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PubMed2005

Focused ion beam-nanomachined probes for improved electric force microscopy.

Nanomachining and beam-assisted Pt deposition by a focused ion beam (FIB) was used to modify AFM probes for improved electric force measurements. Si(3)N(4) cantilevers have been endowed with a nano-electrode at the tip apex to confine the electro-sensitive area at the very tip. This action results in both a marked decrease of the parasitic capacitive effect and in an improved electric force microscopy (EFM) contrast and resolution, with respect to usual, full metal-coated cantilevers. This fabrication approach is suited to the development of innovative electro-sensitive probes, useful in different scanning probe techniques.

Journal Article↗
PubMed2002

Antibody/antigen affinity behavior in liquid environment with electrical impedance analysis of quartz crystal microbalances.

Electrical impedance analysis has been used to study anti-human immunoglobulin G (anti-h IgG) adsorption and the subsequent human immunoglobulin G (hIgG) or rabbit immunoglobulin G (rIgG) affinity reaction in aqueous liquids on a polystyrene (PS)-modified quartz crystal microbalance (QCM) surface. Time-dependent adsorption data of both the frequency shift and the electrical equivalent parameters (motional resistance, shunt capacitance, quality factor, etc) are monitored. It was found that the motional resistance, R, increases while the resonance frequency, f, decreases during both the anti-h IgG immobilization and the subsequent affinity process. Decreasing f primarily arises from the increased mass loading. Increasing R indicates more power dissipation (increased losses) in the system. The change in motional resistance, delta R, in the affinity reaction is considerably larger than that in anti-h IgG immobilization adsorption process, although the resonant frequency shifts, delta f, are very close in these two processes. Specifically, for a saturated solution, the ratio of delta R/delta f is 9.45 x 10 (-3) Omega/Hz for anti-h IgG adsorption and 28.1 x 10 (-3) omega/Hz for anti-h IgG/hIgG binding respectively, indicating the increased power dissipation with the increasing binding molecules. The shunt capacitance changes little in the hIgG binding process ( approximately 0.01 pF).

Animals↗
PubMed1985

A model for signal transmission in an ear having hair cells with free-standing stereocilia. IV. Mechanoelectric transduction stage.

A model is described for mechanoelectric transduction in hair cells with free-standing stereocilia in the alligator lizard cochlea. The model relates the angular displacement of the stereocilia to the receptor potential in the absence of the hair cell's membrane capacitance whose effect is considered elsewhere (Leong and Weiss, 1985, in preparation). The model consists of two parts: a population of membrane ionic channels and an electric network that relates the channel conductance to the equivalent resistance of the hair cell. The membrane ionic channels tend to open when the stereociliary tuft is displaced toward the kinocilium (or basal body) and tend to close when the tuft is oppositely displaced. The fraction of channels that is open for a given tuft displacement is governed by Boltzmann statistics and the energies of open and closed configurations of the channels are separated by a single energy barrier whose height depends on the angular displacement of the stereociliary tuft. The resulting channel conductance is a hyperbolic-tangent type function of the angular displacement of the stereociliary tuft. The channel conductance is coupled to the rest of the hair cell by an equivalent electric network containing constant resistance and a capacitance. The Thévenin equivalent resistance change across the basolateral membrane of the hair cell, called the transducer function, is also a hyperbolic-tangent type function of angular displacement. The parameters of the channel conductance and the values of resistances in the hair-cell electric model determine the scale factors and the location of the operating point of this hyperbolic-tangent type function. The hyperbolic-tangent type function is a specific example of a class of monotonically decreasing and saturating, or sigmoidal, transducer functions. The spectral properties of sigmoidal transducer functions are examined for sinusoidal angular displacements of amplitude theta. General results are obtained for arbitrary sigmoidal transducer functions; particular results are obtained for the hyperbolic-tangent type function. General conclusions concerning spectral components of the resistance change include: all spectral components are independent of the frequency of the angular displacement; the constant or DC component can be positive or negative; the fundamental component is 180 degrees out of phase with the angular displacement, i.e. the resistance decreases when the stereocilia are displaced towards the kinocilium; for small values of theta, the magnitude of the nth harmonic tends to grow as theta n for n greater than 0; the zeroth harmonic or DC component grows as theta 2.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Essential helix interactions in the anion transporter domain of prestin revealed by evolutionary trace analysis.

