Effects of mesencephalic stimulation on resistance and capacitance vessels in extremity of the dog.
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Animals↗
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Results for “Electric Capacitance”
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Capacitance responses and fluid exchange in the cat liver.
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Animals↗
A cleft model for cardiac Purkinje strands.
Conduction of the action potential in cardiac muscle is complicated by its multicellular structure, with narrow intercellular clefts and cell-to-cell coupling. A model is developed from anatomical data to describe cardiac Purkinje strands of variable diameter and different internal arrangements of cells. The admittance of the model is solved analytically and fit to results of cable analysis. Using the extracted specific membrane and cell electrical parameters (Rm = 13 K omega cm2, Cm = 1.5 mu F/cm2, Ri = 100 mu cm, and Re = 50 omega cm), the model correctly predicted conduction velocity and filling of capacitance at the onset of a voltage step. The analysis permits more complete studies of the factors controlling conduction velocity; for instance, the effect on conduction velocity of a capacity in the longitudinal current circuit is discussed. Predictions of the impedance and phase angle were also made. Measurements of the frequency dependence of phase angle may provide a basis for separating cleft membrane properties from those of the surface membrane and may aid the measurement of nonlinear membrane properties in muscle.
Action Potentials↗
Electric field driven protonation/deprotonation of self-assembled monolayers of acid-terminated thiols.
Using electrochemical impedance spectroscopy (EIS), we provide an explanation for the pH dependence of the voltammetric peak height for the electric-field-driven protonation and deprotonation of carboxylic acid-terminated thiol self-assembled monolayers (SAMs). The current flowing through the interface can be divided into a purely capacitive current and a protonation/deprotonation current that is directly related to the rate of change of the SAM's protonation (or deprotonation). We demonstrate that at applied potentials close to those corresponding to half-ionization of the SAM and pHs near the pK(1/2), the equivalent circuit describing the interface consists of a Helmholtz film capacity in parallel with a "protonation/deprotonation" impedance which is further shown to be a series combination of a resistor, Rp, and capacitor Cp. Explicit expressions for Rp and Cp are derived in terms of the rate constants for the forward (protonation) and reverse (deprotonation) reactions. Simulated EIS data demonstrate the agreement between our model of the interface and experimental impedance and voltammetric data.
Journal Article↗
Amperometric detection of quantal secretion from patch-clamped rat pancreatic beta-cells.
Serotonin (5-HT) is taken up in insulin granules and co-released with insulin on stimulation of pancreatic islet beta-cells. Based on these observations, we have used microcarbon fiber amperometry to examine secretogogue-induced 5-HT release from rat beta-cells preloaded for 4-16 h with 5-HT and then exposed to a bath solution containing 10 microM forskolin. In response to local application of KCl (60 mM) or tolbutamide (50-200 microM), we recorded barrages of amperometric events. Each amperometric event consisted of a short pulse of current measurable at electrode voltages that catalyze 5-HT oxidation. With either secretogogue, release was calcium-dependent. On combining amperometry with perforated patch whole-cell recording, we found that barrages of such events were well coupled in time and graded in intensity with depolarization-induced Ca2+ currents and well correlated with increases in membrane capacitance. In cell-attached patch recording, amperometric events evoked by application of tolbutamide followed the closure of ATP-sensitive K+ channels and coincided with the onset of electrical activity. These experiments suggest that amperometry is a useful technique for studying, in real time, the dynamic aspects of stimulus-secretion coupling in beta-cells. Their performance was facilitated by the design of a new carbon fiber electrode (ProCFE) described within.
Animals↗
Ripening of Nectarine Fruit (Changes in the Cell Wall, Vacuole, and Membranes Detected Using Electrical Impedance Measurements).
