[The quantitative characteristics of the changes in the vascular capacitance of the basin of the anterior vena cava in cats under neurohumoral pressor actions].
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Animals↗
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[Current-voltage characteristics of bilayer lipid membranes formed on the substrates].
Current-voltage characteristics (CVC) of bilayer lipid membranes formed on the support (s-BLM) were measured in static mode as well as in cyclic one with the period 33 s. The new cut of the wire from stainless stell SS-10T served as the support. In the range of voltages -0.9-(+)0.9V the similarity of the CVC for s-BLM as well as for support- electrolyte border was observed. Static CVC for both objects satisfy the Tafel's equation with close parameters. If the voltage amplitudes were over 0.3 V, s-BLM specific capacitance approached the same value for the support-electrolyte border. Possible electrical models of s-BLM are discussed.
Lipid Bilayers↗
Validation of formamide as a detubulation agent in isolated rat cardiac cells.
Kawai M, Hussain M, and Orchard CH. Am J Heart Circ Physiol 277: H603-H609, 1999 developed a technique to detubulate rat ventricular myocytes using formamide and showed that detubulation results in a decrease in cell capacitance, Ca(2+) current density, and Ca(2+) transient amplitude. We have investigated the mechanism of this detubulation and possible direct effects of formamide. Staining ventricular cells with di-8-ANEPPS showed that the t tubule membranes remain inside the cell after detubulation; trapping of FITC-labeled dextran within the t tubules showed that detubulation occurs during formamide washout and that the t tubules appear to reseal within the cell. Detubulation had no effect on the microtubule network but resulted in loss of synchronous Ca(2+) release on electrical stimulation. In contrast, formamide treatment of atrial cells did not significantly change cell capacitance, Ca(2+) current amplitude, action potential configuration, the Ca(2+) transient or the response of the Ca(2+) transient to isoprenaline. We conclude that formamide washout induces detubulation of single rat ventricular myocytes, leaving the t tubules within the cell, but without direct effects on cell proteins that might alter cell function.
Action Potentials↗
Pneumatic-to-electrical analog for high-frequency jet ventilation of disrupted airways.
A pneumatic-to-electrical circuit analog is used to describe 2 separate mechanisms by which high-frequency jet ventilators sustain ventilation and oxygenation in the presence of large airway disruptions. The frequency-dependent mechanism is based on variations in the pneumatic equivalent to capacitive reactance. The pressure-dependent mechanism models lung defects on a voltage-controlled resistor. The electrical circuit model is also used to explain the factors leading to gas trapping and inadvertent positive end-expiratory pressure during high-frequency jet ventilation.
Airway Resistance↗
Cable properties of spinal cord motoneurons in adult and aged cats.
1. The electrophysiological properties of spinal cord alpha-motoneurons were investigated in adult cats (1-3 yr old) and old cats (14-15 yr old) using intracellular recording techniques. Voltage transients following depolarizing pulses of current were analyzed according to the procedure described by Ito and Oshima (15). The input resistance of each cell, together with the passive electrical time constants, were used to estimate the electrotonic length and total cell capacitance of each motoneuron. 2. Adult and old motoneurons both exhibited an undershoot of the membrane potential following the cessation of a subthreshold depolarizing current pulse (15). The average time constant for the decay of this undershoot in membrane potential was statistically indistinguishable in motoneurons of adult and aged animals. 3. The average membrane time constant of motoneurons in aged cats was 19% longer than that of motoneurons in adult cats. 4. The average total cell capacitance of motoneurons in aged cats was 16% smaller than that of motoneurons in adult cats. 5. The average electrotonic length of old motoneurons was statistically indistinguishable from that of motoneurons in adult cats. 6. From these results, we conclude that there is an age-dependent increase in the membrane resistance and an age-dependent decrease in cell surface area of alpha-motoneurons of the lumbar spinal cord in aged cats. Both of these phenomena are believed to contribute to the age-dependent increase in input resistance that has been previously reported to occur in motoneurons in aged cats (18).
Aging↗
Low-frequency dielectric spectroscopy as a tool for studying the compatibility between pharmaceutical gels and mucous tissue.