Prestin, a member of the SLC26A family of anion transporters, is a polytopic membrane protein found in outer hair cells (OHCs) of the mammalian cochlea. Prestin is an essential component of the membrane-based motor that enhances electromotility of OHCs and contributes to frequency sensitivity and selectivity in mammalian hearing. Mammalian cells expressing prestin display a nonlinear capacitance (NLC), widely accepted as the electrical signature of electromotility. The associated charge movement requires intracellular anions reflecting the membership of prestin in the SLC26A family. We used the computational approach of evolutionary trace analysis to identify candidate functional (trace) residues in prestin for mutational studies. We created a panel of mutations at each trace residue and determined membrane expression and nonlinear capacitance associated with each mutant. We observe that several residue substitutions near the conserved sulfate transporter domain of prestin either greatly reduce or eliminate NLC, and the effect is dependent on the size of the substituted residue. These data suggest that packing of helices and interactions between residues surrounding the "sulfate transporter motif" is essential for normal prestin activity.

Amino Acid Sequence↗
PubMed1990

Role of corticosterone on the development of passive electrical properties of cultured chick embryo neurons.

We worked with neuronal cells of chick embryo cultures. The cells were obtained from 7 days-old embryos and cultured for 12 days. The experimental group was submitted to a single dose of corticosterone during the first 48 hours of culture. We measured the membrane resting potential at different external potassium concentrations, as well as the passive electrical properties of the membrane, resistance, time constant and capacitance. We found that the control cells develop progressively their potassium permeability and the electrical properties of the membrane until reaching values in this parameters that were similar to those found in adult cells. Corticosterone application induced a significant enhancement in these parameters in 3 and 6 days-old cultures as compared with the control cultures. These results suggest that glucocorticoids accelerate the differentiation process of the neurons in culture when applied at very early stages of development. We discuss the possible mechanisms involved in this action.

Animals↗
PubMed1995

Comparison of various bovine sperm capacitation systems for their ability to alter the net negative surface charge of spermatozoa.

Semen was divided into five aliquots and capacitated for 4 or 6 h in calcium-free Tyrode's (37 degrees C), modified Tyrode's bovine follicular fluid (39 degrees C), modified Tyrode's heparin (39 degrees C), and TEST-yolk buffer (4 degrees C) or incubated in BSA-saline (39 degrees C). Sperm before and after capacitation were electrophoresed at 100 V of constant current for 3 and 6 min. Samples were collected, sperm were counted, and percentages of sperm migrating toward the anode at 0 h and 4 or 6 h were calculated. At 0 h, 61 to 80% of the sperm migrated with a net negative charge. After 4 or 6 h, the percentage of sperm migrating toward the anode significantly decreased in all capacitation media but not in the control. The percentage of sperm migrating toward anode was lowest in calcium-free Tyrode's (22.1%) followed by TEST (28.4%), Tyrode's follicular fluid (29.5%), and Tyrode's heparin (42.5%); these values were less than those for the control (56.0%). The movement of live sperm without the influence of current or freeze-killed sperm under the influence of electrical current (control trials) was negligible. Capacitation reduced the net negative surface charge of sperm, the magnitude of which depended on capacitation system. Net negative charge of sperm was inversely associated with efficiency in penetration of zona-free hamster oocytes.

Animals↗
PubMed2006

Directional flow induced by synchronized longitudinal and zeta-potential controlling AC-electrical fields.

Electroosmotic flow (EOF) in a microchannel can be controlled by electronic control of the surface charge using an electrode embedded in the wall of the channel. By setting a voltage to the electrode, the zeta-potential at the wall can be changed locally. Thus, the electrode acts as a "gate" for liquid flow, in analogy with a gate in a field-effect transistor. In this paper we will show three aspects of a Field Effect Flow Control (FEFC) structure. We demonstrate the induction of directional flow by the synchronized switching of the gate potential with the channel axial potential. The advantage of this procedure is that potential gas formation by electrolysis at the electrodes that provide the axial electric field is suppressed at sufficiently large switching frequencies, while the direction and magnitude of the EOF can be maintained. Furthermore we will give an analysis of the time constants involved in the charging of the insulator, and thus the switching of the zeta potential, in order to predict the maximum operating frequency. For this purpose an equivalent electrical circuit is presented and analyzed. It is shown that in order to accurately describe the charging dynamics and pH dependency the traditionally used three capacitor model should be expanded with an element describing the buffer capacitance of the silica wall surface.

Buffers↗
PubMed1992

Education and engineering solutions for potential problems with laparoscopic monopolar electrosurgery.