Electrical impedance measurements were used to characterize changes in intracellular and extracellular resistance as well as changes in the condition of membranes during ripening of nectarines (Prunus persica [L.] Batsch cv Fantasia). These measurements were related to changes in fruit texture assessed by flesh firmness and apparent juice content. An electrical model indicated that, during ripening (d 1-5) of freshly harvested fruit, the resistance of the cell wall and vacuole declined by 60 and 26%, respectively, and the capacitance of the membranes decreased by 9%. Accurate modeling of the impedance data required an additional resistance component. This resistance, which declined by 63% during ripening, was thought to be associated with either the cytoplasmic or membrane resistance. Changes in tissue resistance measured using low frequencies of alternating current were closely related to flesh firmness. After storage at 0[deg]C for 8 weeks, the nectarines developed a woolly (dry) texture during ripening at 20[deg]C. The main difference between these chilling-injured nectarines and fruit ripened immediately after harvest was the resistance of the cell wall, which was higher in woolly tissue (4435 [omega] after 5 d at 20[deg]C) than in nonwoolly tissue (2911 [omega] after 5 d at 20[deg]C). The results are discussed in relation to physiological changes that occur during the ripening and development of chilling injury in nectarine fruit.
Journal Article↗
A capacitance ultrasonic transducer for high-temperature applications.
This paper introduces a novel ultrasonic capacitance transducer for operation at elevated gas temperatures of several hundred degrees Celsius. The transducer design is based on a metallic membrane foil and a backplate made of an electrically conducting substrate coated with an insulation layer. Guidelines are given for selecting suitable materials for the membrane foil, the backplate substrate, and the coating. Manufacturing techniques applied for fabrication of different transducer types are described in detail. Transducers tested were composed of titanium substrates with insulation layers of silicon nitride or of silicon substrates with silicon oxide coatings. Experimental setup and test procedures are described. Results of transducer characterization and performance tests at elevated temperatures are presented and discussed. Transducer functionality is proven for air temperatures of up to 500 degrees C.
Journal Article↗
Reduction in acetylcholine sensitivity of axotomized ciliary ganglion cells.
1. Isolated cell clusters from ciliary ganglia of 3- to 4-day-old chickens were used to examine the electrical characteristics and sensitivity to iontophoretically applied acetylcholine (ACh) of normal cells and cells that had been axotomized on the day of hatching. 2. Resting potentials, input resistances and capacitances were the same in axotomized cells as in normal cells. These averaged about 70 mV, 165 Momega and 35 pF respectively. 3. Sensitivity to iontophoretically applied ACh was lower in axotomized cells than in normal cells by a factor of about 8. The rise times of the ACh potentials were the same in the two groups; indicating that the reduced sensitivity was not due to a diffusion barrier. 4. The slopes of the dose-reponse curves, plotted on a double-logarithmic scale, suggested that the co-operative action of two ACh molecules was involved in activating a post-synaptic conductance channel. This relation was unaltered by axotomy. 5. The estimated reversal potential for the action of ACh was unchanged after axotomy. 6. Cells in isolated clusters were similar to those in intact ganlia with respect to threshold depolarization, amplitude and time course of action potentials and ability to generate repetitive action potentials. There were no differences in these characteristics between normal and axotomized cells. 7. Cells in the isolated clusters had input resistances which were larger by a factor of 2-3 and capacitances that were smaller by a factor of about 2 than those of cells in intact ganglia. It is suggested that these differences were due to loss of initial segments of axons from the isolated cells. 8. Normal cells in the isolated clusters displayed spontaneous miniature synaptic potentials, indicating that synaptic integrity was maintained during the isolation procedure. As in intact ganglia, no spontaneous activity was observed in axotomized cells.
Acetylcholine↗
Electrically induced flows in the vicinity of a dielectric stripe on a conducting plane.
