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PubMed2004

Up-regulation of chondrocyte matrix genes and products by electric fields.

This study tested the hypothesis that selective and specific capacitively coupled electrical signals could stimulate gene expression and matrix production in bovine articular chondrocytes. Starting with a capacitively coupled electric signal that previously was shown to be effective in stimulating proliferation in bovine articular cartilage chondrocytes, dose responses were done sequentially for duration, response time, amplitude, duty cycle, and frequency. Results showed that a 0.5-hour, 20 mV/cm, signal at 60 kHz up-regulated aggrecan gene expression approximately eightfold (p < 0.0003) using a 50% duty cycle, whereas Type II collagen gene expression was up-regulated approximately fivefold (p < 0.02) using an 8.3% duty cycle. Using a compound signal (a 0.5-hour continuous period plus multiple 1-hour periods of 50% duty cycle for 7 days) both proteoglycan and collagen accumulation in vitro were increased approximately fivefold (p < 0.0003) and twofold (p < 0.0008), respectively. Also, the most effective capacitively coupled electric signal was different for each of the two molecules studied (aggrecan, 50% duty cycle and 4-hour response time; Type II collagen, 8.3% duty cycle and 6-hour response time). We conclude that selective up-regulation of gene expression and matrix accumulation of cartilage structural macromolecules (such as aggrecan and Type II collagen) with specific capacitively coupled fields occurs in vitro. This may be useful in vivo as a noninvasive modality to promote cartilage healing or ameliorate the effects of osteoarthritis, or both.

Aggrecans↗
PubMed2004

Hyperici herba extract interaction with artificial lipid bilayers.

Hyperici herba (Hyp) is the aerial part collected during the flowering period from the well-known herb, Hypericum perforatum. Black lipid membrane experiments were performed to investigate the effect of the ethanolic Hyp extract on the electrical properties (capacitance and conductance) of artificial lipid bilayers. Hyp extract (1-10 microg mL(-1)) induced a concentration-dependent increase of both specific transmembrane capacitance and conductance in phosphatidylcholine (PC) membranes. The effect on conductance was enhanced when the Hyp extract (3 microg mL(-1)) was present on both sides of the membrane (Gm=77.89 +/- 8.81 nS cm(-2), n=5) compared with single-sided application (Gm=36.48 +/- 2.41 nS cm(-2), n=5). In bilayers containing PC and phosphatidylserine (PS), PC:PS, the Hyp extract effect was greater than on pure PC bilayers, although the surface charge was not the determining factor of this enhanced activity. Adding cholesterol to the PC:PS mixture reverted the conductance increase induced by the Hyp extract in a dose-dependent manner. The specific pattern of the Hyp extract interaction with lipid bilayers has possible consequences concerning its absorption and bioavailability, as well as its pharmacodynamic effects on neuronal excitability.

Cell Membrane↗
PubMed1997

Electrical stimulation induces the level of TGF-beta1 mRNA in osteoblastic cells by a mechanism involving calcium/calmodulin pathway.

It is well-known that electrical stimulation can prompt healing of bone fractures. However, the mechanism involved is less clear. In this study, we found that capacitively coupled electric field-induced proliferation of osteoblastic cells (MC3T3-E1) accompanied increased levels of transforming growth factor-beta 1 (TGF-beta1) mRNA determined by quantitative reverse transcription/polymerase chain reaction. Previous reports have shown that verapamil and W-7, both of which block voltage gated calcium channels and inhibit the activation of cytosolic calmodulin, respectively, blocked capacitively coupled electric field-induced proliferation of the osteoblast cells. Interestingly, we found that verapamil and W-7 can also block capacitively coupled electric field-induced elevation of TGF-beta1 mRNA. This result suggested that electrical stimulation induces the level of TGF-beta1 mRNA in osteoblastic cells by a mechanism involving calcium/calmodulin pathway. The potential roles of TGF-beta in the electrical signal-induced osteogenesis was discussed.

3T3 Cells↗
PubMed1998

Reduction in excitability of the auditory nerve following acute electrical stimulation at high stimulus rates: III. Capacitive versus non-capacitive coupling of the stimulating electrodes.

