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Biomedical subjects

R Pethig

Publications and source records attributed to R Pethig.

At least 37 records · Page 2Linked to original sources
PubMed1993

Membrane changes accompanying the induced differentiation of Friend murine erythroleukemia cells studied by dielectrophoresis.

Dielectrophoresis measurements obtained using an image processing technique are reported over the frequency range 1 Hz to 100 kHz for the Friend murine erythroleukemia cell lines DS19 and R1 before and after treatment with hexamethylene bisacetamide and dimethylsulfoxide, agents that induce terminal differentiation in DS19 but not in R1 cells. Data are analyzed according to the single shell dielectric model of the cell. The membrane capacitance was found to fall by 30% and membrane conductivity by a factor of at least 5 when DS19 cells were induced to differentiate. R1 cells showed no such response. While the theoretical model was found to be useful for comparing differences in data for the different cell lines, several significant discrepancies between its predictions and the experimental data were observed, including positive dielectrophoretic collection at frequencies below 20 Hz and a smaller than predicted response to the membrane permeabilizing agents saponin and valinomycin. Factors that may have accounted for these discrepancies include surface charge effecgs, conduction parallel to the plasma membrane surface, and intracellular compartments.

Cell Differentiation↗
PubMed1992

Differences in the AC electrodynamics of viable and non-viable yeast cells determined through combined dielectrophoresis and electrorotation studies.

An electrode system is described for the near-simultaneous application and measurement of translational, levitational and rotational forces induced by AC electric fields, and this has been used to investigate the differences in the AC electrodynamics of viable and non-viable yeast cells. A new approach to the theoretical modelling of the experimental data has enabled these differences to be quantified in terms of changes in the conductivity of the cytoplasmic membrane and cell interior. The results are considered to have potentially important biomedical and biotechnological applications.

Cell Survival↗
PubMed1991

Dielectric-based biosensors.

A basic background is given of the concepts and measurements of dielectric phenomena, and two examples of dielectric-based biosensors are described. The way in which the dielectric properties of immobilized urease can be used to monitor the hydrolysis of urea is first outlined, while the second example describes how the phenomenon of dielectrophoresis can be used to monitor the concentration and viability of suspensions of cells or micro-organisms.

Animals↗
PubMed1990

Dielectrophoretic characterisation of Friend murine erythroleukaemic cells as a measure of induced differentiation.

Dielectrophoresis measurements, the study of the motion of particles in non-uniform a.c. electrical fields, have been made on three cell lines (DS19, R1 and DR1) of Friend murine erythroleukaemia cells as a function of hexamethylene bisacetamide (HMBA) treatment. The effects of saponin treatment on R1 cells and neuraminidase on human red blood cells were also studied. It is shown that the dielectrophoretic behaviour can be interpreted in terms of cell surface charge and cell membrane conductivity effects. HMBA reduces the cell surface charge on all three cell lines, and in lines DS19 and DR10, where the cells are induced to differentiate, there is an increase in effective cell conductivity. This gain in conductivity is concluded to be associated with either an enhanced lateral electrophoretic motion of delocalised ions or of the polarisability of dipoles at the membrane surface.

Acetamides↗
PubMed1989

On the dissociation constants of BAPTA-type calcium buffers.

We have determined or redetermined the calcium dissociation constants of seven BAPTA-type buffers with KD's in the range from 0.4 microM to about 20 mM in 300 mM KCl. These include four newly synthesized ones: 5-nitro BAPTA; 5,5'-dinitro BAPTA; 5-methyl-5'-nitro BAPTA; and 5-methyl-5'-formyl BAPTA. Moreover, we tabulate dissociation constants or KD's for BAPTA and eleven BAPTA-type buffers, compare most of them with an empirical curve based upon so-called Hammett values, and predict KD's for several still unsynthesized but potentially valuable buffers.

Buffers↗
PubMed1988

Applications of a new optical technique for measuring the dielectrophoretic behaviour of micro-organisms.

It is shown that the dielectrophoretic behaviour (motion in non-uniform a.c. electric fields) of micro-organisms can conveniently and reproducibly be measured by monitoring the decrease in optical absorbance of a cell suspension as the cells are collected at a micro-electrode array. The dielectrophoretic behaviour, as a function of the frequency of the applied electric field and conductivity of the supporting solution, can be determined more quantitatively and rapidly than by methods so far described in the literature. Results are presented for Micrococcus lysodeikticus, Bacillus subtilis and Escherichia coli for the frequency range 20 Hz to 4 MHz and theoretical considerations are presented for the effect of solution conductivity. A value of 0.2 S/m has been derived for the effective conductivity of M. lysodeikticus.

