Search PubMed⌕ Search

Biomedical subjects

A Bonincontro

Publications and source records attributed to A Bonincontro.

At least 37 records · Page 2Linked to original sources
PubMed1991

Radiofrequency dielectric spectroscopy of ribosome suspensions.

Dielectric measurements on different ribosome suspensions were carried out in the frequency range from 10 kHz to 1 GHz. In intact ribosomes two dispersions were detected: one around 100 kHz and the other one in the MHz region. In separated ribosomal subunits and in ribosomes resuspended in a buffer with no magnesium ions (relaxed ribosomes) only the MHz dispersion was observed. Electrical conductivities of the samples at 1 kHz were also measured. The temperature dependence of the two dispersions was investigated and a tentative attribution was proposed.

Electric Conductivity↗
PubMed1991

Temperature dependence of DNA dielectric dispersion at radiofrequency.

We have studied the dielectric behavior of DNA aqueous solutions at various ionic strengths and in the presence of the specific DNA ligand ethidium bromide, in the frequency range 1 MHz-1 GHz, at different temperatures ranging from 5 to 40 degrees C. The activation enthalpies of the dielectric relaxations studied were obtained by Arrhenius plots of In(tau T)-1 vs. T-1. The results are consistent with a counterion fluctuation model as previously developed by Mandel and colleagues.

DNA↗
PubMed1991

Non-linear dependence of the dielectric properties of chick embryo myoblast membranes exposed to a sinusoidal 50 Hz magnetic field.

Primary chick embryo myoblasts can be a useful tool for studying the developmental events which accompany myoblast differentiation, particularly myoblast membrane fusion. To determine whether the electrical properties and/or fusion in these systems are affected by 50 Hz magnetic fields, chick embryo myoblast cultures were exposed to B-field intensities ranging from 1 to 10 mT. The electrical parameters of the myoblasts, i.e. membrane conductivity, membrane permittivity and the conductivity of the cell interior (cytosol) were determined by the analysis of conductivity dispersion data in the radio frequency range (10 kHz-100 MHz). Preliminary results indicate that the time of fusion (60 h) is not affected by these fields, but that the absolute values of the two membrane electrical parameters are affected. In particular, a B-field intensity-dependent decrease was observed. The maximum effect resulted after a 1 h exposure to a magnetic flux density of about 5 mT. The conductivity of the cytosol remained unchanged. These data seem to indicate that exposure to 50 Hz magnetic fields affects both static and dynamic membrane properties in primary chick embryo myoblasts.

Animals↗
PubMed1990

Dose-dependent effects of ionizing radiation on in vitro myoblast fusion.

We have recently demonstrated by dielectric relaxation studies in the radio-frequency range that there is a sharp decrease in the conductivity and permittivity of the membranes of chick embryo myoblasts in vitro at the time of fusion (60 h) (Bonincontro et al. 1987). This sharp fall in membrane electrical parameters was subsequently shown to be due to changes in ionic flux, particularly of the Na+/K+ equilibrium (Santini et al. 1988). Ionizing radiation induces a wide variety of effects on biological membranes, including variations in membrane ionic transport. We wished to investigate if sublethal doses of gamma-irradiation could affect membrane electrical parameters and thus myoblast membrane fusion. Consequently, chick embryo myoblast aggregate cultures were irradiated with 3.25, 5.15 or 6.35 Gy at 24 h of culture. We found that the lower dose delays membrane fusion by about 10 h while the two higher doses block fusion up to 120 h of culture. Aggregates showed a very high cell viability. The possible mechanisms by which ionizing radiation causes these variations in myoblast membrane electrical properties and fusion are discussed.

Animals↗
PubMed1989

Rescue of the Li+-induced delay of embryonic myogenesis in vitro by added inositol.

