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PubMed1989

Dielectric properties of mouse lymphocytes and erythrocytes.

In order to study the effect of the nucleus on dielectric behavior of the whole cell, permittivity (dielectric constant) and conductivity of mouse lymphocytes and erythrocytes were measured over a frequency range from 0.1 to 250 MHz. Erythrocytes (spherocytes) showed a single dielectric dispersion, which was explained by a single-shell model that is a conducting sphere covered with a thin insulating shell. On the other hand, lymphocytes showed a broad dielectric dispersion curve which was composed of two subdispersions. The high-frequency subdispersion, which was not found for erythrocytes, was assigned to the Maxwell-Wagner dispersion of the nucleus occupying about 65% of the total cell volume. Analysis of the lymphocyte dispersion was carried out by a double-shell model, in which a shelled sphere, i.e., nucleus, is incorporated into the single-shell model. The following electrical parameters were consequently estimated; the capacitance of the plasma membrane, 0.86 microF.cm-2; the conductivity of the cytoplasm, 3.2 mS.cm-1; the capacitance and conductance of the nuclear envelope are, respectively, 0.62 microF.cm-2 and 15 S.cm-2, and the permittivity and conductivity of the nucleoplasm are 52 and 13.5 mS.cm-1.

Algorithms↗
PubMed2003

Electroporation: theory and methods, perspectives for drug delivery, gene therapy and research.

Electroporation designates the use of short high-voltage pulses to overcome the barrier of the cell membrane. By applying an external electric field, which just surpasses the capacitance of the cell membrane, transient and reversible breakdown of the membrane can be induced. This transient, permeabilized state can be used to load cells with a variety of different molecules, either through simple diffusion in the case of small molecules, or through electrophoretically driven processes allowing passage through the destabilized membrane--as is the case for DNA transfer. Initially developed for gene transfer, electroporation is now in use for delivery of a large variety of molecules: From ions to drugs, dyes, tracers, antibodies, and oligonucleotides to RNA and DNA. Electroporation has proven useful both in vitro, in vivo and in patients, where drug delivery to malignant tumours has been performed. Whereas initial electroporation procedures caused considerable cell damage, developments over the past decades have led to sophistication of equipment and optimization of protocols. The electroporation procedures used in many laboratories could be optimized with limited effort. This review (i) outlines the theory of electroporation, (ii) discusses factors of importance for optimization of electroporation protocols for mammalian cells, (iii) addresses particular concerns when using electroporation in vivo, e.g. effects on blood flow and considerations regarding choice of electrodes, (iv) describes DNA electrotransfer with emphasis on use in the in vivo setting, and (v) sums up data on safety and efficacy of electroporation used to enhance delivery of chemotherapy to tumours in cancer patients.

Animals↗
PubMed2003

Impaired insulin secretion and glucose tolerance in beta cell-selective Ca(v)1.2 Ca2+ channel null mice.

Insulin is secreted from pancreatic beta cells in response to an elevation of cytoplasmic Ca(2+) resulting from enhanced Ca(2+) influx through voltage-gated Ca(2+) channels. Mouse beta cells express several types of Ca(2+) channel (L-, R- and possibly P/Q-type). beta cell-selective ablation of the gene encoding the L-type Ca(2+) channel subtype Ca(v)1.2 (betaCa(v)1.2(-/-) mouse) decreased the whole-cell Ca(2+) current by only approximately 45%, but almost abolished first-phase insulin secretion and resulted in systemic glucose intolerance. These effects did not correlate with any major effects on intracellular Ca(2+) handling and glucose-induced electrical activity. However, high-resolution capacitance measurements of exocytosis in single beta cells revealed that the loss of first-phase insulin secretion in the betaCa(v)1.2(-/-) mouse was associated with the disappearance of a rapid component of exocytosis reflecting fusion of secretory granules physically attached to the Ca(v)1.2 channel. Thus, the conduit of Ca(2+) entry determines the ability of the cation to elicit secretion.

Animals↗
PubMed1990

The effect of halothane on norepinephrine responsiveness in rabbit small mesenteric veins.

