contractile vacuole, the exocytotic vesicle of the organelle to which the segregated fluid is transported before being expelled to the exterior. The input capacitance decreased markedly immediately before fluid expulsion and regained its previous value when fluid filling resumed after fluid expulsion. This change in the capacitance proved that the contractile vacuole became disconnected from its radial arms, which project from the vacuole, before fluid expulsion occurred and then reconnected with the arms after fluid expulsion. A positive electrical potential was recorded from the contractile vacuole only when it was connected to the radial arms. This implies that the electrogenic mechanism resides exclusively in the radial arms and supports the idea that the decorated spongiomes, V-type proton-pump-covered terminal tubules of the radial arms that end blindly in the cytosol, are electrogenic. The linear current­voltage relationship of the contractile vacuole membrane also implies that few voltage-activated ion channels are present in the membrane. To explain the movement of water into the contractile vacuole complex, we favour the hypothesis that the potential generated across the decorated spongiome membrane can be used to drive counter-anions from the cytosol into the lumen of the complex. The anions could then act as an osmolite to pull cytosolic water into the lumen of the organelle.

Journal Article↗
PubMed2004

A circuit simulation compatible surface acoustic wave interdigital transducer macro-model.

In the present work, a surface acoustic wave (SAW) interdigital transducer (IDT) has been modeled as a resistance-inductance-capacitance (RLC) network. The model includes the effects of metal shorting and energy storage at metal discontinuities, as well as an arbitrary polarity sequence of fingers. A C++ program generates the equivalent electrical circuit, which is directly simulated by Simulation Program with Integrated Circuit Emphasis (SPICE), a popular electrical circuit simulator. Simulations compare well with reported experimental results, validating the proposed model.

Letter↗
PubMed2004

Capacitive coupling of atomic systems to mesoscopic conductors.

We describe a technique that enables a strong, coherent coupling between isolated neutral atoms and mesoscopic conductors. The coupling is achieved by exciting atoms trapped above the surface of a superconducting transmission line into Rydberg states with large electric dipole moments that induce voltage fluctuations in the transmission line. Using a mechanism analogous to cavity quantum electrodynamics, an atomic state can be transferred to a long-lived mode of the fluctuating voltage, atoms separated by millimeters can be entangled, or the quantum state of a solid-state device can be mapped onto atomic or photonic states.

Journal Article↗
PubMed1992

Ethanol uncouples dentate granule neurons by increasing junctional resistance: a multineuronal system model approach.

The effects of an acute intoxicating concentration of ethanol (50 mM) on the electrotonic membrane properties of hippocampal dentate granule neurons were studied using a system model incorporating electrotonic coupling between neurons. Uncoupling of cells by other alcohols has been shown in several tissues. The system model allows a quantitative estimation of the changes in coupling and other neuronal electrotonic properties. The input impedance of a neuron was measured from the voltage decay of a short hyperpolarizing current pulse. An analytic expression of the input impedance has been written incorporating somatic, dendritic, and electrical coupling parameters. Using this particular current stimulation, the modelling results showed that ethanol selectively increased the junctional resistance by more than 2.5 times, hence uncoupling the neurons. A 30% increase in the final time-constant, tau 0, was also obtained from the voltage transient. Other parameters were not significantly affected. A neuronal model without electrotonic coupling to other neurons gave rise to physiologically impossible values for the membrane resistance and capacitance. With resistive and capacitive coupling in the model, uncoupling did not occur with ethanol. It is concluded that ethanol uncouples neurons by increasing the effective gap junctional resistance in dentate granule neurons.

Animals↗
PubMedDate not supplied

Co-release of endogenous ATP and noradrenaline from guinea-pig mesenteric veins exceeds co-release from mesenteric arteries.

1. The present study was designed to compare the overflow of sympathetic neurotransmitters of guinea-pig inferior mesenteric artery and mesenteric vein evoked by electrical field stimulation (EFS) with special emphasis on the simultaneous release of ATP and noradrenaline (NA). The stimulation-evoked overflow of ADP, AMP and adenosine was also evaluated. 2. Endothelium-denuded segments of inferior mesenteric arteries or veins were superfused in a small volume (200 microL)-chamber for EFS and subsequent detection of NA (HPLC- electrochemical detection) and adenine nucleotides and adenosine (HPLC-fluorescence detection) in samples of the superfusate. 3. Both arteries and veins responded to EFS (15 V, 4-16 Hz, 0.3 msec for 60 s) with overflow of ATP and NA in a tetrodotoxin (1 micromol/L)- and guanethidine (10 micromol/L)-sensitive manner. The EFS-evoked overflow of NA in veins exceeded the overflow of NA in arteries at all frequencies of stimulation, whereas the EFS-evoked overflow of ATP, ADP and AMP in veins exceeded the overflow of adenine nucleotides in arteries at 4 and 8 Hz but not at 16 Hz stimulation. The EFS-evoked overflow of adenosine was similar in arteries and veins. 4. Activation of alpha1-adrenoceptors with methoxamine (10 micromol/L) did not produce overflow of ATP. 5. Blockade of alpha1/alpha2-adrenoceptors with phentolamine (1 micromol/L) did not affect EFS-evoked overflow of ATP, ADP, AMP and adenosine. 6. It is concluded that overflow of ATP and NA from sympathetic nerves may constitute an effective mechanism in the complex balance between capacitance and resistance in splanchnic circulation.

