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PubMed1992

[Thermal distribution in the agar phantom by a new intracavitary RF applicator for prostate gland].

Some studies suggest that the prostate gland is one of the most difficult portions of the body to heat up even by radio frequency (RF) capacitive heating, which is well established as a useful means for deep regional hyperthermia because of its non-uniform power absorption. We have developed a new type of intracavitary applicator for RF capacitive heating which can be connected to an 8 MHz RF heating device (Thermotron-RF8). The applicator is a balloon-type catheter which is filled with electrolyte, such as physiological saline, 3% saline or 3% ferrous sulfate solution, and then put between a pair of regular RF capacitive heating electrodes. The heating characteristics of the applicator were examined by using an agar phantom that is electrically equivalent to muscles. When the applicator was connected to the electrode of the RF generator with a copper cord, the balloon filled with electrolyte operated as an inner electrode. The effective hot area around the balloon of the catheter was observed, and the size of the hot area was changed by the kinds of electrolytes used and their concentration. With this adaptive technique, it is possible to maintain an adequate thermal distribution at a tumor in the uterus, urinary bladder and rectum, as well as the prostate gland.

Agar↗
PubMedDate not supplied

[Lipid bilayer with ion channels--a dipole with inductive properties].

A cyclic peptide-alamethicin forms cation selective channels in lipid bilayers. Anomalous behavior of bilayer capacitance observed during impedance measurements of the planar bilayer containing the peptide is reported. The band of the frequencies used is 30-30000 Hz. The bilayer capacitance measured at a given frequency depends on the value of constant voltage applied to the membrane in series with alternating field. The field dependent capacitance has a negative sign and is equivalent to the inductance so far as phase shift angle between voltage and current is considered. Absolute magnitude of the negative capacitance can exceed several times the geometrical capacitance of the bilayer. In the absence of the applied field the alamethicin molecules lie flat on the membrane surface. The applied field tilts the molecules through the hydrocarbon region of bilayer, so that now the long axis of the peptide monomer is perpendicular to the membrane plane. Lateral diffusion of monomers along the membrane plane results in the formation of oligomers-transmembrane ion channels, and appearance of membrane current. The time period between the moment of tilting of monomers across the lipid bilayer and the moment of the channel formation determines the phase shift between voltage and current seen as a negative capacitance during the impedance measurements.

Electric Conductivity↗
PubMed1994

Electrical impedance alterations of red blood cells during storage.

The electrical impedance of blood is determined mainly by the resistance of the plasma (Rp), resistance of the red cell interior fluid (Ri), and capacitance of the cell membranes (Cm). These parameters were measured on 10 stored blood samples consecutively during 4 or 5 weeks of storage at 4 degrees C, once every week. Compared to the values of fresh samples, a statistically significant decrease in Rp was found mainly during the first week of storage, Ri did not decrease significantly until after 3 weeks, whereas Cm decreased progressively with time. These alterations can be explained by known red cell lesions during storage. The results indicate that electrical impedance measurements might be useful for monitoring red cell ageing and assessing the quality of stored red blood cells.

Blood Preservation↗
PubMed1992

Imaging the complex impedance in electrical impedance tomography.

Measuring the reactive component of the bio-impedance enables a full characterisation of the frequency response of a tissue. The amplitude of the reactive component is relatively small in the frequency range generally used in electrical impedance tomography (EIT). Its measurement is therefore more sensitive to errors. At higher frequencies, the amplitude of this component increases, which increases the signal-to-noise ratio. The stray capacitance, however, also increases and the front-end circuit must be designed carefully. The purpose of the present study is to show the feasibility of the collection of data at relatively high frequencies; 31.25 and 250 kHz were used. Both the real and reactive components were used to reconstruct images from capacitive targets. This study suggests that it may be possible to use multifrequency systems to determine the parameters of frequency loci and therefore tissue characterisation.

Electric Conductivity↗
PubMed1994

Theory of electroporation of planar bilayer membranes: predictions of the aqueous area, change in capacitance, and pore-pore separation.