Safe electrical stimulation of neural tissue is typically achieved using charge-balanced biphasic current pulses, which are designed to minimize the generation of direct current (DC) and the production of harmful electrochemical products. However, due to the kinetics of the charge injection process, neural stimulators must also use capacitive coupling or electrode shorting techniques, to ensure DC levels are minimal. Previous studies have reported a reduction in excitability of the auditory nerve following acute simulation at high rates and intensities. Elevated levels of DC were reported in these studies despite using charge-balanced biphasic pulses and electrode shorting. The present study was designed to investigate the extent to which DC contributed to these stimulus induced reductions in auditory nerve excitability. Adult guinea pigs were bilaterally implanted and unilaterally stimulated for two hours using charge-balanced biphasic current pulses and stimulus rates of 200, 400 or 1000 pulses/s (pps) at a stimulus intensity well above clinical levels (0.34 microC/phase). DC levels were controlled using either electrode shorting, or electrode shorting with capacitive coupling. Electrically evoked auditory brainstem responses (EABRs) were recorded before and periodically following the acute stimulation. It was found that the extent of reduction in the EABR amplitude was a function of stimulus rate. While there was little change in the EABR following stimulation at 200 pps, significant post-stimulus reductions in the EABR amplitude were observed at stimulus rates of 400 and 1000 pps during the three hour post-stimulus monitoring period. Stimulation using capacitively coupled electrodes, which eliminated all DCs, showed reductions in EABR amplitudes similar to those observed following stimulation using electrode shorting alone. While there was no significant difference in the extent of reduction in EABR amplitudes for capacitive coupling versus electrode shorting at stimulus rates of 200 pps (P > 0.05) and 400 pps (P > 0.05), there was a significant difference at 1000 pps (P< 0.001). The present findings indicate that the major component of the stimulus induced reductions observed in auditory nerve excitability appear to be associated with stimulus induced neuronal activity, although elevated levels of DC ( > 2.5 microA) can also contribute to these changes. However, although statistically significant, the effects of DC are very small compared to the effects of high rate, high intensity stimulation per se.

Animals↗
PubMed1993

Effect of electrical stimulation on lumbar paraspinal muscles.

Forty healthy, sedentary, premenopausal women were entered into a randomized, single-blind, controlled study to determine the effects of capacitively coupled electrical stimulation on the strength of the lumbar paraspinal muscles and the bone mineral in the lumbar spine. All were between 35 and 45 years of age and had normal physiologic estrogen. The study group received electrical stimulation over the lower lumbar paraspinal muscles for 30 minutes twice a day. Isometric strength of the lumbar paraspinal muscles was assessed with a strain-gauge dynamometer at entry and again after 3, 6, 9, and 12 months. Bone mineral was measured in the lumbar spine by dual-energy x-ray absorptiometry at entry and at 6 and 12 months. After 3 months, the median increase in isometric strength was 8.1% in the study group and 1.6% in the control group (P < 0.03). This initial difference was maintained during the remainder of the study. No further changes were seen between the two groups at 6, 9, and 12 months. It was concluded that capacitively coupled electrical muscle stimulation can, throughout a 1-year period, improve and maintain isometric strength of the lumbar paraspinal muscles independent of exercise, but it has no measurable effect on bone mass in the lumbar spine.

Absorptiometry, Photon↗
PubMed2003

Chick hair cells do not exhibit voltage-dependent somatic motility.

It is generally believed that mechanical amplification by cochlear hair cells is necessary to enhance the sensitivity and frequency selectivity of hearing. In the mammalian ear, the basis of cochlear amplification is believed to be the voltage-dependent electromotility of outer hair cells (OHCs). The avian basilar papilla contains tall and short hair cells, with the former being comparable to inner hair cells, and the latter comparable to OHCs, based on their innervation patterns. In this study, we sought evidence for somatic electromotility by direct measurements of voltage-dependent length changes in both tall and short hair cells at nanometre resolution. Microchamber and whole-cell voltage-clamp techniques were used. Motility was measured with a photodiode-based measurement system. Non-linear capacitance, an electrical signature of somatic motility, was also measured to complement motility measurement. Significantly, chick hair cells did not exhibit somatic motility nor express non-linear capacitance. The lack of somatic motility suggests that in avian hair cells the active process resides elsewhere, most likely in the hair cell stereocilia.

Animals↗
PubMed2002

Functional motor microdomains of the outer hair cell lateral membrane.

The outer hair cell (OHC) of the mammalian inner ear is a highly partitioned neuroepithelial cell whose lateral membrane is devoted to electromotility, a fast mechanical length change owing to the motor protein, prestin. Spatially restricted measures of prestin-derived nonlinear capacitance or gating charge, using either electrical amputation or discrete membrane mechanical deformation, were used to determine that functional variation exists within the extensive lateral membrane of the cell. This was evidenced by variation in the motor's operating voltage range and sensitivity among microdomains within the lateral membrane. That is, localized regions of the membrane evidenced Boltzmann distributions of motor charge whose midpoint voltage and slope differed from those obtained for the whole cell. These data highlight the functional independence of microdomains and imply that measured whole cell characteristics may differ from the microscopic characteristics of elementary motors.

