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Biomedical subjects

D Lerche

Publications and source records attributed to D Lerche.

At least 73 records · Page 4Linked to original sources
PubMed1984

Electrostatic fixed charge distribution in the RBC-glycocalyx and their influence upon the total free interaction energy.

On the basis of a recently developed biophysical model of cell-cell interaction, including electrostatic, electrodynamic, steric and bonding/bridging interaction energies the influence of different fixed charge (dissociated groups of the glycocalyx) density distributions in red blood cell (RBC) glycocalyces on the total free interaction energy was investigated. An analytical equation of electrostatic free energy on the basis of the linear Poisson-Boltzmann approach taking into account arbitrary distributions of fixed glycocalyx charges was obtained and corresponding free electrostatic energies of three example distributions were calculated. The electrodynamic, steric and bonding/bridging energies were computed as usual. It was shown that the free energy as a function of interaction distances strongly depends on the charge distribution and, correspondingly, the "weight" of this energy term in the total free interaction energy balance equation. Generally, it can be stated that as more charges are assumed to be fixed in the outer layer of RBC glycocalyx as more important becomes the electrostatic energy in contrast to the remaining three terms.

Electricity↗
PubMed1984

[Importance of pH- and osmolarity-dependent changes in deformability- determining factors on the filterability of human erythrocytes].

The deformability of erythrocytes was characterized by measuring their filterability through cellulose filters under low pressure, their cellular geometry and elastic membrane properties. A decreased filterability of suspensions of washed erythrocytes with increasing pH (5.5-7.9) and osmolarity (220-510) was found. The influence of RBC-deformability determining factors on the measured quantity (relative time of filtration) was determined. It is concluded that the viscosity of the cell interior has a predominating influence on the filterability through cellulose filters among all experimentally changed factors determining the deformability. The influence of the cell volume on the filterability is small compared with that of secondary effects of volume changes (dilution or concentration of hemoglobin, changes of cell volume concentration at constant hematocrit). The influence on the erythrocyte volume increases with decreasing pore size.

Erythrocyte Membrane↗
PubMed1983

A biophysical model for interaction of cells with a surface coat (glycocalyx). I. Electrostatic interaction profile.

A model of the primary stage of cell-cell interaction is assumed, including not only the classical electrostatic and electrodynamic energies in the sense of DLVO theory but also steric interaction energy, the energy of specific and non-specific bonds and the energy due to changes of surface potential. Furthermore, in this paper, we exploit recent advances in the understanding of the structure of the cell surface (glycocalyx), assuming the fixed electrostatic charges (dissociated groups of the glycocalyx), to be space charge densities and the glycocalyx itself to be an adsorption layer. In this first part the profile of the electrostatic potential between two cells is calculated on the basis of the linear Poisson-Boltzmann equation (analytical integration) and discussed in dependence on charge densities of the glycocalyx, the separation distance between cells and the ionic strength of the suspension medium.

Biophysical Phenomena↗
PubMed1983

[Characterization of the effect of retransfusion of UV-irradiated autologous blood--synoptic examination of clinical, metabolic, rheologic and hemodynamic results in patients with arterial occlusive disease].

In 6 inpatients with angiographically ascertained arterial obstructive disease the influence of the retransfusion of uv-radiated own blood on metabolic, haemorheological, clinical and haemodynamic parameters was examined. In 4 patients a pseudoradiation was performed as control. The results confirm that under the ultra-violet radiation changes develop in the sense of a normalisation of the parameters examined. Here an improved walking capacity is accompanied by an improvement of the O2- and substrate utilisation of the tissue and the flowing properties. On the basis of the results the improvement of the microcirculation under ultra-violet radiation is to be derived. The sites of action of the ultra-violet radiation are shown in the causal chain in arterial obstructive diseases and partial steps of the mode of action are described.

Arterial Occlusive Diseases↗
PubMed1983

Mechanical membrane properties of human red blood cells and their change due to metabolic disturbance.

Blood of patients suffering from non-spherocytic chronic haemolytic anemia due to individual mutations of glucose-6-phosphate-dehydrogenase (G-6-PD) and pyruvate kinase (PK) was investigated by biochemical and rheological methods. Both enzymopathies are characterized by a strong increase (by the factor 2 to 4) in the overall RBC-rigidity and the elastic membrane shear modulus of the RBC. There was a positive correlation between the changed elastic shear modulus and the clinical picture in the case of PK deficiency and, in contrast, a negative correlation for patients with G-6-PD enzymopathies. The ability of RBC to change their shape or the static deformability is determined by the excess surface regarding to the enclosed volume, by the rheological properties of the hemoglobin content and by the membrane extension and bending moduli. The dynamic deformability is characterized by the time constant for rapid elastic and plastic deformations and becomes important for entrance and discharge processes in the microcirculation. These rheological relevant properties are subjected to metabolic control. Although for both enzymopathies the mechanism of hemolysis is not understood in detail, it has to be assumed that PK deficient RBC are mostly phagocytized and on the other hand G-6-PD deficient cells are destroyed to a higher extent by intravasal hemolysis. The aim of this study was to investigate whether or not expected changes in the RBC membrane structure due to the decreased ATP production by PK enzymopathies and diminished NADPH production by G-6-PD deficiencies result in abnormal mechanical membrane properties. The answer should give a better understanding of the premature RBC destruction.