The effect of halothane on the response of small isolated mesenteric capacitance veins to exogenous norepinephrine and electrically induced endogenous norepinephrine release was studied. The role of extra- and intracellular Ca2+ in norepinephrine-induced contractions was also examined. Two-millimeter-long segments from the second-order branch of the mesenteric vein were stretched to twice their resting diameter, and the generated tension was measured with a force transducer. Dose-dependent effects of norepinephrine on generated tension were examined before and after exposure to 0.75 and 1.5% halothane. (These concentrations produced perfusate halothane concentrations of 0.31 and 0.49 mM respectively.) Norepinephrine produced an increase in the basal vessel tension along with a superimposed rhythmic oscillation in tension. Although the magnitude of the tension increase was not affected by either concentration of halothane, the amplitude of the oscillations was reduced. Ryanodine (a blocker of Ca2+ release from the sarcoplasmic reticulum), like halothane, decreased the amplitude of the oscillations, but did not affect overall tension development. In the Ca2(+)-free medium the contractile response to norepinephrine was greatly attenuated as compared to control, whereas the oscillatory behavior was completely abolished. Norepinephrine release was examined indirectly by measuring the increase in tension during electric field stimulation. Response to endogenously released norepinephrine was significantly decreased by exposure to halothane 1.5% (0.49 mM) and blocked by pretreating the vessel with phentolamine. At concentrations used clinically, halothane did not affect overall developed tension in response to exogenously applied norepinephrine. However, 1.5% (0.49 mM) halothane decreased both sarcoplasmic-reticulum-dependent oscillations in tension and electrically induced release of endogenous norepinephrine.

Animals↗
PubMed2006

Evidence for p-type doping of InN.

The first evidence of successful p-type doping of InN is presented. It is shown that InN:Mg films consist of a p-type bulk region with a thin n-type inversion layer at the surface that prevents electrical contact to the bulk. Capacitance-voltage measurements indicate a net concentration of ionized acceptors below the -type surface. Irradiation with 2 MeV He+ ions is used to convert the bulk of InN:Mg from p to n-type, at which point photoluminescence is recovered. The conversion is well explained by a model assuming two parallel conducting layers (the surface and the bulk) in the films.

Journal Article↗
PubMed1973

The attenuation of passively propagating dendritic potentials in a motoneurone cable model.

1. The Rall model of the motoneurone, which consists of a lumped resistance and capacitance, representing the soma, in parallel with a number of distributed resistance-capacitance networks of finite and equal electrical length, representing equivalent dendritic cables, has been used to study the effects of varying electrical and geometrical parameters on the time course and amplitude of transients generated at different locations on the dendritic cables.2. An analytical solution has been obtained for the time course of the voltage transient generated at the point of current injection on the parallel combination of all dendritic cables, in terms of the distance from the soma to the current injection point, the electrotonic length of the equivalent dendritic cable, the dendritic to soma conductance ratio and the membrane time constant. The current applied is a current impulse, and the response to any synaptic current time course may be obtained from the analytical expression for the current impulse response. A smooth current time course of the form Te(-alphaT) has been used in computations.3. An analytical expression has been obtained for the early part of the voltage response at the point of current injection, when the current is applied to a fraction of the total dendritic cable. This response is in terms of all the cable parameters, and the assumed fraction of the dendritic cable which receives the synaptic current. Computations of this response have been carried out assuming a smooth time course of synaptic current.4. The computations of the peak amplitude of the voltage transient obtained from these expressions, together with similar computations for the peak amplitude of the voltage transient after propagation to the soma (Jack & Redman, 1971b), have been used to derive a set of attenuation curves for dendritic propagation. These curves give the ratio of the peak amplitude of the voltage transient at the synaptic location on the dendritic cable, and the peak amplitude after propagation to the soma, in terms of the electrotonic distance to the synaptic location, the time course of current injection, and the cable parameters for the motoneurone model.

Action Potentials↗
PubMed2000

Measured capacitance of a condenser microphone as a function of diaphragm displacement

This paper shows that the capacitance of a polarized condenser microphone measured with a sinusoidal electrical signal is quantitatively related to the displacement of the microphone diaphragm. In fact, the capacitance measured with an ac signal is the "input capacitance" of the microphone when it acts as a transmitter. The expressions for the diaphragm displacement and the input capacitance are derived with damping taken into account. The input capacitance differs from the static capacitance with bias by an additional term which varies with the polarization voltage and frequency. Therefore, in general, it is impossible to measure the static capacitance with bias using a low frequency ac signal without the diaphragm being blocked. In order to measure the true static capacitance with bias, a static method based on the dc voltage distribution is presented. The experimental results for the input capacitance and the static capacitance with bias, obtained with the abovementioned ac and dc methods, respectively, give a high level of confidence in the theory. The experimental results reported by some others also support the theory.

Journal Article↗
PubMed1985

Responses of left ventricle to changes in aortic input impedance.

In order to evaluate how pressure and flow at the outlet of a ventricle are determined by the interaction between the ventricle and an aortic input impedance, we examined the effects of independent changes in the peripheral resistance and in the aortic compliance using isolated canine left ventricle preparations. There was an inverse linear relationship of mean values between pressure and cardiac output under pure resistance changes when coronary flow was maintained constant. But, when the coronary perfusion pressure depended on mean aortic pressure, the relationship was no longer linear under a critical aortic pressure. When aortic compliance was increased, late systolic flow was enhanced and late systolic pressure decreased such that the stroke volume increased. The top part of the pressure-volume loop showed a configurational change from the right side down to the left side down. Changes in pressure and flow wave forms, and in the pressure-volume loop can be predicted by an electrical model in which time varying capacitance arranged in series with the internal resistance was used as a ventricular model.