We report a theoretical and experimental study of the hydrodynamic flow induced by an a.c. electric field in the vicinity of a dielectric stripe deposited on a conducting plate. In the theoretical part, we model the stripe as a small change of the surface capacitance of the plate, and a perturbative approach is used to perform the calculations. This approach predicts an outwards rectified electro-osmotic slip along the surface that generates two steady counter-rotating rolls, the size of which decreases with the frequency. In the experimental section, we use tracers to determine the structure of the flow and investigate its dependence on the frequency and the amplitude of the applied voltage. The structure and amplitude of the observed flow compares satisfactorily with the theoretical analysis. This could guide the design of surface-controlled flows and help to understand the collective behavior of colloids near electrodes.
Journal Article↗
[The possibilities of hyperthermia from an engineering standpoint].
The possibilities of hyperthermia are discussed from the engineering technology standpoint. Microwave equipment yields powerful effects against a superficial tumor. RF capacitive method and annular phased array system (APAS) are typical heating methods against a deep-seated tumor. We have proposed that in the RF capacitive method the diameter of the applicator electrode should be more than 1.5 times the distance between two electrodes. In APAS another exciting method (TE mode) has been proposed. Electric current flows through the short axis of the body by the TE mode excitation. We are developing re-entrant resonant cavity applicators which have the characteristics to heat cylindrical regions of small diameter. We can install an x-ray tube inside the re-entrant electrode. This method is suitable for deep and concentrated heating. We conclude that the recent rapid development of various kinds of hyperthermia apparatus makes it possible to heat more safely and effectively the deep-seated regions of the human body.
Biomedical Engineering↗
Quantification of membrane properties of trigeminal root ganglion neurons in guinea pigs.
Passive and active (voltage- and time-dependent) membrane properties of trigeminal root ganglion neurons of decerebrate guinea pigs have been determined using frequency-domain analyses of small-amplitude perturbations of membrane voltage. The complex impedance functions of trigeminal ganglion neurons were computed from the ratios of the fast Fourier transforms of the intracellularly recorded voltage response from the neuron and of the input current, which had a defined oscillatory waveform. The impedance magnitude functions and corresponding impedance locus diagrams were fitted with various membrane models such that the passive and active properties were quantified. The complex impedances of less than one-quarter of the 105 neurons which were investigated extensively could be described by the complex impedance function for a simple RC-electrical circuit. In such neurons, the voltage responses to constant-current pulses, using conventional bridge-balance techniques, could be fitted with single exponential curves, also suggesting passive membrane behavior. A nonlinear least-squares fit of the complex impedance function for the simple model to the experimentally observed complex impedance yielded estimates of the resistance of the electrode, and of input capacitance (range, 56 to 490 pF) and input resistance (range, 0.8 to 30 M omega) of the neurons. The majority of trigeminal ganglion neurons were characterized by a resonance in the 50- to 250-Hz bandwidth of their impedance magnitude functions. Such neurons when injected with "large" hyperpolarizing current pulses using bridge-balance techniques showed membrane voltage responses that "sagged" (time-dependent rectification). Also, repetitive firing commonly occurred with depolarizing current pulses; this characteristic of neurons with resonance in their impedance magnitude functions was not observed in neurons with "purely" passive membrane behavior. A nonlinear least-squares fit of a five-parameter impedance fitting function based on a membrane model to the impedance locus diagram of a neuron with resonance yielded estimates of its membrane properties: input capacitance, the time-invariant part of the conductance, the conductance activated by the small oscillatory input current, and the relaxation time constant for this conductance. The ranges of the estimates for input capacitance and input resistance were comparable to the ranges of corresponding properties derived for neurons exhibiting "purely" passive behavior.(ABSTRACT TRUNCATED AT 400 WORDS)
Action Potentials↗
Active current electrodes for in vivo electrical impedance tomography.
The characterization of tissue by means of electrical impedance tomography requires accurate impedance measurements at relatively high frequencies. The present study describes the design and fabrication of broad-band, active, current electrodes for in vivo measurements. This approach eliminates the lead capacitances of the sourcing electrodes. The value of the resistors used were computed according to a protocol taking into account the constraints of a given application and the values and tolerances of the available components. Additional selection of the components further reduced the variability in circuit performance. The current sources designed according to the method described are usable at frequencies higher than 1 MHz, for differential load impedances up to 2000 omega. The parallel output conductance for each active electrode is 0.85 microS +/- 2%. The design method is valid for either adjacent or diametric drive, and can be applied to various applications by modifying the shape of the electrode.
