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PubMed1993

Osseous implant for studies of biomaterials using an in vivo electrochemical transducer.

The in vitro and in vivo electrochemical behavior of commercially pure titanium (cp Ti) was characterized using a specialized osseous implant in conjunction with electrochemical impedance spectroscopy (EIS) measurement techniques. Studies performed in vitro were used to verify the operation of the transducer and develop methods of deconvoluting EIS data. This method was subsequently used to describe an electrochemical equivalent circuit model of the surface oxide and electrical double-layer capacitance of cp Ti in the endogenous electrolyte found in the medullary compartment of a baboon tibia. Kinetic profiles of the double-layer capacitance and the polarization resistance were constructed from multiple in vitro and in vivo EIS measurements performed over 60 min at 0 V (reference Ag/AgCI) conditioning potential. The profiles demonstrated that the growth of surface oxides was biphasic, with rapid decrease in the double-layer capacitance occurring within 20 min and reaching steady-state conditions at approximately 40 min. These data suggested that a passive, stable biofilm formed on the cp Ti surface in vivo and in vitro.

Animals↗
PubMed2007

Quantification of the heterogeneity in breast cancer cell lines using whole-cell impedance spectroscopy.

PURPOSE: Quantification of the heterogeneity of tumor cell populations is of interest for many diagnostic and therapeutic applications, including determining the cancerous stage of tumors. We attempted to differentiate human breast cancer cell lines from different pathologic stages and compare that with a normal human breast tissue cell line by characterizing the impedance properties of each cell line. EXPERIMENTAL DESIGN: A microelectrical impedance spectroscopy system has been developed that can trap a single cell into an analysis cavity and measure the electrical impedance of the captured cell over a frequency range from 100 Hz to 3.0 MHz. Normal human breast tissue cell line MCF-10A, early-stage breast cancer cell line MCF-7, invasive human breast cancer cell line MDA-MB-231, and metastasized human breast cancer cell line MDA-MB-435 were used. RESULTS: The whole-cell impedance signatures show a clear difference between each cell line in both magnitude and phase of the electrical impedance. The membrane capacitance calculated from the impedance data was 1.94 +/- 0.14, 1.86 +/- 0.11, 1.63 +/- 0.17, and 1.57 +/- 0.12 muF/cm(2) at 100 kHz for MCF-10A, MCF-7, MDA-MB-231, and MDA-MB-435, respectively. The calculated resistance for each cancer cell line at 100 kHz was 24.8 +/- 1.05, 24.8 +/- 0.93, 24.9 +/- 1.12, and 26.2 +/- 1.07 MOhm, respectively. The decrease in capacitances of the cancer cell lines compared with that of the normal cell line MCF-10A was 4.1%, 16.0%, and 19.1%, respectively, at 100 kHz. CONCLUSIONS: These findings suggest that microelectrical impedance spectroscopy might find application as a method for quantifying progression of cancer cells without the need for tagging or modifying the sampled cells.

Breast Neoplasms↗
PubMedDate not supplied

In vivo noninvasive evaluation of hairless rat skin after high-voltage pulse exposure.

Short high-voltage pulses have recently been shown to dramatically increase and expedite transdermal drug transport via a mechanism hypothesized to involve electroporation. This study addresses tolerance issues of the method in vivo in hairless rat. Chromametry, transepidermal water loss (TEWL), laser Doppler flowmetry (LDF) and corneometry were jointly used for noninvasive sensing of skin biophysical parameters. Slight increases in skin redness, TEWL and LDF values followed the application of electric pulses. The changes in skin capacitance were nonsignificant. The magnitude of the alterations depended on the electrical features of the pulses. When compared to iontophoresis, high-voltage pulses did not induce stronger alterations of skin functions. This report provides the first in vivo demonstration of the safety of the high-voltage pulses proposed for transdermal delivery.

Animals↗
PubMed1992

Relationship between electroporation conditions, electropermeability and respiratory activity for Frankia strain ACN14a.

