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PubMed1993

Changes in recording electrode impedance during anaesthesia have no effect on evoked electromyographic responses.

Changes in electrical impedance at the recording electrodes have been blamed for the failure of evoked electromyographic responses to return to baseline during the offset of neuromuscular block, but a relationship between electrode impedance and electromyographic responses has never been shown. In 50 fit adults, the resistive and capacitive (reactive) components of the impedance of the recording electrodes were measured during electromyographic monitoring of neuromuscular transmission under enflurane anaesthesia. In 25 patients six 1 mm-deep punctures were made in the skin under both active recording electrodes, and in the other 25 no puncture was made. Electrode impedance was measured using an impedance bridge at a current density less than 60 microA cm-2. Skin puncture made no difference either to the electrode impedance, or to the decrement from the baseline of the first electromyographic response to the train-of-four stimuli after offset of neuromuscular blockade. The electrode impedance decreased in 48 of the patients, and increased slightly in the other two patients. There was no relationship between the decrease in the T1 response from baseline and the change in electrode impedance during electromyographic monitoring.

Adult↗
PubMed2001

Chlorpromazine alters outer hair cell electromotility.

OBJECTIVE: Outer hair cells (OHCs) of the inner ear rapidly convert electrical gradients into mechanical force, enhancing cochlear sensitivity and frequency selectivity. We investigated the effect of chlorpromazine, an antipsychotic medication that alters membrane biomechanics, on OHC electromotility. STUDY DESIGN: Isolated guinea pig outer hair cells were perfused with chlorpromazine under whole-cell patch-pipette recording conditions. Electromotile responses were measured. RESULTS: A dramatic, reversible, dose-dependent depolarization of voltage at peak capacitance (V(pkCm)) was seen with chlorpromazine treatment. The gain of the electromotile response was maximal near V(pkCm) both before and after chlorpromazine application. Unlike the 3 other agents that alter electromotility (salicylate, lanthanides, membrane tension), chlorpromazine did not change peak capacitance (Cm(pk)), which varies directly with maximal electromotile gain. CONCLUSION: Chlorpromazine changes the membrane voltage at which OHCs exhibit maximal electromotile gain, without changing the magnitude of electromotile responses. SIGNIFICANCE: Chlorpromazine may diminish hearing thresholds or otoacoustic emissions in large doses.

Animals↗
PubMed1990

Reflex control of vascular capacitance during hypoxia, hypercapnia, or hypoxic hypercapnia.

We tested the hypothesis that the changes in venous tone induced by changes in arterial blood oxygen or carbon dioxide require intact cardiovascular reflexes. Mongrel dogs were anesthetized with sodium pentobarbital and paralyzed with veruronium bromide. Cardiac output and central blood volume were measured by indocyanine green dilution. Mean circulatory filling pressure, an index of venous tone at constant blood volume, was estimated from the central venous pressure during transient electrical fibrillation of the heart. With intact reflexes, hypoxia (arterial PaO2 = 38 mmHg), hypercapnia (PaCO2 = 72 mmHg), or hypoxic hypercapnia (PaO2 = 41; PaCO2 = 69 mmHg) (1 mmHg = 133.32 Pa) significantly increased the mean circulatory filling pressure and cardiac output. Hypoxia, but not normoxic hypercapnia, increased the mean systemic arterial pressure and maintained the control level of total peripheral resistance. With reflexes blocked with hexamethonium and atropine, systemic arterial pressure supported with a constant infusion of norepinephrine, and the mean circulatory filling pressure restored toward control with 5 mL/kg blood, each experimental gas mixture caused a decrease in total peripheral resistance and arterial pressure, while the mean circulatory filling pressure and cardiac output were unchanged or increased slightly. We conclude that hypoxia, hypercapnia, and hypoxic hypercapnia have little direct influence on vascular capacitance, but with reflexes intact, there is a significant reflex increase in mean circulatory filling pressure.

Animals↗
PubMed1987

Applied potential tomography for non-invasive temperature mapping in hyperthermia.