This interdisciplinary work demonstrates how low-frequency dielectric spectroscopy, a technique that is frequently used within physics, can be used to assess the possibilities of intimate surface contact between a polymer gel and mucous tissue, which is generally considered to be the first step in the mucoadhesion process. The dielectric responses of five different gels, of freshly excised porcine nasal mucosa and of systems made by combining the two were measured. All spectra were modeled by a Randles electric circuit containing a diffusion element, a barrier resistance in parallel with a capacitance, and a high-frequency resistance. The results were used to create a measure of the compatibility between the gel and the mucus, which we have named the compatibility factor. Thus, the compatibility factor provides us with a measure of the ease with which a charged species passes the interface between a gel and the mucus layer. The compatibility factor is calculated from the high frequency (kHz region) response of the gel, of the mucosa, and of the combined system. The two highest compatibility factors in this study were obtained for gels based on crosslinked poly(acrylic acid) and chitosan, which was in agreement with the results from mucoadhesion measurements that were performed using a tensile strength method.
Adjuvants, Pharmaceutic↗
Time courses of cell electroporation as revealed by submicrosecond imaging of transmembrane potential.
Changes in the membrane conductance of sea urchin eggs, during the course of electroporation, were investigated over the time range of 0.5 microsecond to 1 ms by imaging the transmembrane potential at a submicrosecond resolution with the voltage-sensitive fluorescent dye RH292. When a rectangular electric pulse of moderate intensity was applied across an egg, a position-dependent potential developed synchronously with the pulse, as theory predicts for a cell with an insulating membrane. From the rise and fall times, the membrane capacitance of unfertilized eggs was estimated to be 0.95 microF/cm2 and the intracellular conductance 220 omega.cm. Under an electric pulse of much higher intensity, the rise of the induced potential stopped at a certain level and then slowly decreased on the microsecond time scale. This saturation and subsequent reversal of the potential development was ascribed to the introduction of finite membrane conductance, or permeabilization of the membrane, by the action of the intense pulse (electroporation). Detailed analysis indicated the following: already at 0.5 microsecond in the rectangular electric pulse, the two sides of the egg facing the positive and negative electrodes were porated and gave a high membrane conductance in the order of 1 S/cm2; the conductance on the positive side appeared higher. Thereafter, the conductance increased steadily, reaching the order of 10 S/cm2 by 1 ms. This increase was faster on the negative-electrode side; by 1 ms the conductance on the negative side was more than twice that on the positive side. The recovery of the porated membrane after the pulse treatment was assessed from the membrane conductance estimated in a second electric pulse of a small amplitude. At least two recovery processes were distinguished, one with a time constant of 7 microseconds and the other 0.5 ms, at the end of which the membrane conductance was already < 0.1 S/cm2.
Animals↗
[Electrically induced osteogenesis. II. Experimental studies].
The paper presents the possibilities to induce osteogenesis using different types of electrical current. The direct current may be used with invasive or semi-invasive methods. Electrodes are placed internally, near the bone. Experiments showed that the optimum stimulation is achieved with current between 5 and 20 microamperes. The capacitive current is able to induce osteogenesis. The electrodes are placed externally; between the electrodes there is an electric field with the value ranged 1-10 millivolts/cm. The method of pulsed electromagnetic fields is based on the field produced by a coil placed externally. The magnetic field range between 0, 1 and 20 gauss. This is the most appreciate method because is noninvasive and offered the best experimental results.
Animals↗
Continuous recordings of impedance and phase angle during electrodermal reactions and the locus of impedance change.
The relatively few studies that use alternating current (AC) in exosomatic electrodermal recording techniques focus on tonic measurement but not on phasic measures. AC methods of phasic measurement, however, are most useful in testing electrical models of the electrodermal response. Problems arising from AC recording of fast electrodermal changes are discussed, and an appropriate measurement concept for continuous recording of impedance and phase angle is developed. This enables tonic values of both parameters to be offset in order to sufficiently amplify small changes. An AC frequency of 100 Hz was used in recording electrodermal activity in 10 subjects during an habituation series of 80dB 1000 Hz tones. Comparison of transformed curves showed that the main component of electrical changes accompanying electrodermal response is a shift in conductance while susceptance shows only small fluctuations. According to a widely accepted simple electrical model of skin, these results indicate that electrodermal responses take place mainly in the resistive element which parallels the capacitance associated with the stratum corneum, but that other components may be involved too.