Adenosine↗
PubMed1991

Dose dependence of glutaraldehyde-induced changes in the electrical properties of the amphibian skin.

The effects of the protein cross-linker glutaraldehyde (GA) on the transepithelial short-circuit current (Isc), conductance (Gt) and impedance of the isolated frog skin were investigated at GA concentrations between 0.1 and 10 mM, i.e. up to three orders of magnitude less than used in fixative procedures. Below 0.5 mM GA increases Isc, with large variations among preparata. Millimolar GA concentrations induce fairly reproducible irreversible inhibitions of Isc, which proceed for about 3 h. The rate of Isc decrease and the amplitudes of the initial drop and subsequent recovery depend on GA concentration in a sigmoidal dose-effect way, reaching saturation at 10 mM. At this GA concentration, Gt is increased up to 5 times the control value. Transepithelial impedance measurements confirm the decreases in epithelial resistance (Rm) and show significant increases in epithelial capacitance (Cm). Rm is diminished by 20% at 0.5 mM GA and by 75% at 10 mM GA, while Cm is maximally augmented by 55% at 2.5 mM GA. It is concluded that protein cross-linking by mild GA treatment is a convenient procedure for changing the electrical characteristics of epithelia.

Animals↗
PubMed1986

Electrical properties and response to noradrenaline of individual heart cells isolated from human ventricular tissue.

The analysis of the electrical properties and response to catecholamines of cardiac tissue is greatly simplified by the use of single cell preparations. In this study individual cells isolated from human ventricular tissue were used to estimate cellular sarcolemmal resistance and capacitance and to record the time course of the response to ionophoretically applied noradrenaline. The mean input capacitance of the cells is consistent with a surface membrane area of approximately 15,000 micron2 if the specific membrane capacitance is 1 microF X cm-2. This is larger than might be expected from the measured external dimensions of the cell and is compatible with the presence of surface membrane infoldings and caveolae. At membrane potentials close to -75 mV the mean cell input resistance was approximately 40 M omega, giving a specific membrane resistance of 6 omega X cm2 if mean membrane area is 15,000 micron2 and consistent with the assumption that the isolated cells have sealed intercalated discs under the experimental conditions used. Ionophoretically applied noradrenaline produced a pronounced prolongation of the plateau phase of the action potential, but this effect developed over many seconds. The slow onset of action is not compatible with the kinetics of free extracellular diffusion of catecholamine but may reflect molecular events that occur between noradrenaline binding to membrane receptors and the final cellular response. Under voltage-clamp conditions, the cells showed a time dependent inward current consistent with the rapid activation and decay of a sarcolemmal calcium conductance.

Action Potentials↗
PubMed1983

Effect of chronic electrical stimulation at low frequency on the passive membrane properties of muscle fibers from dystrophic mice.

It has been reported that chronic electrical stimulation at low frequency applied to dystrophic muscles has a beneficial effect. In this study, the effect of this treatment on the passive membrane properties of muscle fibers from dystrophic mice was followed. Cable properties were assessed by the two-microelectrodes DC method and spacial decay analysis. Earlier results showing a decrease in resting potential, an increase in input resistance and in specific membrane resistance in muscle fibers from dystrophic mice were confirmed. In addition, the specific membrane capacitance of these muscle fibers was found to be lower than normal. This suggests that the membrane properties of fibers from dystrophic muscles are similar to those of immature muscle fibers. Muscle fibers from dystrophic animals that were stimulated for 2 to 4 weeks had membrane properties similar to those from normal muscles. This indicates that electrical stimulation at low frequency for 2 to 4 weeks restores membrane properties of dystrophic muscle fibers to normal and we suggest that an appropriate pattern of stimulation induces the maturation of dystrophic muscle fibers.

Animals↗
PubMed1976

Alternating current studies of charge carrier transport in lipid bilayers. Pentachlorophenol in lecithin-cholesterol membranes.