A large increase in the transmembrane voltage, U(t), of a fluid bilayer membrane is believed to result in the occurrence of temporary aqueous pathways ("pores") across the membrane. The number, size, and evolution dynamics of these pores are expected to be crucial to the transport of water-soluble species ranging from small ions to macromolecules such as proteins and nucleic acids. In this paper we use a transient aqueous pore theory to estimate the fraction of the membrane area, Fw(t), which is temporarily occupied by water-filled pores for short square, exponential, and bipolar square pulses. For short pulses, "reversible electrical breakdown" occurs when the transmembrane voltage reaches about 1 V, and Fw(t) is predicted to rise rapidly, but always to be less than 10(-3). The conductance of a large number of pores causes reversible electrical breakdown and prevents a significantly larger U from being reached. Despite the large dielectric constant of water, for reversible electroporation the associated change in membrane capacitance, delta C, due to the pores is predicted to be small. Moreover, for a flat membrane the minimum value of the mean pore-pore separation is large, about 60 times the minimum pore radius. In flat membranes, pores are predicted to repel, but the opposite is expected for curved cell membranes, allowing the possibility of coalescence in cell membranes. For some moderate values of U, rupture (irreversible electrical breakdown) occurs, as one or more supracritical pores expand to the membrane boundary and the entire membrane area becomes aqueous. In all cases it is found that a quantitative description of electroporation requires that a pore size distribution, rather than a single size pore.

Electric Conductivity↗
PubMed1991

Hydrophobic ion transfer between membranes of adjacent hepatocytes: a possible probe of tight junction structure.

The topology of the tight junction is probed by introducing dipicrylamine (dpa-), a lipid-soluble anion, into the membranes of hepatocyte pairs in culture. Once partitioned into the membrane, dpa- ions are free to move in the hydrophobic core of the membrane, where their mobile charges greatly increase membrane capacitance. If tight junctions are lines of membrane fusion, dpa- will cross the tight junction without traversing a polar headgroup layer. Furthermore, the electric potential across the tight junction will be equal to the difference in membrane potentials of the two cells. dpa- can therefore be expected to move electrophoretically from cell membrane to cell membrane across the junction in response to an intercellular voltage difference. Experiments performed under double whole-cell clamp show that this transfer occurs as follows: First, dpa- causes an intercellular current unrelated to gap junctions to flow in response to an intercellular voltage difference. Second, this electrophoretic removal or addition of dpa- from a cell's membrane through the tight junction must reduce or increase its dpa- content and thus its capacitance. Experiments confirm this prediction: We detect rapid, symmetric, and reversible changes in membrane capacitance in response to changes in the membrane potential of the neighboring cell. Finally, we find that hepatocyte membranes contain a negatively charged endogenous molecule that contain a negatively charged endogenous molecule that can move from cell to cell like dpa- under the influence of an intercellular potential difference. We conclude that membrane fusion occurs at tight junctions and that this hydrophobic intercellular pathway can play a role in intercellular communication.

Animals↗
PubMed1999

Characterization of three-dimensional tissue cultures using electrical impedance spectroscopy.

Electrical impedance spectroscopy was used to characterize the cell environment of multilayered cell cultures (MCCs), a culture system in which cells are grown on a permeable support membrane to form a thick disc of cells with tumor-like properties. Cultures were grown using SiHa tumor cells as well as V79 wild-type cells and V79/DOX cells cultivated to exhibit multidrug resistance. Electrical impedance measurements were made on MCCs over a frequency range of 0. 1 kHz to 1 MHz. Data analysis using a simple electrical model for the cell environment yielded estimates for parameters related to the intra- and extracellular resistance and net membrane capacitance, which were then related to MCC thickness. The extracellular fraction and tortuosity of the MCCs were determined in separate experiments where the rate of diffusion and the equilibrium level of C14-inulin, which does not penetrate the cell membrane, was measured within MCCs. Impedance measurements predicted the barrier to diffusion posed by the extracellular space of MCCs to be roughly two times greater than that inferred from the C14-inulin experiments. However, the relative ranking of the three cell types used to grow MCCs was similar for the two methods. Results indicate that impedance spectroscopy is well suited for use in characterizing the MCC cell environment, offering a fast, nondestructive method for monitoring cell culture growth and integrity.

Animals↗
PubMed1990

In vivo measurement of intra- and extracellular space of brain tissue by electrical impedance method.