Signaling between embryonic myoblasts to coordinate gene expression is part of normal skeletal muscle development in the embryo. An unanswered question is the nature of the second messengers carrying the information to the nucleus. We have investigated the cell membrane events associated with the binding of prostaglandin to a transient receptor on the embryonic chick myoblast membrane in vitro. The membrane events include a transient change in membrane order seen by electron paramagnetic resonance (EPR), a change in cell-cell adhesion, a rapid decrease in membrane permeability and fusion of the membrane bilayers. The addition of 20 mM Li+, an inhibitor of inositol phosphate phosphatase, perturbed the transient change in membrane order and delayed the change in cell-cell adhesion and conductivity for 2-6 h. Other alkali metal ions had no such effects. The addition of inositol to the culture medium in the continued presence of Li+ restored the normal timing of the two latter events. We interpret this as evidence for an inositol phosphate second messenger system which might connect the activation of the prostaglandin receptor with the change in cell-cell adhesion, the changes in membrane conductivity and perhaps bilayer fusion. We suggest that Li+, by blocking the regeneration of polyphosphatidylinositol from inositol phosphate, reduced the efficiency of the second messenger system such that further differentiation of the myoblast membrane was delayed. The exogenous inositol provided an alternative source and membrane differentiation was unaffected.

Animals↗
PubMed1989

Complex dielectric constant of arginine-DNA and protamine-DNA aqueous systems at 10 GHz.

The complex dielectric constant of arginine and protamine from herring sperm (clupeine) and their complexes with herring sperm DNA was measured at 10 GHz in the temperature range -20 to +45 degrees C by a microwave cavity perturbation method. The experimental results were analysed in terms of a three-component equation (solute molecules, interfacial water and bulk water) to calculate the fractional volume of modified water and hence the specific hydration of the samples. A fourfold reduction of the specific hydration is observed for the clupeine molecule as compared to the free monomers. This is consistent with a folded conformation of the protein in solution. The specific hydration of the complex between clupeine and DNA is reduced by 50% with respect to the weighted average for the uncomplexed components. This result indicates an intimate contact between clupeine and DNA with exclusion of water molecules and is consistent with the highly condensed form of nucleoprotamines which is known in vivo.

Animals↗
PubMed1988

Cesium ions delay membrane fusion of chick embryo myoblasts in vitro: a conductivity study.

Cesium has a wide range of effects on biological systems. However, the effects of this ion on muscle differentiation are not known. We have recently demonstrated that there is a sharp decrease in the conductivity and permittivity of the membranes of chick embryo myoblasts at the time of fusion (Bonincontro, A., Cametti, C., Hausman, R.E., Indovina, P.L. and Santini, M.T. (1987) Biochim. Biophys. Acta 903, 89-95). Analysis of the conductivity dispersion data in the radiowave frequency range using a 'single-shell' model showed that individual myoblasts and unfused myoballs have significantly higher membrane conductivity and membrane permittivity than fused myoballs. We show here that the sharp fall in these membrane electrical parameters occurs at 60 h of culture and is indeed very abrupt, taking place within one hour. In addition, we also demonstrate that cesium ions delay the sharp decrease in both the conductivity and permittivity of myoblast membranes by about 30 h. We discuss the possible mechanisms by which cesium perturbs potassium transport across these membranes and how this perturbation may affect fusion itself.

Animals↗
PubMed1988

Influence of hyperthermia, pH and culturing conditions on the electrical parameters of Chinese hamster V79 cells.

Conductivity measurements in the frequency range 10 kHz-100 MHz have been performed on Chinese hamster fibroblasts V79 exposed to hyperthermia in different experimental conditions. The membrane electrical conductivity is decreased when cells are heated for 1 h at 44 degrees C or 3 h at 43 degrees C at pH 7.25. This effect has not been observed on cell samples following heating for 1 h at 43 degrees C at pH 7.25. However, if the pH of the culture medium is adjusted to 6.50 or 6.0 before hyperthermic exposure, a substantial decrease of membrane conductivity is observed. In cells maintained in partially spent medium before heating, a 3 h treatment at 43 degrees C at pH 7.25 does not produce any effect on membrane conductivity. The results of all these experiments seem to indicate that some alteration of the energy-driven mechanisms involved in active transport across the plasma membranes may be responsible for the observed effects.

Animals↗
PubMed1987

Changes in myoblast membrane electrical properties during cell-cell adhesion and fusion in vitro.