In the field of hyperthermia for cancer treatment, much effort is being put into the development of non-invasive temperature monitoring so that the trauma of implanting thermocouple or thermistor probes in the patient can be avoided. Preliminary studies investigating the use of applied potential tomography (APT) for this purpose have been reported. APT has the advantages over other tomographic methods that the instrumentation is inexpensive, transportable, and could easily be accommodated in a hyperthermia treatment environment. Moreover, the temperature coefficient of electrical conductivity is large (2% degrees C-1) compared, for example, with the corresponding quantity in CT, the x-ray attenuation coefficient, which changes by only 0.04% degrees C-1. In our experimental system, 16 electrodes were fixed around a cylindrical block of agar simulating a human thigh. The system was driven with 5 mA at 50 kHz. The agar was heated using the 13.56 MHz capacitive system currently in clinical use in this hospital. By relating data sets recorded at different times during heating to a set recorded before heating, images of the temperature change in the agar with time were computed and are presented. The experiment was then repeated in vivo on the thigh of a volunteer.

Agar↗
PubMed2004

Ionic conductances in sustentacular cells of the mouse olfactory epithelium.

The electrical properties of sustentacular cells (SCs) in the olfactory epithelium (OE) were investigated in tissue slices taken from neonatal mice (P0-P4). Conventional whole-cell recordings were obtained from SCs and also from olfactory receptor neurones (ORNs) in situ. SCs had a larger apparent cell capacitance (C(cell)) (18.6 +/- 0.5 pF) than ORNs (4.4 +/- 0.4 pF) and a lower apparent membrane resistance (R(m)) (160 +/- 11 MOmega versus 664 +/- 195 MOmega, respectively). When corrected for a seal resistance of 1 GOmega, these mean R(m) values were increased to 190 MOmega and 2 GOmega in SCs and ORNs, respectively. SCs generated a TTX (1 microm)-resistant voltage-activated Na(+) current (I(Na)) that had a peak density at -38 mV of -44 pA pF(-1) and supported action potential firing. Peak current density of I(Na) in neurones was 510 +/- 96 pA pF(-1). The outward K(+) current in SCs was composed (> 70%) of a TEA (2 mm)-sensitive component that was mediated by the opening of large-conductance (237 +/- 10 pS; BK) channels. The resting leak conductance (g(L)) of SCs was permeable to monovalent cations and anions and was largely inhibited by substitution of external Na(+) with NMDG and by internal F(-) with gluconate. g(L) deactivated up to 50% at potentials negative of -70 mV and was inhibited by 18beta-glycyrrhetinic acid (20 mum). SCs were identified using fluorescent dyes (Lucifer Yellow and Alexa Fluor 488) in the whole-cell patch pipette-filling solution. Our findings indicate that SCs in the OE of neonates are electrically excitable and are distinguishable from neurones by a having a resting g(L).

Animals↗
PubMed1996

Persistent increased threshold of electrical stimulation selective to motor nerve in multifocal motor neuropathy.

In multifocal motor neuropathy (MMN) the threshold of electrical stimulation showed a persistent, marked increase for the motor nerve which decreased after treatment with intravenous immunoglobulin or oral cyclophosphamide; whereas, the threshold was normal for the sensory nerve. This discrepancy of the thresholds for motor and sensory nerves indicates that the increased threshold for motor nerve is not caused by change in perineural capacitance, such as subperi- and endoneural edema or perineural thickening. Inching studies showed that the site of the elevated motor nerve threshold was closely associated with conduction slowing and block. For the cause of the increased threshold, therefore, we suppose the presence of a factor which interferes with reorganization of the nodal property in the remyelinative process or which directly blocks sodium channels where the blood-nerve barrier is impaired in MMN.

Action Potentials↗
PubMed1993

Use of a.c. impedance methods to study the corrosion behaviour of implant alloys.

The a.c. impedance method is a very useful technique for studying the corrosion behaviour of surgical implant alloys. In this article information is presented on how to efficiently and reliably acquire and analyse experimental data through the use of Nyquist, Bode and Rre versus omega Rim plots. Also, experiments were conducted in which 316L stainless steel specimens were subjected to polarization conditions which caused pitting corrosion. The increased surface area caused by the pitting, inferred from a.c. impedance measurements of specimen capacitance, was found to be well correlated with ASTM standard methods for assessment of pitting.