Animals↗
PubMed1997

Effect of electrical stimulation on callus maturation during callus distraction in rabbits.

Callus distraction is currently the most widely used technique for limb lengthening. Prolonged treatment time is its main shortcoming. In this study, we tested the effectiveness of electrical stimulation during various stages of lengthening in order to decrease the treatment time. Seventy-five New Zealand white rabbits, about 2 kg in body weight, were divided into five groups. All groups received single level tibial lengthening of 1 cm by callotasis using a mini-lengthener. Group 1 rabbits did not receive electrical stimulation and could move freely in their cages. Group 2 rabbits (sham control), with electrodes on their left legs, were restrained on a wooden frame for 8 hours every day without electrical stimulation. Group 3 rabbits received capacitively coupled electrical stimulation, 60 kHz, 500 mV, on the left leg for 8 hours every day during the distraction period. Group 4 rabbits received electrical stimulation during the neutralization period. Group 5 rabbits received electrical stimulation during both the distraction and neutralization period. All rabbits were restrained during electrical stimulation. Weekly radiographs were taken to determine the time of appearance of at least three neocortices in the lengthening callus. At that time, the fixators were removed. The healing indexes (total time in fixator divided by length gained, days/cm) in the five groups of rabbits were compared. The range of motion of the ipsilateral knees and ankles and complications of treatment were recorded. The results showed that electrical stimulation applied during leg lengthening by callus distraction can significantly reduce the treatment time and the healing indexes, but the electrical stimulation may contribute to decreased motion in the ipsilateral knee and ankle joints.

Animals↗
PubMed2003

Electrochemical activation of electrodes for amperometric detection of nitric oxide.

An open question in the literature of nitric oxide detection was investigated: does electrochemical activation account for the enhanced properties of certain presumed chemically-modified electrodes? Uniform electrodes of graphite, iridium, palladium, platinum, and ruthenium were exposed to potential cycling and then tested for amperometric response to nitric oxide to identify principles that govern electrochemical activation of nitric oxide electrodes. These electrodes were compared to similar electrodes that were not cycled. Only cycled graphite and ruthenium showed significantly increased responses. Graphite demonstrated enhanced performance after exposure to cycling potentials at which oxygen, CO(2), and soluble carbonates form, suggesting that erosion of the electrode enhanced its response by increasing the surface area accessible to nitric oxide. This may explain the performance of carbon fibers cycled to the same potentials in solutions containing metalloporphyrins. The response of ruthenium was enhanced after cycling to less extreme potentials at which soluble species do not form and at which a metallic conductive oxide, RuO(2), could lay down a stable, adherent layer on the electrode surface. Cycled ruthenium also exhibited a much greater increase in capacitance after cycling, consistent with the formation of a conductive surface layer.

Electric Capacitance↗
PubMed2003

Detection of viable Salmonella typhimurium by impedance measurement of electrode capacitance and medium resistance.

Three-electrode electrochemical impedance technique was investigated for detection of Salmonella typhimurium by monitoring the growth of bacteria in selenite cystine (SC) broth supplemented with trimethylamine oxide hydrochloride (TMAO.HCl) and mannitol (M). The change in the system impedance during the growth of bacteria was studied using frequency spectral scanning. It was found that the impedance at low frequencies (<10 kHz) mainly came from the double-charged layer capacitance, reflecting the changes at the electrode interface and the adsorption on the electrode surface. While at high frequencies (>10 kHz), the system impedance mainly depended on the medium resistance. The adsorption of bacteria on the electrode surface was detected by measuring low frequency impedance, and verified with Faradic impedance spectroscopy. Enumeration of S. typhimurium using a low frequency (1 Hz) capacitance measurement and a high frequency (1 MHz) resistance measurement were compared. The detection times were determined for quantitative analysis based on the growth curves of bacteria referring to either the medium resistance or electrode capacitance. The regression equations for the detection times (t(d), h) and the initial cell number (N, cells.ml(-1)) were t(d)=-1.24logN+13.4 with R(2)=0.98 and t(d)=-1.40logN+14.46 with R(2)=0.97 for the medium resistance and electrode capacitance methods, respectively.

Cell Count↗
PubMed2002

Frequency- and time-domain FEM models of EMG: capacitive effects and aspects of dispersion.