Surface and interior electrical properties of lecithin-cholesterol bilayer membranes treated with the uncoupler pentachlorophenol have been determined on the basis of a.c. measurements over a wide range of frequencies (0.02 to 1000 kHZ). The method used depends on accurately determining the resistance of the aqueous solution in series with each individual membrane by extrapolating admittance data into infinite frequency. Loss tangent vs. frequency curves are corrected by subtracting out a loss contribution which is present in untreated membranes and is due, presumably, to dielectric relaxation. The results, which are useful below 100 kHZ, can be fitted to loss tangent curves computed for a three-element equivalent circuit consisting of frequency independent conductance-capacitance pairs, arranged in series to represent surface and interior properties of membranes. Interior conductances agree with net conductances obtained from d.c. measurements. The pH and concentration dependence of surface conductance is consistent with a scheme of transport in which a fixed number of surface binding sites are filled preferentially with neutral pentachlorophenol molecules, which in turn dissociate to supply protons to the aqueous phase. Surface capacitances range from 15 to 90 times that of interior capacitance and show a systematic increase with pentachlorophenol concentration at high pH, and a decrease with concentration at low pH.

Biological Transport, Active↗
PubMed1999

Transepithelial capacitance decrease reveals closure of lateral interspace in A6 epithelia.

A sine wave method was used to measure transepithelial capacitance (CT) at 4.1 kHz (CHFT ). Model calculations show that CHFT reflects the equivalent capacitance of the series arrangement of apical and basolateral membrane capacitance. Cell swelling induced by reducing the basolateral osmolality from 260 to 140 mosmol/kg H2O (NaCl or sucrose removal) transiently decreased CHFT. The decrease in CHFT (DeltaCHFT ) reached its maximum 30 s after the onset of cell swelling and a complete recovery of CHFT was attained within 3-4 min. DeltaCHFT could be diminished by manoeuvres that reduced the rate or amplitude of cell swelling, i.e. lowering the temperature or treatment with low concentrations of glutaraldehyde (0.025%). DeltaCHFT increased with the magnitude of the osmotic perturbation but saturated at large volume expansions. DeltaCHFT increased with culture time. Electron micrographs showed a clear correlation between time course of CHFT changes and the closure of the lateral interspace (LIS). A striking correlation between the occurrence of CHFT recovery and the ability of the cells to develop a regulatory volume decrease (RVD) was found: Gd3+ (0.5 mM) inhibited both phenomena. The frequency dependence of CT was obtained from impedance spectra recorded over the range of 4 Hz to 22 kHz. These data agree with model calculations in which the contribution of the access resistance to the lateral membrane was included. All observations are consistent with the idea that DeltaCHFT originates from the closure of the LIS during cell swelling. The latter phenomenon increases the access resistance to the lateral membrane, which results in a marked reduction of the basolateral membrane area detected at high frequencies with capacitance measurements.

Algorithms↗
PubMed2005

Label-free electrochemical DNA sensor based on functionalised conducting copolymer.

A simple and label-free electrochemical sensor for recognition of the DNA hybridization event was prepared based on a new functionalised conducting copolymer, poly[pyrrole-co-4-(3-pyrrolyl) butanoic acid]. This precursor copolymer can be easily electrodeposited on the electrode surface and shows high electroactivity in an aqueous medium. An amino-substituted oligonucleotide (ODN) probe was covalently grafted onto the surface of the copolymer in a one step procedure and tested on hybridization with complementary ODN segments. The cyclic voltammogram of ODN probe-modified copolymer showed very little change when incubated in presence of non-complementary ODN, while a significant, and reproducible, modification of the voltammogram was observed after addition of complementary ODN. The AC impedance spectrum showed an increased charge transfer resistance (Rct) and double layer capacitance of the sensor film after hybridisation. Sensors with thinner films showed higher sensitivity than thicker films, suggesting that hybridisation at or near the surface of the film produces a larger change in electrical properties than that within the body of the film.

Biosensing Techniques↗
PubMed2003

Limiting frequency of the cochlear amplifier based on electromotility of outer hair cells.

Outer hair cells are the critical element for the sensitivity and sharpness of frequency selectivity of the ear. It is believed that fast motility (electromotility) of these cells is essential for this function. Indeed, force produced by outer hair cells follows their membrane potential very closely at least up to 60 kHz. However, it has been pointed out that the cell's receptor potential is attenuated by a low-pass RC circuit inherent to these cells, with the RC roll-off frequencies significantly lower than their operating frequencies. This would render electromotility ineffective in producing force. To address this issue, we assume that multiple degrees of freedom and vibrational modes due to the complex structure of the organ of Corti provide optimal phases for outer hair cells' force to cancel viscous drag. Our derived frequency limit depends on the drag-capacitance product, not directly on the RC time constant. With a reasonable assumption for the viscous drag, the estimated limit is 10-13 kHz, exceeding the RC corner frequency. Our analysis shows that a fast-activating potassium current can substantially extend the frequency limit by counteracting the capacitive current.

Acoustic Stimulation↗