Alloys↗
PubMed1987

Effects of hypoxia and glycolytic inhibition on electrical properties of sheep cardiac Purkinje fibres.

Active and passive electrical properties of sheep cardiac Purkinje fibres were determined using conventional microelectrode techniques. In addition, oxygen tension was monitored immediately adjacent to the fibres with oxygen sensing microelectrodes. Oxygen was withdrawn for 130 min in a glucose-free solution (PO2 less than 15 mmHg), glycogen breakdown inhibited by 2-4-deoxyglucose and the following effects observed: (i) a decrease in action potential duration by as much as 80%; (ii) a decrease in maximal rate of rise of the action potential (Vmax) by 52%; (iii) an increase in internal longitudinal resistance (ri) by 176%; and (iv) a decrease in conduction velocity (theta) by 47%. The magnitude of the effects depended on PO2 (range: 4 to 46 mmHg). In particular, ri was steeply dependent upon the PO2 of the medium (glycogenolysis also inhibited by 2-4-deoxyglucose): ri increased to 470% above control when PO2 was reduced to 4 mmHg versus only a 47% increase in ri at PO2 = 11 mmHg. These effects were largely reversible after re-oxygenation and washout of 2-4-deoxyglucose although the time course of recovery of ri lagged behind that of action potential duration. Similar to previous studies, practically no effect of hypoxia was observed on the electrical properties of Purkinje fibres when glycogenolysis was not inhibited. The measured decrease of theta correlated relatively well with that predicted from linear cable theory using the changes of (i) Vmax and (ii) ri. No significant changes in membrane capacitance and only minor changes in action potential amplitude developed during combined hypoxia and inhibition of glycolysis.

Action Potentials↗
PubMed2004

Scanning electrochemical microscopy, 52. Bipolar conductance technique at ultramicroelectrodes for resistance measurements.

The bipolar conductance, BICON, technique for the measurement of solution resistance, based on the application of microsecond current pulses, as originally described by Enke and co-workers for measurements with conventional electrodes, was extended for use with ultramicroelectrodes, with a focus on its application in scanning electrochemical microscopy (SECM). When the plateau time used to make the measurement lies within the BICON conditions, the solution conductance can be obtained directly from the output without the need for calibration curves. However, decreasing the size of the ultramicroelectrode decreases the range of values that satisfy these conditions, and one must resort to calibration curves to obtain solution conductance from the measured current, which was nevertheless found to be proportional to electrolyte concentration with electrodes as small as 5 mum in diameter. BICON/SECM approach curves over insulating substrates followed SECM negative feedback theory and approach curves in the presence of low (micromolar) or no added electrolyte are possible once the background conductivity is taken into account. Approach curves to a conducting substrate at open circuit potential are influenced by the solution time constant (solution resistance at the electrode tip x electrode double layer capacitance), which is a function of the tip/substrate distance, as well as the substrate size.

Electric Conductivity↗
PubMed1997

Optimized first phase tilt in "parallel-series" biphasic waveform.

INTRODUCTION: A biphasic defibrillation waveform can achieve a large second phase leading-edge voltage by a "parallel-series" switching system. Recently, such a system using two 30-microF capacitances demonstrated better defibrillation threshold than standard waveforms available in current implantable devices. However, the optimized tilt of such a "parallel-series" system had not been defined. METHODS AND RESULTS: Defibrillation thresholds were evaluated for five different biphasic "parallel-series" waveforms (60/15 microF) and a biphasic "parallel-parallel" waveform (60/60 microF) in 12 anesthetized pigs. The five "parallel-series" waveforms had first phase tilts of 40%, 50%, 60%, 70%, and 80% with second phase pulse width of 3 msec. The "parallel-parallel" waveform had first phase tilt of 50% with second phase pulse width of 3 msec. The defibrillation lead system comprised a left pectoral "hot can" electrode (cathode) and a right ventricular lead (anode). The stored energy at defibrillation threshold of the "parallel-series" waveform with first phase tilts of 40%, 50%, 60%, 70%, and 80% was 7.0 +/- 2.1, 6.1 +/- 2.8, 6.8 +/- 2.8, 7.2 +/- 2.9, and 8.4 +/- 3.1 J, respectively. The stored energy of the "parallel-series" waveform with a 50% first phase tilt was 16% less than the nonswitching "parallel-parallel" waveform (7.3 +/- 2.8 J, P = 0.006). CONCLUSIONS: A first phase tilt of 50% maximized defibrillation efficacy of biphasic waveforms implemented with a "parallel-series" switching system. This optimized "parallel-series" waveform was more efficient than the comparable "parallel-parallel" biphasic waveform having the same first phase capacitance and tilt.