The use of electroporation for introducing macromolecules into intact cells of the actinomycete Frankia was investigated. Electropermeability was demonstrated by the uptake of dextran (70 kDa) molecules labeled with fluorescein isothiocyanate (FITC) inside Frankia cells. Upon pulsation with an exponentially decaying electric field, the cell membranes became permeable. Loading increased with initial pulsed electric field strength and capacitance. Increased loading efficiency was inversely related to INT (2-(p-iodophenyl-3-(p-nitrophenyl)-5- phenyltetrazolium chloride) reduction activity (respiring bacteria) of the cell population. The presence of CaCl2 in the electroporation and resealing buffer raised INT-reduction activity but K2SO4 decreased this activity. Resealing of electropores was confirmed by a decreasing FITC-dextran loading through the recovery period. The use of FITC-dextran molecules and INT-reduction assay are two new approaches for the study of permeabilization and cellular activity of electroporated bacteria.

Actinomycetales↗
PubMed1981

Impedometric properties of the vulvar and vaginal tissues of ewes during the oestrous cycle.

Tissue electrical conductance (G) and capacitance (C) were measured in vulvar and vaginal tissues of ewes by a spectroimpedographic method at frequencies from 10 Hz to 100 kHz. The calculated specific conductance (mumho/cm) at 100 kHz was 3082 +/- 20 (s.e.m.) in oestrus and 2153 +/- 16 in dioestrus (n = 8) (P < 0.001). The impedance angle and the tissue phase angle increased during oestrus, indicating that cell volume increased and cell density decreased in comparison with dioestrus. The ratio of conductivities at higher and lower frequencies showed that extracellular water content was maximal during oestrus and coincided with standing heat.

Animals↗
PubMed1985

The extremely low frequency electrical properties of plant stems.

The electrical properties (variation of capacitance and conductance with frequency) of a plant stem can be conveniently measured in vivo by time domain dielectric spectroscopy. In this technique a voltage step is applied to a stem. The resulting polarization current is sampled by a microprocessor and Fourier-transformed to yield these properties. Spectra were obtained for seven electrode separations along a Poinsettia stem. The inverse capacitance and conductance were plotted vs separation for 50 frequencies from .35 to 350 Hz. Least-square fits yielded the effective dielectric constant and conductivity of the stem over this frequency range. In this way electrode effects were eliminated. A similar procedure was carried out for Coleus. A log-log plot of dielectric constant vs frequency shows a two-stage linear decrease for both plants. The conductivity is primarily DC. The dielectric loss decreases smoothly with frequency for Coleus. These results are compared to those for bone and the inorganic material hollandite. The dielectric properties seem best described by a cooperative, many-body approach.

Electric Conductivity↗
PubMed1991

Electroporation of lymphoid cells: factors affecting the efficiency of transfection.

We have increased the efficiency of electroporation of lymphoid cells over fifty fold by optimising several biological and electrical parameters. Under optimised conditions, the electroporation efficiency was comparable to that reported for other cell types. Actively dividing cells were crucial for high transient transfection signal. The two most important electrical parameters were high capacitance (960 microF) and moderate decay constants in the range of 10-15 ms. The optimal field strength depended on the cell line, but was in the range 0.6-1 kV/cm. Administering the pulse in medium lacking serum gave higher efficiency than when isotonic salt solution was used and the transfection signal was depressed if cells and DNA were allowed to incubate for several minutes either before or after the pulse. Electroporation was carried out at room temperature and there was no advantage in using low temperatures (0-4 degrees C). When electroporated cells were grown in conditioned medium, the signal was enhanced about two fold depending on the source of the conditioned medium.

Animals↗
PubMed1990

Demonstration of the electrogenicity of proton translocation during the phosphorylation step in gastric H+K(+)-ATPase.

Membrane fragments containing the H+K(+)-ATPase from parietal cells have been adsorbed to a planar lipid membrane. The transport activity of the enzyme was determined by measuring electrical currents via the capacitive coupling between the membrane sheets and the planar lipid film. To initiate the pump currents by the ATPase a light-driven concentration jump of ATP from caged ATP was applied as demonstrated previously for Na+K(+)-ATPase (Fendler, K., Grell, E., Haubs, M., Bamberg, E. 1985. EMBO J. 4:3079-3085). Since H+K(+)-ATPase is an electroneutrally working enzyme no stationary pump currents were observed in the presence of K+. By separation of the H+ and K+ transport steps of the reaction cycle, however, the electrogenic step of the phosphorylation could be measured. This was achieved in the absence of K+ or at low concentrations of K+. The observed transient current is ATP dependent which can be assigned to the proton movement during the phosphorylation. From this it was concluded that the K+ transport during dephosphorylation is electrogenic, too, in contrast to the Na+K(+)-ATPase where the K+ step is electroneutral. The transient current was measured at different ionic conditions and could be blocked by vanadate and by the H+K(+)-ATPase specific inhibitor omeprazole. An alternative mechanism for activation of this inhibitor is discussed.