Electric Conductivity↗
Rapid coating of glass-capillary microelectrodes for single-electrode voltage-clamp.
The single-electrode voltage-clamp technique requires sharp glass-capillary microelectrodes, whose electrical properties often limit the capabilities of the recording system. Here, we describe a rapid and simple way of coating fine microelectrodes with Dricote and Vaseline that improves their performance during voltage-clamp. The coating prevented clogging of the tips, improved the capacitance compensation of the electrodes, helped to seal the electrode tips into cell membranes and allowed visualization of the tips under saline solution. This new coating method led to greatly improved recordings and better characterization of the transduction and voltage-activated currents in an isolated preparation of spider mechanosensory neurons.
Animals↗
Urogenital re-education by electrostimulation: modelling for minimum energy computation.
The analysis of the voltage curve V(t) picked up between the two electrodes of a vaginal plug used with a current source stimulation allowed us to suggest a simple electrical model for intravaginal tissue. It is made up of three cells in series: a resistor in parallel with a capacitor for the first two, and a simple resistor for the third. Measurements throughout the hormonal cycle exhibit large variations in resistance and capacitance, and justify the use of a current source device to keep reproducible conditions of stimulation. Subjective detection of sensitivity threshold currents shows results which are independent of the day in the cycle and thus confirms the use of current source stimulation. The curve representing dissipated energy as a function of the pulse duration tau exhibits a minimum value different from the chronaxie (here 800 microseconds). The minimum value is effectively obtained at lower values of tau between 450 and 500 microseconds, dependent on the day of the cycle and the electrical characteristics of vaginal tissue. Two values of tau (230 and 1000 microseconds) between which the energy dissipated is less than Emin + 10 per cent are determined. This gap of pulse duration seems to be a correct range according to the minimum energy criterion for electrostimulation applied to urogenital re-education.
Electric Impedance↗
Electrical impedance monitoring of the wound-healing process.
The healing process was studied of five surgical wounds in sheep caused by the implantation of pacemaker electrodes in the vaginal or vulvar submucosa, while the electrodes were being used for impedometric measurements of the tissue surrounding them. Separate measurements of conductance (G) and capacitance (C) were carried out at frequencies ranging from 10 Hz to 100 kHz. The highest specific conductance at 100 kHz (mumho/cm) was observed on the 3rd postoperative day - 3095 +/- 172 SEM (n = 5), at which time the wound area was considerably swollen. Thereafter, the conductance gradually decreased and stabilized in 17-20 days at 2194 +/- 54 when the healing process was terminated. The decreasing impedance angle and tissue phase angle indicated that during the healing process cell volume decreased and cell density increased.
Animals↗
Modulation of pacemaker activity of sinoatrial node cells by electrical load imposed by an atrial cell model.
To investigate the electrotonic modulation of sinoatrial (SA) node pacemaker activity by atrial muscle, single or multiple (2-7) SA node cells isolated from rabbit hearts were connected to a membrane model [resistance-capacitance (R-C) circuit] of an atrial cell through an external circuit that mimics the gap junctional conductance (Gc) between cells. When Gc was 0 nS (uncoupled conditions), all the preparations generated regular and stable spontaneous action potentials with a mean cycle length (SCL) of 263 +/- 45 ms (+/- SD, n = 35). Step increases of Gc were associated with a progressive prolongation of SCL. At sufficiently high values of Gc, the spontaneous activity became irregular and finally stopped. We defined the threshold Gc causing an appreciable SCL irregularity as the minimum Gc at which the ratio of SD to mean of SCL was > 0.3. The threshold Gc for a single SA node cell was calculated to be 0.58 nS. In the presence of acetylcholine (ACh; 0.05-0.2 microM), the coupling-induced inhibition of spontaneous activity was greatly increased, and the threshold Gc for a single SA node cell was decreased in a concentration-dependent manner. These findings show that the pacemaker activity of SA node cells is easily inhibited when the cells are coupled to a passive atrial cell model and the inhibition is amplified by ACh. Computer simulation using a modified Oxsoft HEART model indicates that the passive atrial cell model acts as a current sink, imposing a substantial outward current on the SA node cell, and ACh amplifies the effect by activating an additional outward current.
