1,720,983 research outputs found
D-glucose-induced alterations in the electrical parameters of human erythrocyte cell membrane
No full textThe alterations of the passive electrical parameters (the permittivity epsilon and the electrical conductivity sigma) of human erythrocyte cell membrane induced by the presence of glucose in the extracellular medium have been investigated by means of dielectric spectroscopy measurements. The membrane permittivity epsilon(s) and the permittivity epsilon(p) and electrical conductivity sigma(p) of the cytosol have been evaluated on the basis of a recent analytical model proposed by Prodan et al., 1983 1161, that takes into account the whole dielectric spectrum of a cell suspension, consisting of both the low-frequency a-dispersion and the high-frequency beta-dispersion. Our results show a marked increase of the membrane permittivity epsilon(s) close to a glucose concentration of 20 mM. On the contrary, the electrical properties of the cytosol do not change appreciably. This finding strengthens the hypothesis that glucose interactions involve primarily the cell membrane and the mechanism of the transport is briefly discussed. (c) 2009 Elsevier B.V. All rights reserved
Effect of the shape of human erythrocytes on the evaluation of the passive electrical parameters of the cell membrane
No full textOn the dielectric relaxation of biological cell suspensions: the effect of the membrane electrical conductivity
No full textPolarizability of spherical biological cells in the presence of localized surface charge distributions at the membrane interfaces
No full textThe electrical polarizability alpha(omega) of a biological cell in the presence of a layer of localized, partially bounded, charges at the two cell membrane interfaces has been calculated within the dipolar approximation. The cell is modeled in the light of the single-shell spherical model, but the results can be easily extended to shelled particles of more complex shape. Under the influence of an external electric field, the presence of these charge distributions, which added to the ones originated by the mismatch of the complex dielectric constants of the different media, produces a further dielectric relaxation, besides the one due to the usual Maxwell-Wagner effect. We explicitly find the contribution that must be added to the electrical polarizability alpha(omega) in order to take into account the surface electrical currents originated by the localized charges free to move on the membrane surfaces. Our results, maintaining their validity whatsoever the values of the surface charge distributions and, moreover, whatsoever the values of the membrane conductivity are, extend the applicability of the model recently proposed by Prodan et al. [Biophys. J. 95, 4174 (2008)], who developed an analytical solution which offers reliable results only in the case of weak surface charge distributions and, moreover, for negligible small values of the membrane conductivity. Our approach, removing these constrains, represents a valuable improvement toward more realistic biological cell models and widens the use of dielectric relaxation methods to a larger class of biological systems
Effect of polymer adsorption on PEO-coated latex particles during salt-induced aggregation
No full textThe salt-induced aggregation of polystyrene particles in dilute aqueous solutions has been studied by means of dynamic light scattering measurements and the hydrodynamic radius of the resulting aggregates has been evaluated during the time evolution of the whole process. Poly(ethylene oxide) (PEO) polymer adsorbed on the particle surface at different amounts has been used to modify the inter-particle interactions resulting in the formation of clusters of increasing size or in the stabilization of the suspension, depending on the polymer molecular weight. The aggregation regime, i.e. a diffusion limited cluster aggregation (DLCA) occurring in the polymer-free latex suspension, is partially modified according to the polymer percentage adsorbed on the particle surface. At high polymer content, the polystyrene latex undergoes a complete steric stabilization. The deviation from a DLCA regime has been observed for different polymer contents and for polymers of different molecular weights, from 1.5 to 2000 kD. The alterations of the aggregation rates, induced by the polymer interactions, are presented and briefly discussed. (C) 1999 Elsevier Science B.V. All rights reserved
Numerical simulation of dielectric spectra of aqueous suspensions of non-spheroidal differently shaped biological cells
No full textDielectric properties of biological cells in the dipolar approximation for the single-shell ellipsoidal model: the effect of localized surface charge distribution at the membrane interface
No full textThe dielectric behavior on non-spherical biological cell suspensions: an analytic approach
No full textAbstractThe influence of the cell shape on the dielectric and conductometric properties of biological cell suspensions has been investigated from a theoretical point of view presenting an analytical solution of the electrostatic problem in the case of prolate and oblate spheroidal geometries. The model, which extends to spheroidal geometries the approach developed by other researchers in the case of a spherical geometry, takes explicitly into account the charge distributions at the cell membrane interfaces. The presence of these charge distributions, which govern the trans-membrane potential ΔV, produces composite dielectric spectra with two contiguous relaxation processes, known as the α-dispersion and the β-dispersion. By using this approach, we present a series of dielectric spectra for different values of the different electrical parameters (the permittivity ɛ and the electrical conductivity σ, together with the surface conductivity γ due to the surface charge distribution) that define the whole behavior of the system. In particular, we analyze the interplay between the parameters governing the α-dispersion and those influencing the β-dispersion. Even if these relaxation processes generally occur in well-separated frequency ranges, it is worth noting that, for certain values of the membrane conductivity, the high-frequency dispersion attributed to the Maxwell-Wagner effect is influenced not only by the bulk electrical parameters of the different adjacent media, but also by the surface conductivity at the two membrane interfaces
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