The potential problems of monopolar electrosurgery relate to unrecognized energy transfer ("stray current") outside the view of the laparoscope. Mechanisms of stray current and unrecognized tissue injury include: (1) insulation breaks in electrodes; (2) capacitive coupling, or induced currents through the intact insulation of the active electrode to surrounding cannulas or other instruments; and (3) direct coupling (or unintended contact) between the active electrode and other metal instruments or cannulas within the abdomen. Capacitive coupling poses the greatest risk for injury when the outer conductor (trocar cannula or irrigation cannula) is electrically isolated from the abdominal wall by a plastic nonconductor. Capacitive coupling is increased by the coagulation mode (versus cut), open circuit (versus tissue contact with the electrode), 5-mm cannulas (versus 11 mm), and higher voltage generators. The safety of electrosurgery can be enhanced by surgical education regarding the biophysics of radio frequency electrical energy, technical choices in instruments using all-metal cannula systems, and engineering developments with a dynamically monitored system for insulation failure and capacitive coupling.

Electric Conductivity↗
PubMed1989

Aging and ethanol alter neuronal electric membrane properties.

The effect of age of donor mouse and acute ethanol exposure on the electrical membrane properties (EMP) of 825 freshly dissociated dorsal root ganglion (DRG) neurons was investigated. Both age and ethanol exerted a number of significant linear and independent effects. Age effects included a 52% increase in action potential overshoot, a 50% increase in a measure of afterhyperpolarization duration, a 31% increase in action potential duration due to decreased rate of repolarization and depolarization, and decreased electrical excitability. Also, specific membrane resistance increased and specific membrane capacitance decreased while the membrane time constant was not significantly affected by age. These EMP alterations with age for freshly dissociated DRG neurons are consistent with those reported previously for cultured DRG neurons and hence further support the hypothesis that the EMP of neurons in situ change significantly with age. Acute ethanol exposure caused relatively few EMP alterations including decreased electrical excitability, specific membrane capacitance, time constant, and overshoot; specific membrane resistance was increased. These changes are similar to those seen previously and are consistent with a membrane expansion effect of ethanol.

Action Potentials↗
PubMed1990

Capacitive coupling as an adjunctive treatment for avascular necrosis.

The purpose of this study was to determine the effectiveness of capacitive coupling, a noninvasive method for applying electrical stimulation to biologic tissues, when used as an adjunct to decompression and grafting in the treatment of avascular necrosis (AVN) of the femoral head. It also compared the results of core decompression and grafting with nonoperative management. Forty patients with Stages I-III AVN of the femoral head were treated with core decompression and grafting. All wore capacitive coupling units with electrodes placed over the femoral head continuously for six months. One-half of these units were active and one-half were inactive. Patients were followed for two to four years. Results were determined by preoperative and postoperative Harris ratings, quantitative roentgenographic measurements, and the number of hips that required total hip arthroplasty (THA). After all evaluations were completed, patients were divided into stimulated and nonstimulated groups. Patients in both groups were similar regarding gender, etiology, and roentgenographic stage of involvement. Results were also compared to 55 hips previously treated symptomatically, without surgery or electrical stimulation. There were no fractures, infections, or other significant complications in any of the hips operated on. Hips treated with decompression and grafting, both with and without electrical stimulation, were more satisfactory than hips treated symptomatically in regard to roentgenographic progression and the need for THA. There was, however, no indication that the addition of capacitive coupling gave better results than decompression and grafting alone.

Bone Transplantation↗
PubMed1972

Voltage-clamp analysis of the early current in frog skeletal muscle fibre using the double sucrose-gap method.

1. The early membrane currents in skeletal muscle fibres have been studied with the double sucrose-gap method, according to the experimental procedure used for the study of the giant axon of the squid.2. The earliest observable current is a capacitative transient. An equivalent circuit with two capacity-resistance systems can account for such a current. The components of the electrical circuit are estimated from the records.3. The capacitative transient current is followed by an initial current, the time and voltage dependence of which are analogous to those of nerve fibres. During this phase of current, the membrane behaves like a sodium electrode for modifications of the external sodium concentration.4. Using tetrodotoxin, a specific inhibitor of the sodium permeability, it is possible to separate two current components, (i) a transient component, suppressed by tetrodotoxin, which reflects the modifications, with time and voltage, of the membrane permeability towards sodium ions; the larger the depolarization, the shorter the time to reach peak current. This current is inward for depolarizations (V) of about +30 mV to about +130 mV (V(Na)). There was some variation in these values between individual fibres. Beyond V(Na), the current is outward. This current shows a small rectification - inward going - for high depolarizations which is comparable to the behaviour of the Ranvier node membrane. (ii) A quasi-instantaneous outward component, only voltage dependent. The current-voltage relation of this current shows an outward going rectification for high depolarizations. This current can be considered as a ;leak' current, in which chloride ions could play an important role.5. A sodium tail current is observed when the imposed potential fall occurs during the time course of the initial current. It corresponds to the deactivation of the sodium current previously activated. Because of the large contemporary capacitative currents, it is difficult to measure accurately its maximum amplitude and its time course: yet, the instantaneous current-voltage relation seems to show a slight rectification for the largest depolarizations, as observed on the Ranvier node membrane.6. The inactivation properties of the sodium current are studied in experiments similar to those described by Hodgkin & Huxley. As in nerve fibres the ability of the membrane to undergo an increase of the sodium permeability depends on the membrane potential. In our experimental conditions, the availability of the sodium carrying system is 90 per cent at the resting potential; the half-inactivation occurs for V = +11 mV. This potential value corresponds to the smallest value of tau(h) (-1), in agreement with the equations proposed by Hodgkin & Huxley (1952d) for the inactivation process.7. The activation parameters (m(infinity), tau(m)) are determined by a fitting method, taking account of the values of tau(h) previously established. The potential of half-activation is near V = +40 mV.