Animals↗
PubMed1997

Electroperturbation of the human skin barrier in vitro: II. Effects on stratum corneum lipid ordering and ultrastructure.

In transdermal iontophoresis, drugs can be driven across the skin by electrorepulsion, but their transport can also be enhanced by electrical perturbation of the skin barrier. Our objective was to study perturbing effects of electrical current on human stratum corneum lipid fine structure combining techniques including freeze-fracture electron microscopy. Human stratum corneum was subjected to pulsed constant currents, varying from 0.013-13 mA.cm-2. The voltage across the stratum corneum was high-frequency-sampled and s.c. impedence values derived from it. Upon termination of the current, skin samples were rapidly frozen and processed for freeze-fracture electron microscopy or subjected to X-ray diffraction analysis. Initially a rapid decrease of the resistance and, overall, a rapid increase of the capacitances was observed; generally, these effects became more pronounced with increasing current density. Wide- and small-angle X-ray diffractograms of human stratum corneum exposed for 1 h to the highest current indicated a disordering of both the lateral packaging arrangement and long-range lamellar stacking of the intercellular lipids of stratum corneum. Furthermore, an increase in the stratum corneum hydration level as a result of electrical current application was observed. On electron micrographs of freeze-fracture replicas of human stratum corneum, exposed for 1 h to current densities between 0.013 and 13 mA.cm-2, perturbations of the intercellular lipid structure were observed in accordance with the results of X-ray diffraction; these perturbations aggravated with increasing current density. Together, the data suggest that both the lateral and the longitudinal disordering of the intercellular lipids observed with X-ray diffraction may be responsible for the appearance of perturbed structures observed with freeze-fracture electron microscopy. The lipid disordering may be due to polarization of the lipid head groups induced by the electrical field, followed by mutual repulsion.

Adult↗
PubMed1971

The effects of temperature and ions on the current-voltage relation and electrical characteristics of a molluscan neurone.

1. Current-voltage relations were generated in the Anisodoris giant neurone (G cell) by either current pulses or slow biphasic current ramps.2. Inward-going rectification occurred during hyperpolarization at warm temperatures (10-15 degrees C), but not at cold temperatures (0-5 degrees C) or in the absence of external K.3. Replacing external K with Rb eliminated inward-going rectification in the warm, but produced it in the cold. The removal of external Na, Cl or Ca had no effect upon inward-going rectification.4. At cold temperatures the I-V relation was linear when generated by current pulses, but was non-linear in accordance with the constant field hypothesis when generated by current ramps.5. A high conductance state developed when the membrane was hyperpolarized beyond a critical potential (approximately - 130 mV in the cold, and - 110 mV in the warm) which was dependent upon external Ca, but not upon K, Na or Cl.6. Hysteresis was observed in the ramp-generated I-V relation whenever the cell was polarized into the high conductance state.7. Rectification and the high conductance state appear to involve different mechanisms within the membrane. However, both are dependent upon absolute membrane potential and not the resting potential.8. The axonal-somatic conductance ratio for the G cell was calculated to be between 2 and 10.9. The membrane time constant (200-100 msec) and specific resistance (0.1-1.5 x 10(6) Omega cm(2)) varied with temperature, membrane potential, and external ions in a manner that correlated with changes in the shape of the I-V relation. In addition, the resistance was dependent upon external Ca.10. The K permeability (P(K)), measured during inhibition of inwardgoing rectification, was independent of temperature and membrane potential. However, P(Na) increased with warming.11. The specific capacitance was calculated to be 0.5-1.0 muF/cm(2). The capacitance increased slightly with warming, but was independent of membrane potential and unaffected by reductions in external K or Na.