An impedance method was applied to evaluate transcellular fluid shifts in ischaemic brain oedema. The admittances (apparent electrical conductivities) of tissues were measured at varied frequencies based on a simple model of an electrical equivalent circuit for tissues, which consisted of Re (resistivity of extracellular fluid), Ri (resistivity of intracellular fluid) and Cm (capacitance of cell membrane). Calculated were Re, Ri, Rinf (resistivity of total fluid), Re/Ri and alpha (Cole-Cole distribution index) of brain tissue by Cole-Cole an arc of a circle. During ischaemia induced by cat middle cerebral artery occlusion (MCAO), the parameters were examined continuously. After MCAO, cerebral blood flow (CBF) decreased to under 10 ml/100 g/min. Then Re and Re/Ri increased, but Ri decreased. These results indicated that fluid shift from extracellular (EC) to intracellular (IC) space occurred after ischaemic insult. Rinf showed no changes during ischaemia of 30 min, which demonstrated no changes of total fluid volume. Using this impedance technique, fluid accumulation and shift may be examined by changes of Re, Ri, Re/Ri and Rinf in various types of brain oedema in vivo.

Animals↗
PubMed1997

Emptying of intracellular Ca2+ stores stimulates Ca2+ entry in mouse pancreatic beta-cells by both direct and indirect mechanisms.

1. In non-excitable cells, the depletion of intracellular Ca2+ stores triggers Ca2+ influx by a process called capacitative Ca2+ entry. In the present study, we have investigated how the emptying of these stores by thapsigargin (1 microM) influences Ca2+ influx in electrically excitable pancreatic beta-cells. The cytoplasmic Ca2+ concentration ([Ca2+]i) was monitored in clusters of mouse beta-cells or in whole islets loaded with fura-2. 2. The membrane was first held hyperpolarized by diazoxide, an opener of ATP-sensitive K+ (KATP) channels, in the presence of 4.8 mM K+. Alternating between Ca(2+)-free medium and medium containing 2.5 mM Ca2+ caused a minor rise in [Ca2+]i (approximately 14 nM) in clusters of beta-cells. A larger rise (approximately 65 nM), resistant to the blockade of voltage-dependent Ca2+ channels by D600, occurred when extracellular Ca2+ was readmitted after emptying intracellular Ca2+ stores with thapsigargin or acetylcholine. Thus there exists a small capacitative Ca2+ entry in beta-cells. 3. When the membrane potential was clamped at depolarized levels with 10, 20 or 45 mM K+ in the presence of diazoxide, [Ca2+]i increased to different plateau levels ranging between 100 and 900 nM. Thapsigargin consistently caused a further transient rise in [Ca2+]i, but had little (at 10 mM K+) or no effect on the plateau level. This confirms that the capacitative Ca2+ entry is small. 4. In clusters of cells whose membrane potential was not clamped with diazoxide, 15 mM glucose (in 4.8 mM K+) induced [Ca2+]i oscillations by promoting Ca2+ influx through voltage-dependent Ca2+ channels. The application of thapsigargin accelerated these oscillations and increased their amplitude, sometimes causing a sustained elevation of [Ca2+]i. Similar results were obtained from whole islets perifused with a medium containing > or = 6 mM glucose. The effect of thapsigargin was always much larger than expected from the capacitative Ca2+ entry, probably because of a potentiation of Ca2+ influx through voltage-dependent Ca2+ channels. 5. This potentiating effect of thapsigargin did not result from an acceleration of cell metabolism since the drug did not affect glucose-induced changes in NAD(P)H fluorescence. It is also unlikely to involve the inhibition of KATP channels because thapsigargin steadily elevated [Ca2+]i in cells in which [Ca2+]i oscillations persisted in the presence of a maximally effective concentration of tolbutamide. 6. In conclusion, the emptying of intracellular Ca2+ stores in beta-cells induces a small capacitative Ca2+ entry and activates a depolarizing current which potentiates glucose-induced Ca2+ influx through voltage-dependent Ca2+ channels.

Acetylcholine↗
PubMed2004

Fish perform spatial pattern recognition and abstraction by exclusive use of active electrolocation.

The field generated by the electric organ of weakly electric fish varies with the electrical properties of nearby objects. Correspondingly, current fluxes in this field differentially stimulate the electroreceptors in the fish's skin. Thus, resistors are to conductors and insulators as gray is to black and white in optics. Additionally, the capacitances of plants and insect larvae contrast with those of water or stones, giving effects comparable to "coloration". Receptors arrayed over a large area of the skin act like a retina upon which the discharge projects "electric images". By further central processing, the fish also discriminate between objects according to their composition, size, or distance, a procedure termed "electrolocation", analogous to echolocation in bats. Here we demonstrate that G. petersii and S. macrurus can also recognize 3D orientations and configurations and extract and generalize spatial features solely with their electrical sense. We presented fish with virtual electrical "objects" formed from electrodes set flush in the inner surface of a Y maze with various patterns of external connectivity. With reward and aversion training, the fish could recognize similar electrode configurations and extract a feature, e.g., a vertical connectivity, present in various novel configurations. Previously, shape recognition has only been shown in electrolocating fish when they are in full mechanical contact with solid objects.