Action Potentials↗
PubMedDate not supplied

Electrical stimulation of spinal fusion: a scientific and clinical update.

BACKGROUND CONTEXT: For over two decades, a number of electrical stimulation devices have achieved increasing acceptance as adjuncts to lumbar spinal fusion. Direct current electrical stimulation, pulsed electromagnetic fields and more recently capacitive coupling have been shown to have varying effectiveness when used to increase the success of lumbar spinal fusion. PURPOSE: The various electrical stimulation devices will be reviewed with respect to the available basic science evidence validating their use as spinal fusion adjuncts, as well as a review of the current clinical data available to allow not only a discussion of their overall clinical applicability, but more specifically their use in specific spinal disorders and spinal fusion techniques. METHODS: The existing peer-reviewed scientific literature will be used to ascertain the scientific and clinical efficacy of electrical stimulation to enhance lumbar spinal fusion. CONCLUSION: Electrical stimulation devices have emerged as valid adjuncts to attaining a solid lumbar spinal fusion. However, not all stimulators are equally scientifically effective nor are they equally effective clinically in achieving increased fusion success.

Electric Stimulation Therapy↗
PubMed2005

Finite-element analysis of capacitive micromachined ultrasonic transducers.

In this paper, we present the results of finite-element analysis performed to investigate capacitive micromachined ultrasonic transducers (CMUTs). Both three-dimensional (3-D) and 2-D models were developed using a commercially available finite-element modeling (FEM) software. Depending on the dimensionality of the model, the membranes were constructed using plane or shell elements. The electrostatic gap was modeled using many parallel plate transducers. An axisymmetric model for a single membrane was built; the electrical input impedance of the device then was calculated in vacuum to investigate series and parallel resonant frequencies, where the input impedance has a minimum and a maximum, respectively. A method for decomposing the membrane capacitance into parasitic and active parts was demonstrated, and it was shown that the parallel resonant frequency shifted down with increased biased voltage. Calculations then were performed for immersion transducers. Acoustic wave propagation was simulated in the immersion medium, using appropriate elements in a 3-D model. Absorbing boundaries were implemented to avoid the reflections at the end of the medium mesh. One row of an array element, modeled with appropriate boundary conditions, was used to calculate the output pressure. The results were compared with a simpler model: a single membrane in immersion, with symmetry boundary conditions on the sidewalls that cause the calculations to reflect the properties of an infinitely large array. A 2-D model then was developed to demonstrate the effect of membrane dimensions on the output pressure and bandwidth. Our calculations revealed that the small signal transmit pressure was inversely proportional to the square root of gap height. We also compared FEM results with analytical and experimental results.

Computer Simulation↗
PubMed2005

Prestin-dependent and prestin-independent motility of guinea pig outer hair cells.

The motile response of isolated guinea pig outer hair cells (OHCs) was investigated using a combination of whole-cell patch clamp recording and continuous video image analysis. OHC's length, width, and area were measured from video images and the cell volume estimated from these values. Morphological data was then correlated with electrophysiological recordings of whole-cell current, membrane potential and voltage-dependent non-linear capacitance. Electromotility was evoked either by manipulating the membrane potential under voltage-clamp conditions or by exposing OHCs to high K+ solutions. Other motile responses were investigated in voltage-clamp experiments at constant holding potential, or exposing OHCs to solutions that did not affect the membrane potential. We found that electrical stimulation evoked voltage-dependent changes in OHC's length, width and area but not in cell volume regardless of the time course of stimulation. Moreover, changes in cell area were always associated with both voltage-dependent motility and non-linear capacitance, suggesting prestin dependency. In contrast, voltage-independent motile responses at constant membrane potential, which are presumed to be prestin-independent, were associated with changes in cell length, width and volume without significant changes in area. Area measurements, then, become a tool to investigate the simultaneous occurrence of both prestin-dependent and prestin-independent OHC motilities, and for evaluating the individual contribution of each mechanism to the total cell movement.