Bacillus subtilis↗
PubMed1988

Low-frequency dielectric properties of lysozyme as a function of hydration and pH of lyophilisation.

Dielectric measurements have been made on lysozyme-compressed powders as a function of hydration and of the pH at which the samples were lyophilised. A dielectric dispersion previously described in the literature and known as the alpha-dispersion is found to be strongly influenced by the lyophilisation pH, and reaches a maximum magnitude at around pH 11. A dielectric loss of the form of the alpha-dispersion is observed in polylysine hydrobromide and the sodium salt of polyglutamic acid, but not for polyglycine. These results can be understood in terms of proton transfer between the ionisable side-groups, as well as by the controlling influence of counter-ions in moderating the energetics of the proton transfer processes. Another, weaker and hitherto unreported, dielectric loss process has been found for lysozyme, polyglycine, polylysine and poly(glutamic acid). This is referred to as the alpha 2-dispersion and its characteristics can be understood in terms of vibrational motions of the polypeptide backbones and the plasticising action of bound water.

Electrochemistry↗
PubMed1987

Changes in cell surface charge and transmembrane potential accompanying neoplastic transformation of rat kidney cells.

Free flow electrophoresis measurements have been used to determine the surface charge density of normal rat kidney (NRK) cells and a clone of NRK, designated as 6m2, that exhibit a transformed phenotype at 33 degrees C and a non-transformed phenotype at 39 degrees C. A clone of 6m2, designated 54-5A4, which is transformed at both 33 degrees C and 39 degrees C was also studied. A surface charge density of -1.42 microC/cm2 was obtained for the NRK and non-transformed 6m2 cells at 39 degrees C, whereas at 33 degrees C values of -1.85 and -1.78 microC/cm2 were determined for the transformed 6m2 and 54-5A4 cells, respectively. It was found that 72% of the increased charge that appeared on the transformed 6m2 cells compared with the non-transformed 6m2 cells was RNAase sensitive. The time-dependent decrease in surface charge that accompanied the shift of the 6m2 cells from their transformed to non-transformed state was found to mirror the increase in transmembrane potential previously reported using a fluorescent dye technique, and was also comparable to the reported temporal changes in their morphology and virally-coded protein content.

Animals↗
PubMed1987

Electron spin resonance studies of the interaction of oxidoreductases with 2,6-dimethoxy-p-quinone and semiquinone.

Previous electron spin resonance studies have demonstrated that the decay of ascorbyl plus semiquinone radicals, produced in an aqueous mixture of ascorbate and 2,6-dimethoxy-p-quinone, is accelerated by ascites cells. This effect was concluded to involve a sulfhydryl-containing NAD(P)H-enzyme, and work on cultured cell lines showed that on neoplastic transformation the activity against the radicals was increased. We show here that at least three disulfide-oxidoreductases are able to quench the radicals in a similar way to that of viable cells. Glutathione reductase (EC 1.6.4.2) in the presence of NADPH and oxidised glutathione, and dihydrolipoamide dehydrogenase (EC 1.8.1.4) with NADH and lipoamide, are found to accelerate the radical decay by reducing the quinone or semiquinone. DT-diaphorase (EC 1.6.99.2) in the presence of NAD(P)H can also achieve this by reducing the quinone directly. Lipoamide dehydrogenase and glutathione reductase are also capable of reducing nitroxide spin labels, a finding considered of relevance to the reported reduction of such spin labels by neuroblastoma cells.

Animals↗
PubMed1987

Dielectric properties of body tissues.