Adenosine Diphosphate↗
PubMed2004

Inner field compensation as a tool for the characterization of asymmetric membranes and Peptide-membrane interactions.

Symmetric and asymmetric planar lipid bilayers prepared according to the Montal-Mueller method are a powerful tool to characterize peptide-membrane interactions. Several electrical properties of lipid bilayers such as membrane current, membrane capacitance, and the inner membrane potential differences and their changes can be deduced. The time-resolved determination of peptide-induced changes in membrane capacitance and inner membrane potential difference are of high importance for the characterization of peptide-membrane interactions. Intercalation and accumulation of peptides lead to changes in membrane capacitance, and membrane interaction of charged peptides induces changes in the charge distribution within the membrane and with that to changes in the membrane potential profile. In this study, we establish time-resolved measurements of the capacitance minimization potential DeltaPsi on various asymmetric planar lipid bilayers using the inner field compensation method. The results are compared to the respective ones of inner membrane potential differences DeltaPhi determined from ion carrier transport measurements. Finally, the time courses of membrane capacitances and of DeltaPsi have been used to characterize the interaction of cathelicidins with reconstituted lipid matrices of various Gram-negative bacteria.

Antimicrobial Cationic Peptides↗
PubMed1992

Dendritic morphology of pyramidal neurones of the visual cortex of the rat. IV: Electrical geometry.

Features of the dendritic morphology of pyramidal neurones of the visual cortex of the rat that are relevant to the development of models of their passive electrical geometry were investigated. The sample of 39 neurones that was used came from layers 2/3 and 5. They had been recorded from and injected intracellularly with horseradish peroxidase (HRP) in vitro as part of a previous study (Larkman and Mason, J. Neurosci 10:1407, 1990). These cells had been reconstructed and measured previously by light microscopy. The relationship between the diameters of parent and daughter dendrites during branching was examined. It was found that most dendrites did not closely obey the "3/2 branch power relationship" required for representation of the dendrites as single equivalent cylinders. Estimates of total neuronal membrane area ranged from 27,100 +/- 7,900 microns2 for layer 2/3 cells to 52,200 +/- 11,800 microns2 for thick layer 5 cells. Dendritic spines contributed approximately half the total membrane area. Both neuronal input resistance and the ratio of membrane time constant to input resistance were correlated with neuronal membrane area as measured anatomically. The relative electrical lengths of the different dendrites of individual neurones were investigated, by using simple transformations to take account of the differences in diameter and spine density between dendritic segments. A novel "morphotonic" transformation is described that represents the purely morphological component of electrotonic length. Morphotonic lengths can be converted into electrotonic lengths by division by a "morphoelectric factor" ([Rm/Ri]1/2). This procedure has the advantage of separating the steps involving anatomical and electrical parameters. These transformations indicated that the dendrites of the apical terminal arbor were much longer electrically than the basal or apical oblique dendrites. In relative electrical terms, most apical oblique trees arose extremely close to the soma, and terminated at similar distances to the basals. These results indicate that the dendrites of these pyramidal cells cannot be represented as single equivalent cylinders. The electrotonic lengths of the dendrites were calculated by using the electrical parameters specific membrane capacitance (Cm), intracellular resistivity (Ri), and specific membrane resistivity (Rm). Conventional values were assumed for Cm (1.0 muFcm-2) and Ri (100 omega cm), but three different Rm values were used for each cell. Two of these were within the conventionally accepted range (10,000-20,000 omega cm2), while the third value was an order of magnitude higher, in line with some recent evidence from modeling and whole-cell recording studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Surface Complexation of Calcium Minerals in Aqueous Solution.