Animals↗
PubMed1989

Phase tracking: an improved phase detection technique for cell membrane capacitance measurements.

We describe here a technique called phase tracking that greatly improves the accuracy of measurements of the membrane capacitance of single cells. We have modified the original phase detection technique to include a method for creating calibrated changes in the resistance in series with the cell. This provides a method to automate the adjustment of the phase detector to the appropriate phase angle for measuring membrane capacitance. The phase determination depends only on the cell's electrical parameters and does not require matching of the cell impedance with that of the slow capacitance cancellation circuitry of the patch-clamp amplifier. We show here that phase tracking can accurately locate the phase of the capacitance signal and can keep the detector aligned with this signal during measurements of exocytosis in mast cells, irrespective of the large drifts which occur in cell membrane resistance, membrane capacitance, or series resistance. The phase tracking technique is a valuable tool for quantifying exocytosis and endocytosis in single cells.

Animals↗
PubMed1990

Electrical properties of metallic electrodes.

The series equivalent resistance R and capacitance C of metal/saline electrode/electrolyte interfaces were measured as a function of frequency (100 Hz-20k Hz) and current density (0.25 to 1000 A m-2) for eight typical electrode metals. For each of the metals tested, R decreased and C increased as the current density was increased above a critical value (with the exception of silver and MP35N at frequencies above 1 kHz for which R increased and C decreased slightly). With the exception of copper, the current density linearity limit (for 10 per cent decrease in R or 10 per cent increase in C) increased with increasing frequency and, in most cases, the current density linearity limit for 10 per cent increase in C was slightly less than that for 10 per cent decrease in R. Among the metals tested, copper and aluminium had the lowest current carrying capability and rhodium had the highest current-carrying capability. The current carrying capabilities of 316 SS, platinum, silver and MP35N, were intermediate and similar. With increasing current density, an increase in the electrode/electrolyte capacitance was the most sensitive indicator of the current-carrying linearity limit.

Electric Conductivity↗
PubMed2001

Surface of human sperm bears three differently charged CD52 forms, two of which remain stably bound to sperm after capacitation.

gp20 is a sialoglycoprotein of the human sperm surface with a core peptide homologous to the leukocyte antigen CD52, a GPI-anchored glycosylated protein which is described by the monoclonal antibody CAMPATH-1. Comparative analyses, by means of CAMPATH and anti-gp20, indicated that they describe it in morphologically and functionally different ways, suggesting that the respective epitopes are different but also casting doubt on the immunological identity of the antigen. In the present study, we used immunodepletion to demonstrate that CAMPATH and anti-gp20 interact with the same antigen, but that anti-gp20 has a much higher avidity for the antigen than CAMPATH. Anion exchange fractionation analysis of the antigen revealed three differently charged gp20-CD52 forms, the least charged of which, was largely without a GPI-anchor. All three forms were associated with freshly ejaculated sperm, whereas capacitated sperm only contained the two GPI-anchored, more charged forms, which were also the ones found in the prostasome fraction of seminal plasma and in leukocytes. The two charged, GPI-anchored forms were described as homogeneous by anti-gp20, since they ran as a singlet; the third form ran as a doublet. When tested for insertion into Jurkat T cells, the medium charged form inserted the most readily and the less charged one could not be inserted at all.

Antibody Specificity↗
PubMed1990

Improved technique for testing autonomic dysfunction: evaluation of transient behaviour of the autonomic response.

The transient behaviour of the autonomic response has been studied by means of a reactometer incorporating self-balancing of the electrodermal impedance. This instrument has been used for the indirect measurement of certain parameters associated with the autonomic response detected as skin electrical resistance relative variation (SERV) and capacitance (SECV). Transient signals of the electrodermal impedance response were obtained online by differentiating the analogue output of the impedance reactometer: d(SERV)/dt and d(SECV)/dt. We describe here how the use of the transient signals of the electrodermal impedance response can improve the accuracy and reduce variability and dispersion of the results and how autonomic conduction velocities (ACV) can be indirectly measured.

Autonomic Nervous System↗