Animals↗
PubMedDate not supplied

The effect of guidewires during electrosurgical sphincterotomy.

We describe six electrosurgical incidents and one complication which occurred during guidewire-assisted sphincterotomy. Studies were conducted on three types of guidewires: Teflon painted, Teflon sheathed, and polymer coated. Scanning electron micrographs demonstrated surface imperfections in the painted Teflon guidewire coating, which allowed for potential electrical short circuits between cutting wire and guidewire through a septal defect in a double channel catheter. Septal defects were found in 25% (1 of the 4 tested) of the factory fresh sphincterotomes that were used in this study, and in 10% (6 of 57) of those used clinically. Induced current (capacitively coupled) present on the guidewires was measured at 13 to 30 mA for typical sphincterotomy settings. The induced current on sheathed guidewires, without any insulation defects, was measured at less than 1 mA at typical operating powers. As both short circuits and induced currents place the patient at risk for burns or perforation at the distal end of the guidewire, we suggest the use of a Teflon-sheathed rather than Teflon-painted guidewire, if the wire is to be left in place during sphincterotomy. The Teflon sheath offers the thickest insulation, a very low probability of surface defects, and therefore a high index of safety.

Aged↗
PubMed1998

Differential properties of two stably expressed brain-specific glycine transporters.

Clonal cell lines stably expressing the glial glycine transporter 1b (GLYT1b) and the neuronal glycine transporter 2 (GLYT2) from rat brain have been generated and used comparatively to examine their kinetics, ion dependence, and electrical properties. Differential sensitivity of the transporters to sarcosine is clearly exhibited by the clonal cell lines. GLYT2 transports glycine with higher apparent affinity than GLYT1b and is not inhibited by any assayed compound, as deduced by glycine transport assays and electrophysiological recordings. A sigmoidal Na+ dependence of the glycine uptake by the stable cell lines is observed, indicating the involvement of more than one Na+ in the transport process. A more cooperative behavior for Na+ of GLYT2 than GLYT1b is suggested. One Cl- is required for GLYT1b and GLYT2 transport cycles, although GLYT1b shows three times higher affinity for this ion than GLYT2. The number of expressed transporters was sufficient to allow electrophysiological recordings of the uptake current in the two stable cell lines. GLYT2 exhibits more voltage dependence in both its glycine-evoked current and its capacitive currents recorded in the absence of substrate.

Amino Acid Transport Systems, Neutral↗
PubMed1997

Membrane responses to extracellular ATP in rat isolated white adipocytes.

We used whole-cell and perforated-patch voltage-clamp methods to study the membrane electrical properties of isolated rat epididymal and inguinal white adipocytes. We examined cells from both Sprague-Dawley and Zucker lean and Zucker obese (fa/fa) rats. A delayed-rectifier potassium current was present and similar in unstimulated white fat cells from all these sources. The potassium current activated rapidly with depolarization positive to about -30 mV and showed slow inactivation. Stimulation with extracellular ATP activated both hyperpolarizing and depolarizing conductances. ATP exposure also increased cell membrane capacitance by an average of 16%, suggesting that ATP activates exocytosis. Exposure to norepinephrine had little electrophysiological effect. We conclude that white adipocytes are very similar to brown adipocytes in their resting electrophysiological profile and in their responses to extracellular ATP.

Adenosine Triphosphate↗
PubMed1997

Separate determination of the electrical properties of the tonoplast and the plasmalemma of the giant-celled alga Valonia utricularis: vacuolar perfusion of turgescent cells with nystatin and other agents.