Electromyography (EMG) simulations have traditionally been based on purely resistive models, in which capacitive effects are assumed to be negligible. Recent experimental studies suggest these assumptions may not be valid for muscle tissue. Furthermore, both muscle conductivity and permittivity are frequency-dependent (dispersive). In this paper, frequency-domain and time-domain finite-element models are used to examine the impact of capacitive effects and dispersion on the surface potential of a volume conductor. The results indicate that the effect of muscle capacitance and dispersion varies dramatically. Choosing low conductivity and high permittivity values in the range of experimentally reported data for muscle can cause displacement currents that are larger than conduction currents with corresponding reduction in surface potential of up to 50% at 100 Hz. Conductivity and permittivity values lying toward the middle of the reported range yield results which do not differ notably from purely resistive models. Also, excluding dispersion can also cause large error-up to 75% in the high frequency range of the EMG. It is clear that there is a need to establish accurate values of both conductivity and permittivity for human muscle tissue in vivo in order to quantify the influence of capacitance and dispersion on the EMG signal.

Computer Simulation↗
PubMed2006

A note on the local current associated with the rising phase of a propagating impulse in nonmyelinated nerve fibers.

To extend our recent paper dealing with the cable properties and the conduction velocity of nonmyelinated nerve fibers (Bull. Math. Biol. 64, 1069; 2002), the behavior of the local current associated with the rising phase of a propagating action potential is discussed. It is shown that the process of charging the membrane capacity by means of the local current plays a crucial role in determining the velocity of nerve conduction. The symmetry of the local current with respect to the boundary between the resting and active regions of the nerve fiber is emphasized. It is noted that there are several simple quantitative rules governing the intensities of the capacitive, resistive and total membrane currents observed during the rising phase of an action potential.

Action Potentials↗
PubMed2007

Measurements of membrane patch capacitance using a software-based lock-in system.

On-cell patch-clamp capacitance measurements can resolve the fusion of individual vesicles to a membrane patch and the accompanying dilation of the fusion pore. So far, these measurements have used a patch-clamp amplifier in combination with a hardware lock-in amplifier. Usually, solely the capacitance and conductance outputs of hardware lock-in amplifiers were recorded, which needed to be filtered rather heavily to suppress spectral components at the stimulus frequency. Therefore, the temporal resolution was limited, and information carried in the patch current was not utilized. In this paper, we describe an alternative and more versatile approach for measuring patch capacitance and conductance, using a digitally controlled patch-clamp amplifier. The software lock-in system showed better bandwidth and identical signal-to-noise performance needing less instrumentation. High temporal resolution measurements on patches of chromaffin cells showed that vesicle fission can be completed in only tens of microseconds. Capacitance calculation based on the patch current allows for straightforward offline phase correction. Moreover, the close inspection of direct current for the first time revealed small current changes accompanying the fusion and fission of large secretory vesicles, promising new insights into the vesicles' membrane properties. A practical guide to high-resolution on-cell patch-clamp capacitance measurements using the software lock-in is provided.

Algorithms↗
PubMed2005

Capacitance and conductance of single-walled carbon nanotubes in the presence of chemical vapors.

Simultaneous conductance and capacitance measurements on a single-walled carbon nanotube (SWNT) network are used to extract an intrinsic property of molecular adsorbates. Adsorbates from dilute chemical vapors produce a rapid response in both the capacitance and the conductance of the SWNT network. These responses are caused by a combination of two distinct physiochemical properties of the adsorbates: charge transfer and polarizability. We find that the ratio of the conductance response to the capacitance response is a concentration-independent intrinsic property of a chemical vapor that can assist in its identification.

Adsorption↗
PubMed2003

The strength-duration relationship of monophasic waveforms with varying capacitance sizes in external defibrillation.

The shape of the shock waveform influences defibrillation efficacy. However, the optimal combination between capacitance size and truncation/tilt which can determine monophasic waveform's shape, has not been determined for external defibrillation. The purpose of this study was to assess the effects of varying capacitance and tilt on external defibrillation using exponential monophasic waveforms. In a pig model of external defibrillation (n = 10, 30 +/- 6 kg), nine exponential monophasic waveforms combining three capacitance values (30 microF, 60 microF, and 120 microF) and three tilt values (55%, 75%, and 95%) were tested randomly. The energy and leading edge voltage at 50% defibrillation success (E50 and V50) were used to evaluate defibrillation efficacy. E50 and V50 were determined by the Bayesian technique. The lowest stored E50 for the 30microF, 60 microF, and 120 microF waveforms were 90 +/- 12 J (95% tilt), 106 +/- 45 J (55% tilt), and 107 +/- 52 J (75% tilt), respectively. The lowest V50 for the 30 microF, 60 microF, and 120 microF waveforms were 2,439 +/- 166 V (95% tilt), 1,849 +/- 375 V (55% tilt), and 1,301 +/- 322 V (75% tilt), respectively. The average current at external defibrillation threshold demonstrated a strength versus pulse duration relationship similar to that seen with pacing. Reducing capacitance has the same effect as truncating the waveform. The E50 is more sensitive to tilt values changes in larger capacitance waveforms. This study suggests that the optimal combination between capacitance and tilt may be 120 microF and 55%-75% for external defibrillation.