Adult↗
Chemical detection with a single-walled carbon nanotube capacitor.
We show that the capacitance of single-walled carbon nanotubes (SWNTs) is highly sensitive to a broad class of chemical vapors and that this transduction mechanism can form the basis for a fast, low-power sorption-based chemical sensor. In the presence of a dilute chemical vapor, molecular adsorbates are polarized by the fringing electric fields radiating from the surface of a SWNT electrode, which causes an increase in its capacitance. We use this effect to construct a high-performance chemical sensor by thinly coating the SWNTs with chemoselective materials that provide a large, class-specific gain to the capacitance response. Such SWNT chemicapacitors are fast, highly sensitive, and completely reversible.
Journal Article↗
Electrical impedance and erythrocyte sedimentation rate (ESR) of blood.
The electrical impedance of blood is primarily determined by plasma resistance Rp, cell interior resistance Ri, and cell membrane capacitance Cm. These impedance parameters were measured for 62 samples with various erythrocyte sedimentation rates (ESR = 1-150 mm/h). A formula for estimating ESR by Rp and Cm was obtained by linear regression as: In (ESR) = 10.16-0.016 x f0, (r = 0.974, P < 0.001), where f0 = 10(9)/(2 pi.Rp100.Cm100) defined as the effective characteristic frequency in kHz, Rp100 = Rp/h in omega cm, Cm100 = Cm/h in pF/cm, h is the haematocrit in decimal. The 95% confidence intervals for the coefficients in the above equation were 9.73 to 10.59 and -0.017 to -0.015. The origin of the association was found reasonable since factors increasing the ESR, i.e., the concentration of some plasma proteins and the size of the blood cells, also elevate the capacitance. The results imply that the impedance measurement might be an alternative method for fast determination of the ESR.
Blood Sedimentation↗
Developmental changes in electrophysiological properties and synaptic transmission in rat intracardiac ganglion neurons.
We charted postnatal changes in the intrinsic electrophysiological properties and synaptic responses of rat intrinsic cardiac ganglion (ICG) neurons. We developed a whole-mount ganglion preparation of the excised right atrial ganglion plexus. Using intracellular recordings and nerve stimulation we tested the hypothesis that substantial transformations in the intrinsic electrical characteristics and synaptic transmission accompany postnatal development. Membrane potential (E(m)) did not change but time constant (tau) and cell capacitance increased with postnatal development. Accordingly, input resistance (R(in)) decreased but specific membrane resistance (R(m)) increased postnatally. Comparison of the somatic active membrane properties revealed significant changes in electrical phenotype. All neonatal neurons had somatic action potentials (APs) with small overshoots and small afterhyperpolarizations (AHPs). Adult neurons had somatic APs with large overshoots and large AHP amplitudes. The range of AHP duration was larger in adults than in neonates. The AP characteristics of juvenile neurons resembled those of adults, with the exception of AHP duration, which fell midway between neonate and adult values. Phasic, multiply adapting, and tonic evoked discharge activities were recorded from ICG neurons. Most neurons displayed phasic discharge at each developmental stage. All neurons received excitatory synaptic inputs from the vagus or interganglionic nerve trunk(s), the strength of which did not change significantly with postnatal age. The changes in the electrophysiological properties of the postganglionic neuron suggest that increased complexity of parasympathetic regulation of cardiac function accompanies postnatal development.
Action Potentials↗
Simulations of passive properties and action potential conduction in an idealized bullfrog atrial trabeculum.