In the giant-celled marine algae Valonia utricularis the turgor-sensing mechanism of the plasmalemma and the role of the tonoplast in turgor regulation is unknown because of the lack of solid data about the individual electrical properties of the plasmalemma and the vacuolar membrane. For this reason, a vacuolar perfusion technique was developed that allowed controlled manipulation of the vacuolar sap under turgescent conditions (up to about 0.3 MPa). Charge-pulse relaxation studies on vacuolarly perfused cells at different turgor pressure values showed that the area-specific resistance of the total membrane barrier (tonoplast and plasmalemma) exhibited a similar dependence on turgor pressure as reported in the literature for nonperfused cells: the resistance assumed a minimum value at the physiological turgor pressure of about 0.1 MPa. The agreement of the data suggested that the perfusion process did not alter the transport properties of the membrane barrier. Addition of 16 microM of the H+-carrier FCCP (carbonylcyanide p-trifluoromethoxyphenyhydrazone) to the perfusion solution resulted in a drop of the total membrane potential from +4 mV to -22 mV and in an increase of the area-specific membrane resistance from 6.8 x 10(-2) to 40.6 x 10(-2) Omegam2. The time constants of the two exponentials of the charge pulse relaxation spectrum increased significantly. These results are inconsistent with the assumption of a high-conductance state of the tonoplast (R. Lainson and C.P. Field, J. Membrane Biol. 29:81-94, 1976). Depending on the site of addition, the pore-forming antibiotics nystatin and amphotericin B affected either the time constant of the fast or of the slow relaxation (provided that the composition of the perfusion solution and the artificial sea water were replaced by a cytoplasma-analogous medium). When 50 microM of the antibiotics were added externally, the fast relaxation process disappeared. Contrastingly, the slow relaxation process disappeared upon vacuolar addition. The antibiotics cannot penetrate biomembranes rapidly, and therefore, the findings suggested that the fast and slow relaxations originated exclusively form the electrical properties of the plasmalemma and the tonoplast respectively. This interpretation implies that the area-specific resistance of the tonoplast is significantly larger than that of the plasmalemma (consistent with the FCCP data) and that the area-specific capacitance of the tonoplast is unusually high (6.21 x 10(-2) compared to 0.77 x 10(-2) Fm(-2) of the plasmalemma). Thus, we have to assume that the vacuolar membrane of V. utricularis is highly folded (by a factor of about 9 in relation to the geometric area) and/or contains a fairly high concentration of mobile charges of an unknown electrogenic ion carrier system.

Cell Membrane↗
PubMed1975

[Plethysmographic and in vitro studies of the vasodilator effect of furosemide (Lasix)].

The beneficial effect of furosemide in treatment of chronic and particularly of acute congestive heart failure has been attributed to its potent diuretic action. In recent studies [16], it has been postulated that the effect of this diuretic agent is primarily vascular in origin. The results of venous occlusion plethysmographic experiments (modificated Whitney-gauge technique) carried out in this study on the forearm of 6 healthy men, show that furosemide (40 mg. i.v.) does not influence arterial blood flow (4-5 ml/100 ml tissue - min). In contrast furosemide induces a prompt significant (p less than 0.001) and sustained (about 45 min) increase in venous capacitance (deltaV/100 ml tissue = 15%) and a corresponding decrease in E'. The direct effect of furosemide on vascular muscle tone was studied in vitro on portal vein and aortic strip preparations from 76 male rats. In 18 experiments mechanical and electrical activity (using three pressure electrodes) were simultaneously recorded. The results of the in vitro experiments show: 1. Only extremely high furosemide concentrations (greater than 500 mg/l) induce slight relaxation of aortic strips. 2. Furosemide causes in contrast a marked dose-dependent per cent decrease of the integrated isometric tension in portal vein preparations: 14 mg/l reduce the initial tension (= 100%) to 80%; 35 mg/l to 65%; 70 mg/l to 50% and 100 mg/l to 35%. 3. The venodilating furosemide effect is significantly (p less than 0.001) increased by reduction in external Na+-concentration [Na+]0 to 120 mM though further reduction in the [Na+]0 to 90 mM does not cause additional changes in the relaxation slope. 4. The simultaneous records of electrical activity demonstrate that the relaxing effect of furosemide is based on decreased spike frequency in shortened bursts as well as on pronounced impairment of conduction velocity without relevant changes in pacemaker frequency. These in vitro results are discussed from the point of view that a furosemide induced decrease in Na+-permeability may determine the changes obtained in electrical and mechanical behaviour of portal veins of the rat.

Adult↗