Acetylcholine↗
Changes in passive electric parameters of human erythrocyte membrane during hyperthermia: role of spectrin phosphorylation.
In prefixed by 1 mmol/l OsO4 human erythrocytes, the discocyte shape was preserved upon heating to temperatures which include the denaturation temperature of the main peripheral protein spectrin. Nevertheless, the suspension of fixed cells displayed threshold decrease in its capacitance and resistance at the temperature range where spectrin denaturates. The same changes were established using intact cells and their resealed ghosts. For packed cells (ghosts), the capacitance and resistance decreased about 17% (31%) and 30% (19%). These data indicate a decrease in the beta dispersion of erythrocyte membrane associated, according to a previous study (Ivanov 1997), with the heat denaturation of spectrin at 49.5 degrees C. The amplitude of the 49.5 degrees C decrease in beta dispersion was reversibly reduced in intact erythrocytes and white ghosts following reversible decrease in the phosphorylation of their membrane proteins. It was fully eliminated in ghosts following their resealing with alkaline phosphatase (0.1 mg/ml) which dephosphorylated membrane proteins. These findings are discussed in relation to similar changes found in normal and tumour tissues and cells during hyperthermia.
Adenosine Triphosphate↗
Electrical stimulation of the auditory nerve: II. Effect of stimulus waveshape on single fibre response properties.
To investigate the generation of action potentials by electrical stimulation we studied the response of auditory nerve fibres (ANFs) to a variety of stimulus waveforms. Current pulses were presented to longitudinal bipolar scala tympani electrodes implanted in normal and deafened cochleae. Capacitively coupled monophasic current pulses evoked single ANF responses that were more sensitive to one phase (the 'excitatory' phase) than the other. Anodic pulses produced a significantly shorter mean latency compared with cathodic pulses, indicating that their site for spike initiation is located more centrally along the ANF. The fine temporal structure of ANF responses to biphasic pulses appeared similar to that evoked by monophasic pulses. An excitatory monophasic pulse evoked a significantly lower threshold than a biphasic current pulse having the same polarity and duration leading phase, i.e. the addition of a second phase leads to an increase in threshold. Increasing the temporal separation of the two phases of a biphasic pulse resulted in a moderate reduction in threshold which approached that of an excitatory monophasic pulse for interphase gaps > 100 micros. Greater threshold reductions were observed with narrower current pulses. There was a systematic reduction in threshold with increasing pulse width for biphasic current pulses, reflecting the general charge-dependent properties of ANFs for narrow pulse widths. Chopped biphasic current pulses, which uniformly delivered multiple packets of charge (2 x 30 micros, 3 x 20 micros or 6 x 10 micros) with the same polarity over a 120 micros period, followed by a similar series in the reverse polarity, demonstrated the ability of the neural membrane to integrate sub-threshold packets of charge to achieve depolarisation. Moreover, thresholds for these current pulses were approximately 1.5 dB lower than 60 micros/phase biphasic current pulses with no interphase gap. Finally, stimulation using charge-balanced triphasic and asymmetric current pulses produced systematic changes in threshold and latency consistent with the charge-dependent properties of ANFs. These findings provide insight into the mechanisms underlying the generation of action potentials using electrical stimuli. Moreover, a number of these novel stimuli may have potential clinical application.
Animals↗