Anemia, Hemolytic↗
PubMed1982

[Experimental studies on the rheologic behavior of blood in ultraviolet therapy].

The increased apparent blood viscosity proved in peripheral circulatory disease, the frequent failure of therapy by means of vasodilating medicaments and the successful therapy with the help of ultraviolet radiation of blood (UVB) by means of various techniques motivated investigations of the flow properties of blood with UVB. In six patients with angiologically ascertained arterial occlusive disease the flow properties of blood were investigated under standardized conditions by both viscosimetric techniques and independent of it by means of the centrifugation method. Plasma viscosity, apparent blood viscosity, parameters of aggregation and deformation of erythrocytes were determined before and after fictitious UVB on the hand one and before and after real UVB on the other hand. It was shown that within the limit of measurement accuracy there were no significant differences between fictitious and real UVB in plasma viscosities. Both the aggregation parameter of the centrifugation method and the apparent blood viscosity for low shear gradients before the 3rd UVB and all following ones differed significantly from those of the first UVB. No changes were found in the deformation parameters HCC infinity and the apparent viscosity for high shear gradients during UVB therapy. Possible mechanisms leading to the demonstrated improvements of the flow properties of blood by means of UVB are discussed.

Arterial Occlusive Diseases↗
PubMed1982

Spontaneous aggregation of washed human erythrocytes in isotonic media of reduced ionic strength. Conclusions about the spatial arrangement of the N-terminal part of the glycophorins.

Aggregation measurements of washed human erythrocytes (RBC) were made in an NaCl-PBS solution under laminar shear conditions. An artificial aggregation was caused by decreased pH and reduced ionic strength and characterized by collision efficiency, i. e. the probability of permanent aggregate formation. It was found that aggregation increases with reduced ionic strength and decreased pH value of the medium. Aggregation can be inhibited by addition of human serum albumin and neuraminidase treatment (removal of sialic acids). As calculations show, the results cannot be explained by the force balance between electrostatic repulsion and attraction due to dispersion forces. It was assumed that this type of aggregation involves reversible changes of the surface structure of RBC. Possible conclusions for the arrangement of the glycophorins of the glycocalyx (surface coat) are discussed.

Erythrocyte Aggregation↗
PubMed1981

Scanning electron microscopical characterization of La3+- and concanavalin A-induced aggregations of untreated and neuraminidase-treated human erythrocytes.

The aggregates of washed control and NANAse-treated human red blood cells (RBC) were characterized by scanning electron microscopy (SEM). Aggregation of RBC was performed under well-defined laminar shear conditions (78.6 S-1) in a horizontally arranged coaxial cylinder system. Generally, with increasing La3+ concentration in the PBS the aggregates became larger and the contact between the RBC "more intensive". This was evidenced by more cells per aggregate, an enlargement of contact areas, a change of cell shape in the contact region and signs of fusion phenomena. Especially at high La3+ concentrations on the cell surface of treated and untreated RBC some deposits were seen by SEM which are possibly La3+- phosphate precipitates. Neuraminidase treatment promoted the described La3+ effects. Concanavalin A-induced RBC agglutinates were different from the more spherical former ones and showed a network-like morphology. The conclusions drawn on the basis of light and scanning electron microscopical investigations are confirmed by quantitative values of an aggregation index estimated in parallel.

Cell Aggregation↗
PubMed1980

Investigations of artificial aggregation of washed human erythrocytes caused by decreased pH and reduced ionic strength.

Aggregation measurements of washed human erythrocytes were carried out in a NaCl-PBS solution under laminar shear conditions. An artificial aggregation was caused by decreased pH and reduced ionic strength, and characterized by the collision efficiency, e.m., the probability of a permanent aggregate formation. It was found that the aggregation increases reducing the ionic strength and decreasing the pH of the medium. Pretreatment with Amphothericin B did not change the aggregation. The results cannot be explained neither by the usual D.L.O.V. theory (force balance between electrostatic repulsion and attraction due to dispersion forces) nor by direct influence of the changed transmembrane potential. It is supposed that this type of aggregation involves reversible changes of the membrane and/or the surface structure.

Amphotericin B↗
PubMed1976

Temporal and local concentration changes in diffusion layers at cellulose membranes due to concentration differences between the solutions on both sides of the membrane.

By means of a laser-interferometrical method diffusion layers at the interface of a noncharged cellulose membrane are studied. These layers are induced by a concentration difference between the NaCl solutions separated by the membrane. The temporal and local shift of the NaCl concentration in the diffusion layers were measured. A steady-state concentration profile could be obtained for times of 121 sec less than or equal to to less than or equal to 484 sec. The concentration profiles at any time (to less than or equal to 900) are not a linear function of the membrane surface, but could be fitted to a quadratic function. The thickness of the diffusion layers is also a function of time and its stationary value in this system is (575 +/- 49) X 10(-6)m. The role of concentration polarization for the determination of phenomenological thermodynamic coefficients of membranes is discussed and a new method is suggested, which excludes the difficulties of the concentration polarization in the diffusion layers at the membrane.

Cellulose↗