Animals↗
PubMed2001

An ultrathin platinum film sensor to measure biomolecular binding.

A sensitive conductimetric immunosensor has been demonstrated based on an ultrathin platinum film on an oxidized silicon base. The film is about 25 A thick and is seen to consist of a discontinuous layer with channels 20-30 A wide. Monoclonal antibodies were bound to the sensor surface using conventional biosensor chemistry. Impedance at fixed frequencies across the film was used to track modification and binding at the surface. Impedance increased 55% at 20 Hz during the activation of the surface with anti-alkaline phosphatase (anti-AP). Binding of alkaline phosphatase (AP) to the prepared surface results in a further increase of 12%. p-Nitrophenyl phosphate hydrolysis confirmed binding and activity of the AP. About 40 amol AP were bound on the 0.5 cm(2) electrode. Non-specific binding of horseradish peroxidase caused an impedance change <6%. Control experiments showed small impedance changes and trace enzyme activity. Since the mechanism of electrical conduction of the thin film was not established, modeling of thin-film response was used to distinguish between redox processes, capacitance and tunneling mechanisms. The data fit well with the diffusion distributed elements (DE) model as well as a transmission line distribution element (DX) model. The first model, DE, is distributed elements for diffusion. The second DX model represents a transmission line. The sensors behave in a distributed network or like a transmission line.

Alkaline Phosphatase↗
PubMedDate not supplied

[Changes in the electrical and visco-elastic properties of bilayer lipid membranes during interaction with proteins and lipoproteins].

A method for simultaneous registration of planar bilayer lipid membrane (BLM) DC conductance G, capacitance C, surface potential difference delta phi and transversal elasticity module E is developed. C, delta phi and E are proportional to the amplitude of the first, second and third harmonics of capacitance current respectively. A comparative study of the interaction of BLM with very low density lipoproteins (VLDL), influenza virus matrix protein (M-protein) and yeast invertase was carried out. The kinetics of delta phi, E and G changes at different concentrations of VLDL, and dependence of delta phi and G on M-protein and invertase concentration was investigated. It is shown for VLDL invertase and M-protein that the changes in delta phi and E occur before the change in G. The method used permits to study peculiarities of individual stages of interaction between charge particles, supramolecular structures and lipid membranes.

Chemical Phenomena↗
PubMed2002

Spontaneous rhythmicity in cultured cell clusters isolated from mouse small intestine.

To investigate spontaneous rhythmicity in smooth muscle tissue, we have developed a cell cluster preparation. Cell clusters were enzymatically isolated from the muscle layer of mouse small intestine and cultured for several days. They included smooth muscle, neurones, and c-Kit-immunopositive interstitial cells. c-Kit-immunopositive cells in myenteric plexus, showing a networklike structure, are putative pacemaker cells. The cultured cell clusters routinely show spontaneous contraction and preserve characteristic features in this tissue: (1) high temperature dependency of contractile frequency; (2) spontaneous electrical activities measured with patch clamp techniques are insensitive to tetradotoxin (TTX) and dihydropyridine Ca(2+) antagonists. This preparation could therefore be used as a good model system to investigate the underlying mechanisms of intestinal motility and pacemaker function. The relationship between the frequency of electrical activity and cluster size suggests that the minimum unit of small intestine tissue to yield normal pacemaker activity is approximately 100 microm in diameter, or less. The applications of 100-120 microM Cd(2+) and Ni(2+) significantly suppressed the spontaneous activity. Ca(2+) influx pathways other than L-type and "classical" T-type voltage-sensitive Ca(2+) channels seem very likely to play an important role, such as nonselective cation channels and capacitative Ca(2+) entry. Furthermore, applications of heptanol reduced the amplitude and the frequency of the oscillating inward currents and eventually terminated them, suggesting that electrical cell-to-cell coupling may also make some contribution to the generation of spontaneous activity.

Anesthetics, Local↗