Animals↗
PubMed2004

Fundamental aspects of contactless conductivity detection for capillary electrophoresis. Part II: Signal-to-noise ratio and stray capacitance.

The signal-to-noise ratio of a contactless conductivity detector for capillary electrophoresis was examined for different cell arrangements and operating parameters. The best signal-to-noise ratios, and hence the best detection limits, are obtained for frequencies which give highest sensitivity. Comparative experiments for three different excitation voltages (20, 100, and 200 V(pp)) showed that the best signal-to-noise ratios were achieved for the highest excitation voltage of 200 V(pp). Low conductivity of the background electrolyte solution is mandatory to obtain lowest noise levels, and also the improvement on applying high excitation voltages was best for the electrolyte solution with lowest conductivity. The diameter of the electrodes was found to have only a negligible effect, so that a tight fitting of the electrodes to the external diameter of the capillary is not necessary. A cell without shielding between the two electrodes showed significant direct coupling (stray capacitance) and lower signal-to-noise ratios for all experimental conditions used. A serious distortion of the peak shapes was also observed for this cell arrangement.

Electric Capacitance↗
PubMed2002

Mitochondrial porin incorporation into black lipid membranes: ionic and gating contribution to the total current.

We present a new ac device useful for simultaneous measurements of ionic charge movement (conductance) and gating charge displacement (capacitance) in mitochondrial porin channels incorporated in two kinds of black lipid membranes (BLMs), made up of phosphatidylinositol (charged surface) and oxidized cholesterol (neutral surface). In particular, we investigated the conductance/capacitance variations during the process of porin incorporation (VDAC) at different porin concentrations. While conductance variations are present throughout the porin concentration range investigated, a threshold value seems to be necessary in order to detect a significant capacitance variation. A clear steady state in both conductance and capacitance is reached for the phosphatidylinositol bilayer, while for the oxidized cholesterol membranes, the steady state is reached only for the conductance. The dependence of capacitance characteristics on the membrane applied voltage V(m) is investigated before porin incorporation and at the ionic current steady state. The results obtained confirm that before porin incorporation, there is a small dependence on V(m)(2), while afterwards we find evidence of a dual exponential voltage dependence (a result similar to that found for conductance). Finally, we investigated the capacitance dependence on the radius of the hole separating the two compartments of the cell used in the measurements. In this study, performed only with oxidized cholesterol, the radius was varied from 200 to 1050 microm. We observed a significant variation in the specific capacitance in particular for smaller radii. The results were interpreted by a simple geometrical model taking into account the influence of the torus.

Animals↗
PubMed2006

Paired-pulse depression at photoreceptor synapses.

Synaptic depression produced by repetitive stimulation is likely to be particularly important in shaping responses of second-order retinal neurons at the tonically active photoreceptor synapse. We analyzed the time course and mechanisms of synaptic depression at rod and cone synapses using paired-pulse protocols involving two complementary measurements of exocytosis: (1) paired whole-cell recordings of the postsynaptic current (PSC) in second-order retinal neurons and (2) capacitance measurements of vesicular membrane fusion in rods and cones. PSCs in ON bipolar, OFF bipolar, and horizontal cells evoked by stimulation of either rods or cones recovered from paired-pulse depression (PPD) at rates similar to the recovery of exocytotic capacitance changes in rods and cones. Correlation between presynaptic and postsynaptic measures of recovery from PPD suggests that 80-90% of the depression at these synapses is presynaptic in origin. Consistent with a predominantly presynaptic mechanism, inhibiting desensitization of postsynaptic glutamate receptors had little effect on PPD. The depression of exocytotic capacitance changes exceeded depression of the presynaptic calcium current, suggesting that it is primarily caused by a depletion of synaptic vesicles. In support of this idea, limiting Ca2+ influx by using weaker depolarizing stimuli promoted faster recovery from PPD. Although cones exhibit much faster exocytotic kinetics than rods, exocytotic capacitance changes recovered from PPD at similar rates in both cell types. Thus, depression of release is not likely to contribute to differences in the kinetics of transmission from rods and cones.

Animals↗