A review is given of the dielectric properties of various mammalian tissues and biological fluids for the frequency range from 1 Hz to 10 GHz. The properties considered are the frequency variations of the relative permittivity and electrical conductivity. An attempt has been made to present data which can be considered to be the most typical for each material. The dielectric properties of aqueous solutions of amino-acids, polypeptides, proteins, and then cells, are first outlined in order to lay the groundwork for the understanding of the properties of tissues. The electrical characteristics of various tissues and blood are presented in tabular and graphical form, and the differences between normal and cancerous tissue is also discussed. The effects of necrosis and temperature changes are described and the important contribution that water makes to the overall properties is emphasised. An insight into some of the dominant physiological and biophysical processes responsible for the dielectric properties of biological materials is also attempted, since this should aid further developments of both the diagnostic and therapeutic applications of radiofrequency and microwave radiation. Such information is also relevant to an understanding of the possible biological hazards of such radiation. The ways in which dielectric studies can aid an understanding at the molecular level of the basic physiological differences between normal and cancerous tissue, as well as of the physico-chemical state of biological water, are also described.

Animals↗
PubMed1986

Surface charge measurements on Micrococcus lysodeikticus and the catalytic implications for lysozyme.

Electrophoresis measurements on Micrococcus lysodeikticus have shown that the net surface charge density on the cell wall is constant at around -1.5 microC/cm2 for the pH range 4-8. This result has enabled a quantitative analysis to be made of how the electrostatic field associated with the negatively charged cell wall influences the ionic strength and pH dependency of the lytic activity of lysozyme towards M. lysodeikticus. A dominant effect is the creation of a local pH gradient at the cell wall, and at high ionic strengths the lytic activity is found to be controlled by an electrostatic force of attraction between the lysozyme molecule and the cell wall. As the ionic strength of the supporting electrolyte is decreased, however, an electrostatic force of repulsion becomes dominant and is associated with a negative charge carried by the lysozyme molecule, which could possibly be the ionized Asp-52 residue at the active site. This is considered to arise from the fact that at low ionic strengths the fine details of the heterogeneous charge distribution on the cell wall and lysozyme molecule are only partially screened by counter ions.

Chemical Phenomena↗
PubMed1985

Dielectric studies of protein hydration and hydration-induced flexibility.

Dielectric measurements, as a function of hydration, are reported for collagen, cytochrome-c, elastin and lysozyme powders. The hydration dependence of the dispersion that occurs in the frequency range between 10 kHz and 10 GHz has been used to identify two classes of protein-bound water molecules (namely, rotationally hindered or unhindered), as well as the hydration level for the onset of an increasing protein flexibility. Such studies can aid an understanding of the relationship between enzyme activity and structural flexibility, and of hydration-induced changes in the structure and dynamics of protein structures.

Collagen↗
PubMed1985

Enzyme-controlled scavenging of ascorbyl and 2,6-dimethoxy-semiquinone free radicals in Ehrlich ascites tumor cells.

The rate of scavenging by Ehrlich ascites cells of anionic ascorbyl and 2,6-dimethoxy-p-semiquinone free radicals has been investigated by electron spin resonance spectroscopy both for viable cells and for subcellular fractions obtained by differential centrifugation. The scavenging activity is concluded to be associated with an NAD(P)H enzyme containing an active sulfhydryl group. Attempts to identify the enzyme with the reported properties of either semi-dehydro-ascorbate reductase or DT-diaphorase have not been successful. The overall free-radical scavenging activity for viable cells is dextrose dependent and is controlled by the coulombic barrier associated with the cell-surface charge. The cytotoxicity of the mixture of ascorbic acid with 2,6-dimethoxy-p-benzoquinone is concluded to result from a loss of NAD(P)H reducing power in the cells.

Animals↗
PubMed1984

Interaction of the 2,6-dimethoxysemiquinone and ascorbyl free radicals with Ehrlich ascites cells: a probe of cell-surface charge.

The rate of quenching by Ehrlich ascites cells of anionic 2,6-dimethoxy-p-semiquinone and ascorbyl free radicals is investigated as a function of cell concentration, the blocking of cell-surface sulfhydryl groups by N-ethylmaleimide, and the reduction of cell-surface charge by neuraminidase. The rate of quenching is found to be proportional to cell viability and to the number of free cell-surface sulfhydryl groups. The enzymatic action of neuraminidase results in an increase of the free radical quenching rate, indicating that this rate can be used as a probe of cell-surface charge. Measurements as a function of the ionic strength of the suspending electrolyte gave a value of -1.22 microC X cm-2 for the charge density at the ascites cell surface. This is equivalent to a surface membrane potential of -14 mV for a 150 mM NaCl electrolyte and is a value in good agreement with published electrophoresis data.

Animals↗