Animals↗
PubMed2001

Electrical impedance scanning: a new technique in the diagnosis of lymph nodes in which malignancy is suspected on ultrasound.

Differentiation between inflammatory and malignant lymph nodes by ultrasound is difficult. Electrical impedance scanning (EIS) is a new diagnostic tool, so far used primarily for the identification of malignant breast lesions. Cancer cells have altered dielectric properties compared with normal cells, thereby distorting the local electrical field. The induced changes in capacitance and conductivity are measurable using EIS. We evaluated EIS in demonstrating the cause of lymph node enlargement. 51 lymph nodes that were suspicious for malignancy on ultrasound (32 patients, mean age 32 years), with a mean size of 18 mm x 12 mm x 10 mm, were examined. The following lymph node locations were included in the study: cervical, inframandibular, axillary, paraaortic and inguinal. EIS results were compared with histopathological and follow-up findings. 30/34 malignant lymph nodes were correctly detected using EIS, while 14/17 inflammatory or benign lymph nodes were correctly identified as benign by EIS; thus, there were 4/51 false negative and 3/51 false positive cases. The sensitivity was 88.2% and the specificity was 82.4%. Corresponding negative and positive predictive values were 77.8% and 90.9%, respectively. Results from this initial study suggest the potential usefulness of EIS as an adjunctive imaging modality in the differentiation of lymphadenopathy that is equivocal on ultrasound. The best accuracy was obtained in the cervical, axillary and inguinal regions. Owing to technical restrictions of the present system, examination of inframandibular and paraaortic lymph nodes should be limited to special cases.

Adult↗
PubMed2005

Electroporation: introduction and expression of transgenes in plant protoplasts.

An optimized protocol for the electroporation-based transfection of tobacco protoplasts is described that routinely results in transgene expression frequencies approaching 90%. The overall efficiency of the procedure depends collectively on numerous key parameters, including protoplast viability; DNA concentration, purity, and topology; carrier DNA; and electrical conditions such as ionic strength of the electroporation buffer, electric field strength, pulse duration, and capacitance. Individual methodologies that address each one of these parameters are presented in sufficient detail to enable successful reproduction of this method along with notes that describe helpful tips.

Electroporation↗
PubMedDate not supplied

New applications of electrical impedance of human blood.

The electrical impedance parameters of human blood, that is, plasma resistance Rp, cell interior resistance Ri and cell membrane capacitance Cm, were determined by measuring impedance amplitudes at three different frequencies, 0.1, 0.8 and 1.2 MHz. Several new findings have been obtained. The fibrinogen in normal blood raised Rp and Cm by about 4% and 20%, respectively, and serum proteins contributed to the capacitance by about 14%. The results imply that the electrical impedance of blood may reflect certain diseases that involve abnormal compositions of certain plasma proteins. Measurement on 62 samples with various erythrocyte sedimentation rates (ESR) demonstrated that both Rp and Cm were proportional to ESR, implying that the impedance measurement might be an alternative method for quick estimation of ESR. During in vitro storage of blood at 4 degrees C, both Rp and Cm decreased with time, about -20% for Cm after four weeks of storage. The results imply that the impedance change might be a useful index for evaluating the quality of stored blood.

Blood Physiological Phenomena↗
PubMed1991

The influence of a single application of different moisturizers on the skin capacitance.

Moisturizers are believed to improve the skin condition by increasing the water content of the stratum corneum. A variety of techniques for assessing skin hydration has been developed. In the present study the capacitance following a single application of different moisturizers to normal skin on 12 volunteers was measured with the commercial available Corneometer 420. The moisturizers were pure petrolatum and three oil-in-water creams. The latter contained either glycerine, glycerine and pyrollidone carboxylic acid, or urea as humectant agents. The first measurement of the change in the capacitance was done 2 h after application of the products. All tested products increased the capacitance in the same order of magnitude. For the creams the values were significantly enhanced during the experimental period (6 h). Excess product were removed from some skin areas after the 2 h measurement. This caused immediately a significant decrease in the capacitance of the cream treated sites, whereas a tendency towards higher values were noted on the petrolatum-treated sites. These findings indicate that the non-absorbed components influences the capacitance values. Hence, the interpretation of electrical measurements with respect to skin moisture should be made with caution.

Adult↗
PubMed2003

Outer hair cell piezoelectricity: frequency response enhancement and resonance behavior.