Characteristic of the process of myogenesis are the changes in the composition and organization of the cell membrane. While poorly understood, these changes have biochemical and biophysical relevance. Recently, changes in molecular order of the myoblast membrane which accompany differentiation in vitro have been observed (Santini, M.T., Indovina, P.L. and Hausman, R.E. (1987) Biochim. Biophys. Acta 896, 19-25). To further investigate these cell fusion processes we have examined additional physical parameters: conductivity and permittivity of the myoblast membrane during differentiation which reflect the molecular arrangement of the membrane. The determination of these parameters is possible because in the radio frequency range suspensions of cells in an electrolyte buffer show a characteristic conductivity dispersion due to the interfacial polarization. An analysis of our experimental data based on a 'single-shell' model showed that conductivity and permittivity of the membrane of pre- and post-fusion myoblasts varied significantly and abruptly. The conductivity of the cell interior (cytosol) remained constant. We discuss the significance of the observed changes in these membrane parameters for myogenesis.

Animals↗
PubMed1987

Hydration properties of DNA-lysine gels by microwave dielectric measurements as a function of temperature.

Dielectric measurements by a cavity perturbation method at 10 GHz in the temperature range from -20 degrees C to +45 degrees C are reported for aqueous gels of herring sperm DNA in the presence of 1 or 3 lysine molecules per nucleotide. Measurements for lysine-water and DNA-water systems are also reported. The experimental results can be accounted for by the presence of interfacial water, with dielectric properties different from those of bulk water, and are analyzed in terms of a three component equation (solute molecules, interfacial water and bulk water) to calculate hydration parameters of the systems. The lysine molecule is found to coordinate a particular number of water molecules, in agreement with the literature. The specific hydration of DNA is reduced by the presence of lysine, indicating a direct interaction between the polyion and the aminoacid: a decrease to about 50% was observed at a ratio of one molecule of lysine per nucleotide. A suggestion is made that the interaction is mainly electrostatic in nature.

DNA↗
PubMed1987

Effect of gamma irradiation on membranes of normal and pathological erythrocytes (beta-thalassemia).

The influence of ionizing radiation on the membrane of human normal erythrocytes has extensively been studied and a variety of effects including changes in the cation fluxes [3, 9] or in non-electrolytes permeability [5, 6, 11], in membrane fluidity, in peroxidation of unsaturated lipids as well as chemical composition or structural modifications [4, 7, 8] has been observed. However, only few studies deal with the effects of ionizing radiation on pathological red blood cells. In this work, we have investigated by means of electron spin resonance (ESR) spectroscopy the effects of 60Co gamma-radiation on the normal and homozygous beta-thalassemic human erythrocyte membranes [12, 13].

Cell Membrane Permeability↗
PubMed1987

Alteration of membrane conductivity and fluidity in human erythrocyte membranes and erythrocyte ghosts following gamma-irradiation.

Alterations of electrical properties of human erythrocyte membranes induced by gamma irradiation have been studied by means of conductivity measurements in the frequency range from 10 KHz to 100 MHz. The results clearly demonstrate the role played by haemoglobin in the structural modification of the membrane produced by gamma irradiation. Further support for this point of view has been derived from electron spin resonance measurements carried out on the same samples, labelled with different spin labels which probe the outer half layer of membrane at different penetration levels.

Cobalt Radioisotopes↗
PubMed1984

Effect of ions on counterion fluctuation in low-molecular weight DNA dielectric dispersions.

The dielectric permittivity of aqueous solutions of low-molecular weight DNA (Mr = 3.2 X 10(5) ) in the presence of MgCl2 and AgNO3 has been measured in the frequency range from 5 kHz to 30 MHz, at a temperature of 25 degrees C. The DNA concentration was 3.5 X 10(-4) M in terms of phosphate and the salt concentration was varied from 1 X 10(-5) to 2 X 10(-4) M. The dielectric results have been analyzed in terms of two contiguous dielectric dispersions, and characteristic parameters have been discussed on the basis of polyelectrolyte theories which deal with counterion fluctuation. Some molecular parameters of the DNA molecule in electrolyte solutions are estimated.

Animals↗