This study investigates the properties of a distributed parameter model of an idealized trabeculum of cardiac muscle surrounded by a resistive-capacitive trabecular sheath. A mathematical approach is developed that permits the direct solution for the absolute potential in each medium [i.e., the intracellular (Vi), interstitial (Ve), and external (Vo) potentials), as opposed to obtaining solutions for the transmembrane potential V (where V identical to Vi-Ve). The mathematical description of the underlying individual cell is based upon quantitative whole-cell voltage-clamp measurements in bullfrog atrial myocytes. "Reduced" or "simplified" cell membrane models that lack the complete complement of transmembrane currents are compared with regard to their accuracy in representing the root, upstroke, and plateau regions of the propagated action potential in the complete model. The results show that a reduced cell membrane model must contain the sodium current INa, calcium current ICa, and background-rectifying K+ current IK1. A cell membrane model that contains a linear background K+ current IL instead of IK1 results in much poorer approximation to the upstroke, plateau, and conduction velocities of an action potential. The effects of varying the resistive-capacitive parameters of the trabecular sheath on both the passive properties (the time and space constants and the input resistance) and conduction parameters (time and space constants of the foot and conduction velocity of the action potential) of the trabeculum are also investigated. These simulations show that electrical activity within the trabeculum is much more sensitive to variations in the resistive component than in the capacitive component of the sheath. The trabecular sheath reduces the extracellular resistance seen by the cell by shunting current away from highly resistive interstitial medium into the volume conductor medium, which is of low resistance, and thereby increases conduction velocity. Finally, the addition of the cholinergic neurotransmitter acetylcholine to the extracellular medium reduces both the space constant of the trabeculum and the conduction velocity of propagated electrical activity.
Action Potentials↗
Improved defibrillator waveform safety factor with biphasic waveforms.
Excitation thresholds and arrhythmias were studied in "adult-type" cultured chick embryo myocardial cells after electric field stimulation with biphasic, truncated, and rectified underdamped RLC (resistance-inductance-capacitance) type waveforms, to test the hypothesis that the negative phase of biphasic waveforms ameliorates membrane dysfunction induced by the initial positive portion. Photocell mechanograms and intracellular microelectrodes monitored extrasystoles and depolarization-induced arrhythmias. Rectifying or truncating biphasic waveforms did not alter the excitation threshold. However, shock intensities producing specific postshock arrhythmias or a specific severity of postshock prolonged depolarization differed significantly when biphasic waveforms were truncated or rectified. The voltage gradient producing a specific dysfunction was 12-14% lower for the truncated version than for the biphasic; that for the rectified version was 17-27% lower than for the biphasic version (although both contained the same energy). Safety factor, the ratio between shock intensity producing specific dysfunction and that producing excitation, was determined for each waveform. Biphasic waveforms had larger safety factors than truncated or rectified waveforms. Since safety factor, as measured in cultured myocardial cells, closely corresponds with in situ defibrillating effectiveness (14), the significantly higher safety factors of biphasic waveforms suggest that carefully shaped biphasic waveforms might improve the efficacy and safety of cardiac defibrillation procedures.
Animals↗
Effects of glycerol treatment and maintained depolarization on charge movement in skeletal muscle.
1. Voltage-clamp experiments were carried out using the techniques described in the preceding paper. 2. In one series of experiments an attempt was made to disrupt the T-system with glycerol treatment. Muscles were soaked in Ringer + 400 mM glycerol for 1 hr at room temperature, transferred to Ringer + 5 mM calcium + 5 mM magnesium for 20-30 min, and then cooled to around 2 degrees C and placed in an isosmotic test solution containing tetrodotoxin for electrical measurements. 3. The density of charge seen in isosmotic tetraethylammonium (TEA) solution with strong depolarization, normalized according to fibre capacitance, was decreased by glycerol treatment to about one third the amount seen in untreated hypertonic fibres. 4. An analysis of fibre capacitance revealed that only 0-4 of the tubular capacitance was removed by this particular glycerol procedure. If the density of charge with respect to capacitance is corrected for this decrease in capacitance, the results indicate that glycerol treatment removed or immobilized 0-77 of the charge initially present. Thus the effect of glycerol treatment to reduce charge does not depend entirely on disrupting the electrical continuity of the T-system. 5. The effects of maintained depolarization were studied using a TEA Ringer made hypertonic with sucrose. When the voltage was changed from -80 to -21 mV the measurable charge movement declined exponentially to zero with a time constant of 13-24 sec. On repolarization the process recovered exponentially to the initial level with a time constant of 21-53 sec. 6. Experiments were also carried out using a sodium Ringer made hypertonic with sucrose. For small depolarizations only charge movement currents were seen, whereas for large depolarizations large delayed ionic currents, presumably carried by potassium, were observed. With moderate depolarizations in the range V = -40 to -30 mV, both components were of comparable magnitude. 7. A plot of the fractional charge movement (Q/Qmax) vs. V fitted at moderate depolarizations is similar to that of n infinity vs. V fitted at larger depolarizations. Values of n infinity were obtained by fitting the delayed ionic current to n4(V - VK). For voltages between -40 and -30 mV the time constant for charge tauQ was always less than taun; values of taun/tauQ varied from 1-6 to 4-3. 8. Glycerol treatment had little if any effect on the kinetics of delayed rectifier currents. Values of gK measured in isosmotic solution following glycerol were about one third the values obtained in untreated fibres in a hypertonic solution (osmolality three times normal). The threefold difference in gK is probably due to a similar difference in internal potassium concentration. 9. These results and others are difficult to reconcile with the idea that the charge movement process acts as a gate for potassium channels. It seems more likely that charge movement is a step in the activation of contraction.
