The Structural-Functional Damage of Fibrinogen Oxidized by Hydrogen Peroxide.

The effect of peroxide-induced oxidation of fibrinogen on modification of its primary structure and functional properties was investigated. The oxidation sites were shown to be Met, Trp, and His residues. Using the DLS method, it was found that the oxidative modification of fibrinogen results in the change of microrheological characteristics of fibrin network. The fibrinogen oxidation diminishes its tolerance to plasmin hydrolysis and deteriorates the factor XIIIa ability to stabilize the fibrin gel.

[Effect of lipopolysaccharide O-side chains on the adhesiveness of Yersinia pseudotuberculosis to J774 macrophages as revealed by optical trap].

A method has been developed for the quantitative estimation of the binding force of a model microsphere with a eukaryocyte based on the optical trap in order to study the molecular mechanism of adhesion between an individual bacterium and a host cell. The substantial role of LPS O-side chains in the adhesiveness of Yersinia pseudotuberculosis 1b to J774 macrophages has been revealed with the use of a set of microspheres functionalized with lipopolysaccharide (LPS) preparations and antibodies with different specificities. The results indicate the significance of the O-antigen as a pathogenicity factor of Y. pseudotuberculosis in colonization of a macroorganism. The developed methodical approaches can be applied to the study of molecular mechanisms of the pathogenesis of pseudotuberculosis and other infectious diseases to improve antiepidemic service.

Transient dielectro-deformations of erythrocyte governed by time variation of cell ionic state.

The possibility is shown to monitor the transient ionic state and volume of erythrocyte suspended in low ionic strength solution (LISS) by registration of the dielectro-deformation (DD) of a cell. The adequate theoretical basis is developed. Possible registration modes are considered analytically and numerically using the theory of dielectro-deformation of erythrocytes developed previously.

Dielectro-deformations of erythrocyte: analysis of the ellipsoidal shear model.

Using the theoretical analysis within the framework of the proposed ellipsoidal shear electromechanical model of erythrocyte, the main mechanisms and relationships have been established and studied for the deformations of erythrocytes caused by a spatially homogeneous high-frequency electric field. The main types of the stress-strain curves characteristic of stationary and dynamic deformations caused by the rectangular-pulse and harmonic modulations of the field amplitude have been calculated. The relationship has been established between the parameters of essentially nonlinear stress-strain curves and mechanical, electric, and geometric parameters of erythrocyte. The impossibility of unlimited elongation of erythrocyte by the field, due to the conservation of the cell volume and surface area, has been shown, and the dependence of the maximum possible elongation of the cell on its volume has been calculated. It has been shown that the relaxation time of dynamic deformations of erythrocyte in the presence of an electric field considerably differs from that characteristic of the membrane material and sharply decreases with the increase of the initial elongation of the cell.

Stationary deformations of erythrocytes by high-frequency electric field.

The theory of erythrocyte deformation by high-frequency (HF) electric field, based on ellipsoidal approximation for cell shape, is developed. Various possible deformational regimes of cell elongation by the field are analyzed, depending on the relation between the bending and the shear deformations of cell membrane and the magnitudes of corresponding mechanical stresses arising. The role of mechanical, electrical, and geometrical parameters of erythrocyte in formation of various parts of deformational curves (cell length-field strength) is elucidated, including the initial part and the geometrical saturation region. The measurements of the stationary elongation curves of erythrocytes by Krueger and Thom [Biophys. J. 73 (1997) 2653] are analyzed quantitatively. The shape of the measured curves is described exactly by the theory for the whole range of field strengths and temperatures used. The temperature-dependent values of erythrocyte volume and cytoplasmic conductivity are obtained from this description in the range (- 15-25 degrees C).

Spontaneous and forced oscillations of cell membrane of normal human erythrocytes: absence of resonance frequencies in a range of 0.03-500 Hz.

The spectra of natural oscillations of human erythrocyte cell membranes were studied experimentally and theoretically. The measurements were carried out at room temperature for both single normal cells and erythrocyte rouleaux in a range of 0.03-500 Hz. The spectra were measured at a resolution better than 1% using two techniques: registration of spontaneous membrane oscillations induced by thermal agitation in the surrounding medium and registration of the amplitude-frequency characteristics of the forced oscillations of erythrocyte elongation induced by a high-frequency electric field with the amplitude harmonic modulation. The spectra measured by both techniques had no resonance frequencies and decreased monotonically with the frequency increase. These results are confirmed by the theory developed for the extracellular excitation mechanisms of membrane oscillations. The spectra of active oscillatory biomechanical processes were measured for comparison. These processes are ciliary beating of human bronchial epithelium and ciliary beating and artificial periodic contractions of the cytoplasm of the ciliate Spirostomum ambiguum. The quality of the resonance lines of the order of 10-20 registered may serve as estimates for the line width in search of the resonance oscillations in erythrocytes induced by active cell processes.

Optical Diagnostics of Mechanical Properties of Red Blood Cells based on the Deformation by High Frequency Electric Field.

Erythrocyte placed in a low-conductivity isotonic medium can be elongated by a high frequency electric field. The elongation can be registered optically, finally enabling the determination or monitoring of elastic moduli and viscous properties of erythrocytes. However, an unambiguous evaluation of mechanical parameters from the optical data is complicated. It requires an adequate theory of dielectro deformation which takes into account the influence of the cell's mechanical, electric, and transient shape parameters on field-induced deformations. The present work is aimed at the development of a comprehensive and experimentally verified theoretical basis for the dielectro-deformational investigation of erythrocytes. The previous concept of the dielectro-deformation process, supported solely by the shear deformation of erythrocyte membrane, is revised completely. It is shown that in the practical relevant range of dielectro deformation, it is mainly supported by bending deformation of the membrane, with a gradual development of shear deformation as the cell becomes more elongated. This new bending-shear theory of dielectro deformation is developed here. The theory is shown to describe unambiguously both observational and quantitative data on the static and dynamic dielectro deformation of erythrocytes. © 1999 Society of Photo-Optical Instrumentation Engineers.