Stretching or compressing an outer hair cell alters its membrane potential and, conversely, changing the electrical potential alters its length. This bi-directional energy conversion takes place in the cell's lateral wall and resembles the direct and converse piezoelectric effects both qualitatively and quantitatively. A piezoelectric model of the lateral wall has been developed that is based on the electrical and material parameters of the lateral wall. An equivalent circuit for the outer hair cell that includes piezoelectricity shows a greater admittance at high frequencies than one containing only membrane resistance and capacitance. The model also predicts resonance at ultrasonic frequencies that is inversely proportional to cell length. These features suggest all mammals use outer hair cell piezoelectricity to support the high-frequency receptor potentials that drive electromotility. It is also possible that members of some mammalian orders use outer hair cell piezoelectric resonance in detecting species-specific vocalizations.

Animals↗
PubMed1996

Electrosurgical Injuries in Gynecologic Laparoscopy

We reviewed the 396 operative laparoscopies performed from March 1994 to March 1996 to determine the numbers and causes of electrical injuries. Electrical injuries were reported in four (1.01%) patients. Capacitive coupling induced by a laparoscope inserted through a conductive cannula sleeve with a nonconductive collar caused two bowel injuries that required laparotomy. Insulation failure of an electric cable resulted in a skin burn. A small surface contact area of a cannula sleeve being pulled out of the abdominal wall led to a surface burn in the abdominal wall. Lack of knowledge and insufficient attention on the part of laparoscopic surgeons and operating room personnel may result in electrosurgical accidents.

Journal Article↗
PubMed1995

Theoretically optimal duty cycles for chest and abdominal compression during external cardiopulmonary resuscitation.

OBJECTIVE: To use an electronic model of human circulation to compare the hemodynamic effects of different durations of chest compression during external CPR, both with and without interposed abdominal compression (IAC). METHODS: An electrical analog model of human circulation was studied on digital computer workstations using SPICE, a general-purpose circuit simulation program. In the model the heart and blood vessels were represented as resistive-capacitive networks, pressures as voltages, blood flow as electric current, blood inertia as inductance, and cardiac and venous valves as diodes. External pressurization of the heart and great vessels, as would occur in IAC-CPR, was simulated by the alternate application of damped rectangular voltage pulses, first between intrathoracic vascular capacitances and ground, and then between intra-abdominal vascular capacitances and ground. With this model compression frequencies of 60, 80, and 100 cycles/min and duty cycles ranging from 10% to 90%, both with and without IAC, were compared. RESULTS: There was little difference in hemodynamics when the overall compression frequency was varied between 60 and 100 cycles/min, but the effects of duty cycle were substantial. During both standard CPR and IAC-CPR, total flow and coronary flow were greatest at chest compression durations equal to 30% of cycle time. Interposed abdominal compression substantially improved simulated systemic blood flow and perfusion pressure at all duty cycles, compared with standard CPR without abdominal compression. Mean arterial pressure > 75 mm Hg and artificial cardiac output > 2.0 L/min could be generated by 30% duty cycle compression with IAC. Coronary perfusion in the model is clearly optimized at 30% chest compression (i.e., high-impulse chest compression technique). CONCLUSION: Combined high-impulse chest compressions and IACs maximize blood flow during CPR in the electrical analog model of human circulation.

Abdomen↗
PubMed1981

Capacitive and inductive low frequency impedances of Necturus gallbladder epithelium.

The electrical impedance of Necturus gallbladder epithelium was analysed in the frequency range 0.24 Hz to 6,323 Hz. Under control conditions (NaCl-Ringer's on both sides), the impedance function yields a semicircle with depressed center. When serosal Na+ was replaced by K+, an inductive low frequency (LF) component appeared in the impedance locus. With KCl-Ringer on the mucosal side a second circular arc was observed at frequencies below 1 Hz. The resistive parts of the capacitive and inductive LF components increased after application of TAP+ to the mucosal side. Both LF features were abolished after application of 5 mM TEA+ to the mucosal medium as well as after acidification of the mucosal side. The LF components were depressed by addition of 5 mM Ba2+ to the mucosal solution. As TEA+ blocks apical K+ channels (Van Driessche and Gögelein 1978), it is concluded that the capacitive as well as the inductive LF components are related to transcellular K+ flow. With KCl-Ringer on the mucosal side, mucosa negative potentials increased the equivalent resistance and decreased the equivalent capacitance of the LF impedance. With serosal KCl-Ringer, negative potentials evoked a capacitive component which overlapped with the inductive component observed at open circuit conditions. Positive potentials, however, abolished the capacitive as well as the inductive LF component, elicited by mucosal or serosal KCl-Ringer, respectively. These results demonstrate that serosa to mucosa directed K+ flow causes an inductive LF feature and that mucosa negative potentials elicit a capacitive LF component.

Animals↗