Animals↗
The clinical use of bone stimulators.
Delay or failure of healing in long bone fracture is a common clinical problem confronting the orthopaedic surgeon, and can have significant impact on the quality of life for patients who have it. One treatment option for this problem is the use of electrical or ultrasonic bone stimulation. Electrical signals can be delivered with an implantable direct current stimulator, or noninvasively using inductive or capacitive coupling to induce currents in the tissues. Low-intensity ultrasound can speed the healing of fresh fractures. Although regarded with skepticism by many physicians, there is abundant evidence from clinical studies of the effectiveness of these treatments. In addition to dozens of retrospective reports, randomized, prospective, double-blind controlled trials have shown the efficacy of electrical stimulation for nonunion and ultrasound for speeding healing. Patients with unacceptable deformity, synovial pseudarthrosis, or large gaps are generally not good candidates for this treatment modality. This article is a review of the clinical literature regarding treatment of long bone nonunion with bone stimulators.
Electric Stimulation Therapy↗
Electrical properties of the myotendon region of frog twitch muscle fibers measured in the frequency domain.
The electrical properties of the end of a muscle fiber were determined using three microelectrodes, one passing sinusoidal current, the other two recording the resulting voltages. An electrical model was constructed from the morphology of the fiber, including the resistance of the extracellular space between cells; the parameters of this model were determined by fitting the model to the observed voltage responses. Our results, analyzed directly or by curve fits, show that the end of muscle fibers contains a large capacitance resulting from the extensive membrane folds at the myotendon junction. Analysis and simulations show that the extra capacitance at the myotendon junction has substantial effects on measurements of linear properties, in particular on estimates of the capacitance of the membranes. There is little qualitative effect on classical measurements of nonlinear charge movement (provided they were made with one set of electrode locations) if the linear components have been subtracted. Quantitative estimates of nonlinear charge movement and ionic currents are significantly affected, however, because these estimates are customarily normalized with respect to the linear capacitance.
Animals↗
Impedance analysis for the determination of epithelial and subepithelial resistance in intestinal tissues.
The barrier function of the intestinal wall plays a key role in body homeostasis and defense against noxious agents. Conventional Ussing chamber techniques determine the overall transmural resistance but do not differentiate epithelial and subepithelial tissues. The barrier function, however, resides in the epithelial cell layer only. Transmural impedance analysis can solve this problem, if adequate models are applied. We show that: (i) epithelial and subepithelial impedances are additive, (ii) the epithelium proper can be represented by a very general electrical model, which demonstrates short-circuiting at high frequencies (due to cell membrane capacitances), and (iii) the reactance of subepithelial tissue can be described phenomenologically. Using an empirical expression for description of the subepithelial impedance, the present method allows the determination of the epithelial and the subepithelial resistance. This was exemplified in rat ileum, which defied adequate impedance analysis so far. Of the transmural DC resistance of 61 +/- 5 omega.cm2 (n = 8) the subepithelial contribution was 28 +/- 2 omega.cm2 and the epithelial resistance was 33 +/- 4 omega.cm2.
Animals↗