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Biomedical subjects

V V Malev

Publications and source records attributed to V V Malev.

36 records · Page 2Linked to original sources
PubMed1980

[Isotope permeability of bilayer phospholipid membranes].

The paper considers the electrically silent transport of ions across bilayer membranes formed from the bulk ox brain lipids with the addition of cholesterol to the molar ratio 1 : 2. Fluxes of Rb, K, Cs, Na, Cl, measured by the tracer technique, are compared with those calculated from membrane conductivity determined simultaneously. The tracer permeability coefficients of membranes (P) proved to be greater than permeability coefficients predicted from membrane conductance. The data obtained show that P does not depend on salt concentration (in the range from 2.10(-3) to 1 M) in adjacent solutions and ion species. The results reveal no correlation between the electrical conductivity of the membranes and P. Neither do the tracer fluxes depend on the transmembrane of the membranes protenial up to 150 mB. Experimental findings and theoretical considerations lead to the conclusion that the ions studied cross the membrane in the form of ionic pairs originating inside the membrane close to the interface. The entrance of ions into the membrane phase appeared to be the limiting step of the process.

Animals↗
PubMed1979

[Effect of gramicidin on the potassium conductance of an isolated frog muscle fiber].

The antibiotic gramicidin A (1.10(-6) M) increases the K+ conductance of normal and detubulated frog skeletal muscle fibres in isotonic K2SO4 solution to a steady-state level, which is reached in 6--9 min, and corresponds to 8058 +/- 1669 and 5767 +/- 902 Om-1. 10(-6)/cm2, resp. There is no correlation between the initial K+ conductance and the value of the steady state of gramicidin A-induced conductance (r = 0.24). According to the dimer hypothesis, the dissociation rate constant of the garmicidin channels was found to be 0.006 +/- 0.0001 sec-1. This result supports the suggestion of a higher stability of gramicidin channels in muscle compared to the bimolecular lipid membranes.

Animals↗
PubMed1978

[Transport of the substance through thin membranes with narrow pores after the preceding stage of surface diffusion].

A model of the substance transport through thin membranes is discussed. Existence of a step of the surface diffusion of permeable particles is assumed preceding its entrance into membrane channel. An expression is given for the stationary flow, which has earlier been obtained for other transport models. It is shown that the permeant affinity to the membrane surface is the main condition for the validity of the scheme in question.

Animals↗
PubMed1976

[Effect of valinomycin on the structure of water-lecithin liposomes].

It has been established that water--lecithin liposomes in the heptane phase are formed in the course of equilibration of lecithin solution in heptane with water phase containing Na, K-picrate. The salts penetrate both the water nucleus of liposomes and their lecithin shell. The addition of valinomycin to this system does not change the water content in liposomes, but considerably increases the salt absorbed by the lipid shell of liposomes. A characteristic S-shape curve showing the relation between picrate extraction and the valinomycin concentration might be explained as an indication of a cooperative change of the structure of lecithin shell. This phase transition is induced by one valinomycin molecule per 10(3)--10(4) lecithin molecules.

Liposomes↗
PubMedDate not supplied

[Comparison of discrete models of charge transfer in thin membranes. II. Nonstationary conditions, small polarizing voltages].

The multi-step model of charge transfer is used to describe the transient behaviour of the membrane system. Analysis is carried out for the membranes with non-homogenous narrow pores. If the degree of non-homogenity of pores is high, slow relaxation occurs. In general the parameters of this relaxation do not coincide with those derived by one-jump approach to ion transfer through thin membrane.

Biological Transport↗
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

[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

[Effect of temperature on the interaction of gramicidin A and its dimer analog with the muscle fiber membrane].

Potassium conductance of single muscle fibres from Rana esculenta was studied in isotonic K2SO4 solution under constant current conditions using double sucrose gap method. At room temperature the channel formation by gramicidin was much faster than that of the synthetic head to head covalently linked gramicidin dimer. The increase of temperature by 8-10 degrees C resulted in a considerable rise of both dimer- and gramicidin-induced conductances. The effect was much greater than in the case of bilayers indicating a remarkable entropy change in the muscle fibre membrane. The temperature dependence of adsorption was more pronounced than that of desorption: there was no effect on desorption of dimer and only 20% of the temperature-activated desorption of gramicidin irreversibly bound at room temperature.

Animals↗
PubMedDate not supplied

[Analysis of nerve fiber deformation during excitation].

A description of the potential--dependent strains of the nerve fiber is considered as a problem of finding the velocity and pressure distributions in two liquid volumes which are divided by a thin cylindric shell. The isotropic shell equations were used as the boundary conditions for this problem. The strain amplitude predicted is near to the observed one, but the strain dynamics in the model discussed does not coincide with the one recorded under the experimental conditions.

Animals↗
PubMedDate not supplied

[Gramicidin A-induced membrane conductance of isolated muscle fiber].

The conductance of single fibres from m. ileofibularis of Rana esculenta was studied in isotonic K2SO4 solution under constant--current conditions using the double sucrose gap method. The antibiotic gramicidin A effects a drastic increase of membrane conductance. Variation of the gramicidin-induced conductance with gramicidin concentration in the bathing solution (10(-8)-5,5 . 10(-7) M) was investigated. Gramicidin-induced conductance was proportional to the square of gramicidin concentration in the solution, as expected in a channel made of gramicidin dimer.

Animals↗
PubMedDate not supplied

[Kinetics of bilayer lipid membrane formation].

Methods of irreversible thermodynamics are used to describe some kinetic processes on lipid membranes (for example, growth of the black spots during bilayer formation, the spreading of shimming lens etc.). The equation derived here shows the balance of the membrane system energy. Although this equation is generally only a boundary condition for the corresponding hydrodynamic problem it could be directly applied for analysing the bilayer formation processes. The application of this theory to experimental results permitted a determination of the membrane viscosity, and this was found to be about 10 P for ox brain lipids.

Kinetics↗
PubMedDate not supplied

[Kinetics of lens formation on phospholipid membranes].

Kinetics of lens formation on phospholipid membranes of different thickness (50-5 nM) has been investigated. It has been shown that lenses on the "gray" membranes (approximately 50 nM) are stabilized when alternating voltage (100-500 mV) of high frequency is applied. Semiempiric equation is used for the description of the spreading of lenses. Addition of florizin to the adjacent water solutions leads to an appearance of the slow relaxation component of the lens base radius. The results obtained show that the swimming lens method may be utilized for the investigation of the slow interaction processes between the membrane and their modifiers.

Animals↗
PubMedDate not supplied

[Comparison of discrete models of charge transfer in thin membranes. III. Unstable conditions, large polarizing voltages].

The validity of one-jump approach to ion transfer through thin membranes is discussed. The detailed analysis is carried out for the transport scheme with slow conformational processes in the membrane volume. It is shown that there exists some difference between stationary and nonstationary values of the transfer coefficient. The second essential feature of this scheme is the appearance of a slight minimum on the relaxation curve with high voltages in the membrane system.

Biological Transport↗