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Biomedical subjects

V S Markin

Publications and source records attributed to V S Markin.

At least 73 records · Page 4Linked to original sources
PubMedDate not supplied

[Rate of excitation propagation in a reduced Hodgkins-Huxley model. I. Rapid relaxation of the sodium current].

The question of calculating excitation propagation velocity is analyzed on the basis of the Hodgkin-Huxley model. The activation of the sodium current is assumed to be rapid as compared to the rate of potential variation. Because of slow variation of potassium activation and sodium inactivation the dynamics of these processes is assumed to be of negligible effect in the region of impulse velocity formation. By means of pieace-wise linear approximation of thus obtained voltage-current characteristics the characteristics the analytical solution of the problem was found. In two limiting cases this solution coincides with the solutions of Kolmogorov and Scott. The dependence of impulse velocity on parameters is analyzed and illustrated graphically.

Models, Neurological↗
PubMedDate not supplied

[Rate of excitation propagation in a reduced Hodgkins-Huxley model. II. Slow relaxation of the sodium current].

The influence of sodium current activation on the value of nerve excitation conduction velocity is investigated on the basis of Hodgkin-Huxley model. The potassium activation and sodium inactivation are considered as slow processes which do not develop to an appreciable extent in the region of conduction velocity formation. The system of equations was derived and solved analytically after neglecting the dependency of sodium relaxation time on potential; the approximation of steady-state sodium activation was also used with the help of Hevyside function. The algebraic equation for conduction velocity was obtained; its solution has a simple analytical form in two limits of rapid and slow sodium current relaxation. The comparison with the experimental data has shown that at not very high temperatures the slow (compared to the potential dynamics) sodium current relaxation approximation is more appropriate. The dependency of impulse velocity on capacitance and conductance of the fiber was analyzed.

Electrophysiology↗
PubMedDate not supplied

[Comparison of discrete models of charge transfer in thin membranes. I. Stationary regime].

The model of the ion transport through thin membranes is discussed. It is assumed that there exist some steps of the ion transfer in the membrane volume. Theory of absolute rate of processes is used to derive an equation for stationary transmembrane flow. As a result the thory parameters are connected with the form of potential energy curve of permeable ions into the membrane phase.

Electric Conductivity↗
PubMedDate not supplied

[Rate of excitation propagation in a reduced Hodgkins-Huxley model. III. Integrodifferential equations].

The Hodgkin - Huxley system of equations is reduced to single integral-differential equation in neglection of slow variables dynamics. Two limiting cases of fast and slow sodium activation processes are considered. The first case leads to a nonlinear differential equation for the potential, the second one - to an ordinary differential equation with a known source as a function of coordinate. Such a simplification is due to approximation of steady-state sodium activation variable with the help of Heviside function. The validity of this approximation is discussed; the corresponding error is estimated by calculation of the second approximation for the source function.

Mathematics↗
PubMedDate not supplied

[Comparison of jumping and electrodiffusion mechanisms of particle movement in thin membranes. I. Statement of the problem. Stationary transfer].

The communication presented is the first in the cycle on comparative analysis of hopping (three barrier) and electrodiffusion description of particle movement in thin membranes. A case of stationary transfer is considered. It is shown that the three barrier hopping description is adequate to the electrodiffusion one when the membrane is non-uniform with a high narrow barrier in the middle. The uniform electrodiffusion description is adequate to the three barrier one only in the cases when the limiting stage is presented by the transfer through a membrane surface or the border of small outer electric fields.

Biological Transport↗
PubMedDate not supplied

[New poly-(3-hydroxybutyrate)-based systems for controlled release of dipyridamole and indomethacin].

New poly-(3-hydroxybutyrate)-based systems for controlled release of anti-inflammatory and antithrombogenic drugs have been studied. The release occurs via two mechanisms (diffusion and degradation) operating simultaneously. Dipyridamole and indomethacin diffusion processes determine the rate of the release at the early stages of the contact of the system with the environment (the first 6-8 days). The coefficient of the release diffusion of a drug depends on its nature, the thickness of the poly-(3-hydroxybutyrate) films containing the drug, the concentrations of dipyridamole and indomethacin, and the molecular weight of the poly-(3-hydroxybutyrate). The results obtained are critical for developing systems of release of diverse drugs, thus, enabling the attainment of the requisite physiological effects on tissues and organs of humans.

Azotobacter↗
PubMedDate not supplied

[Mechanosensitivity of gramicidin A channels in semispherical bilayer membranes at constant tension].

Mechanoelectrical transduction in gramicidin A channels was studied in macroscopic planar lipid bilayer membranes bulged at constant tension. We found a supralinear increase in the single channel activity, which was proportional to the square of membrane radius but could not be accounted for by the increase in membrane surface area or by recruitment of new channels. When being extrapolated to biological membranes, these observations may suggest that the activity of permeability of ion channels can be influenced simply by changing the shape of the membrane, with or without stretching.

Biomechanical Phenomena↗