The complexation of Alizarin Red S (ARS) at the surface of hydrous fluorite particles has been investigated by means of potentiometric titrations, adsorption experiments, and zeta-potential measurements in 0.1 mol dm(-3) KCl ionic medium at 25.0 degrees C, as well as by UV/visible specular reflectance, FT-IR, and FT-Raman spectroscopy. Chemical reaction models describing the equilibria of ARS (HA(2-)) at the aqueous fluorite surfaces ( identical withX) have been established as follows: Experimental data were evaluated using the computer program FITEQL on the basis of a constant capacitance model for the electric double layer. Surface complexation mechanisms involving the R-SO(3)(-), R-beta-OH, and R-alpha-OH active groups of the ARS molecule are proposed to describe coordination to the fluorite surface. Copyright 2000 Academic Press.

Journal Article↗
PubMed1998

Methodologies in the study of cell-cell fusion.

The process of membrane fusion has been profitably studied by fusing cells that express fusion proteins on their surfaces to the membranes of target cells. Primary methods for monitoring the occurrence of fusion between cells are measurement of formation of heterokaryons, measurement of activation of reporter genes, measurement of transfer of lipidic and aqueous fluorescent dyes, and electrophysiological recording of fusion pores. Fluorescence and electrical methods have been well developed for fusion of a nucleated cell expressing viral fusion proteins to red blood cell targets. These techniques are now being extended to the study of fusion between two nucleated cells. Microscopic observation of spread of fluorescent dyes from one cell to another is a sensitive and convenient means of detecting fusion on the level of single events. In such studies, both the membrane and the aqueous continuities that occur as a result of fusion can be measured in the same experiment. By following spread of aqueous dyes of different sizes from one cell to another, the growth of a fusion pore can also be followed. By labeling cells with fluorescent probes, a state of hemifusion can be identified if probes in outer membrane leaflets transfer but probes in inner leaflets or aqueous spaces do not. Electrical measurements-both capacitance and double-whole-cell voltage-clamp techniques-are the most sensitive methods yet developed for detecting the formation of pores and for quantifying their growth. These powerful single-event methodologies should be directly applicable to further advances in expressing nonviral fusion proteins on cell surfaces.

Cell Fusion↗
PubMed2004

Electric field-induced changes in lipids investigated by modulated excitation FTIR spectroscopy.

The effect of electric fields on dry oriented multibilayers of dimyristoylphosphatidylcholine (DMPC) was investigated by transmission Fourier transform infrared electric field modulated excitation (E-ME) spectroscopy. A periodic rectangular electric potential (0-150 V, 1.25 Hz, 28.4 degrees C +/- 0.2 degrees C) was applied across the sample. To discriminate electric field-induced effects from possible temperature-induced effects resulting from a current flow (<1 pA) across the sample, corresponding temperature-modulated excitation (T-ME) measurements within the temperature uncertainty limits of +/-0.2 degrees C at 28.4 degrees C were performed. T-ME induced reversible gauche defects in the hydrocarbon chains, whereas E-ME resulted in reversible compression of dry DMPC bilayers. Periodic variation of the tilt angle of the hydrocarbon chains is suggested. The degree of absorbance modulation in the CH-stretching region was found to be in the order of 1:700, corresponding to a variation of the bilayer thickness of Deltaz = 0.0054 nm. Using a series connection of capacitors as equivalent circuit of the cell resulted in E = (1.2 +/- 0.7) x 10(7) V/m for the electric field in DMPC. Young's elasticity modulus of DMPC could be calculated to be E( perpendicular ) = 2.2 x 10(6) Pa +/- 1.8 x 10(6) Pa, which is in good agreement with published data obtained by electric field-dependent capacitance measurements.

Dimyristoylphosphatidylcholine↗
PubMed2004

Ionic wave propagation along actin filaments.

We investigate the conditions enabling actin filaments to act as electrical transmission lines for ion flows along their lengths. We propose a model in which each actin monomer is an electric element with a capacitive, inductive, and resistive property due to the molecular structure of the actin filament and viscosity of the solution. Based on Kirchhoff's laws taken in the continuum limit, a nonlinear partial differential equation is derived for the propagation of ionic waves. We solve this equation in two different regimes. In the first, the maximum propagation velocity wave is found in terms of Jacobi elliptic functions. In the general case, we analyze the equation in terms of Fisher-Kolmogoroff modes with both localized and extended wave characteristics. We propose a new signaling mechanism in the cell, especially in neurons.

Actin Cytoskeleton↗
PubMed2001

In-column pyrolysis: a new approach to an old problem.

High-molecular-weight fragments produced during pyrolysis of both natural and synthetic materials often carry the most significant structural information. Their diagnostic value is usually limited when using commercial pyrolysis devices because of analyte discrimination on transfer from the pyrolysis unit to the GC column. A device enabling pyrolysis in line with GC column was developed to overcome this problem. Pyrolysis is carried out in a segment of deactivated stainless steel tubing. One end of the tubing is connected through a restrictor to a standard GC injector, and the other end is connected to a precolumn followed by a GC column. Pyrolysis is carried out by passing a pulse of electric current from a capacitive discharge power supply through the tubing. Nondiscriminated alkane pattern up to C-58 (limited by the temperature limit of the GC stationary phase) was observed for the pyrolysis of polyethylene. A comparison of conventional pyrolysis with in-column pyrolysis indicates that the range of semivolatile pyrolysis products that can be detected in the pyrograms extends much further toward higher-boiling compounds for the technique proposed. The new approach has also proved very useful in methodical variations of pyrolysis, including thermochemolysis using tetramethylammonium hydroxide.

Journal Article↗
PubMed1979

[Motility of the rumen after feeding sheep pelleted rations].

In an experiment with wethers the effect of the feeding with pelleted feed rations and the partial replacement of coarse fodder by non-treated beech sawdust on the motorial activity of the rumen was observed. The rumen motility was measured through a rumen fistula by means of the balloon method with the help of a capacitator primary unit, an electric manometer and a recording instrument. Over a period of 24 weeks the animals consumed 1.3 kg dry matter per day. It consisted of 41.8% meadow hay, 25.3% barley, 15.4% sawdust, 15.0% molasses, 1.3% urea, 0.76% mixed minerals and 0.48% hexametaphosphate in the form of pellets (test group) or the traditional classical form (control group). The feeding of pellets diminished the frequency (P less than 0.001) and the intensity of rumen contractions before and 1, 3 and 5 hours after feeding. Maximal frequency values were registered one hour after the food intake. During this time the number of secondary contractions of the rumen increased; differences of the frequency were, however, not registered, which means that the different physical form of the diet had no influence on the motorial activity of the rumen and that the food intake as such is the decisive factor. The diminished rumen motility in further hours after feeding was effected by treating the feed (grinding and pelleting).

Animal Feed↗
PubMed2004

Dynamics of transpiration, sap flow and use of stored water in tropical forest canopy trees.

In large trees, the daily onset of transpiration causes water to be withdrawn from internal storage compartments, resulting in lags between changes in transpiration and sap flow at the base of the tree. We measured time courses of sap flow, hydraulic resistance, plant water potential and stomatal resistance in co-occurring tropical forest canopy trees with trunk diameters ranging from 0.34-0.98 m, to determine how total daily water use and daily reliance on stored water scaled with size. We also examined the effects of scale and tree hydraulic properties on apparent time constants for changes in transpiration and water flow in response to fluctuating environmental variables. Time constants for water movement were estimated from whole-tree hydraulic resistance (R) and capacitance (C) using an electric circuit analogy, and from rates of change in water movement through intact trees. Total daily water use and reliance on stored water were strongly correlated with trunk diameter, independent of species. Although total daily withdrawal of water from internal storage increased with tree size, its relative contribution to the daily water budget (approximately 10%) remained constant. Net withdrawal of water from storage ceased when upper branch water potential corresponded to the sapwood water potential (Psi(sw)) at which further withdrawal of water from sapwood would have caused Psi(sw) to decline precipitously. Stomatal coordination of vapor and liquid phase resistances played a key role in limiting stored water use to a nearly constant fraction of total daily water use. Time constants for changes in transpiration, estimated as the product of whole- tree R and C, were similar among individuals (~0.53 h), indicating that R and C co-varied with tree size in an inverse manner. Similarly, time constants estimated from rates of change in crown and basal sap flux were nearly identical among individuals and therefore independent of tree size and species.

Panama↗