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V S Markin

Publications and source records attributed to V S Markin.

At least 55 records · Page 3Linked to original sources
PubMed1984

A theory of osmotic lysis of lipid vesicles.

Osmotic lysis of vesicles is shown to begin when the membrane expansion due to osmotic pressure exceeds its critical value, delta S, at which a membrane ruptures to form a pore. The dependence of delta S on the vesicle radius and respective osmotic pressures are obtained. It is found that osmotic pressure necessary for small (100 A) vesicles to rupture should exceed 30 atm, for large (10 000 A) vesicles it being as small as 10(-3) atm. In the case of large (greater than or approximately 1000 A) vesicles the value of relative expansion of the membrane at which its rupture occurs in a reasonable time only depends slightly on the vesicle radius. For instance, for 10 000 A vesicles it amounts to 3%. The tension of membrane rupture is about 8 dyn/cm for large vesicles. Membrane tension, although it decreases considerably as a result of rupture and pore formation, does not vanish completely. It supports the residual intravesicular pressure causing the efflux of vesicle (cell) contents. Simultaneously, osmotic influx of water through the membrane occurs that results in either complete rupture of the membrane with the efflux of the whole of the contents, or its gradual washout in either of two, quasi-steady or pulse-wise regimes. In the first case a pore is steadily open, whereas in the second case it alternately opens and closes, ejecting about 5% of internal solution each time. Lysis kinetics is analyzed. Pulse-wise regime of lysis is shown to be the most likely one.

Erythrocytes↗
PubMed1984

On the theory of membrane fusion. The stalk mechanism.

Based on literary data, conditions necessary for membrane fusion are discussed. It is proposed that fusion mechanisms should be classified according to the primary act involving a change in the membrane structure. Two principal fusion mechanisms are identified: the stalk mechanism, starting with the appearance of a stalk between approaching membranes, and the adhesion mechanism which involves bilayer reorganization as a result of a tight junction of the membranes. The origin and evolution of the monolayer and bilayer stalks between membranes are analysed. Using the expression for the elastic energy of the stalk it was possible to find the value of the spontaneous curvature of its membrane, Ks, at which the existence of a stalk is in principle possible. It is shown that, within the framework of the stalk mechanism, there exists a possibility of either the formation of a stalk of a finite radius, or complete fusion. The Ks values have been determined at which one of the variants occur. The energy barrier of the hydrophobic interaction and the elastic energy barrier, which have to be overcome by the membranes to form the stalk are analysed. The theoretical analysis of the stalk formation mechanism is supported by experimental data. It has been shown by freeze-fracture electron microscopy that the addition of Ca+2, Mg+2, Mn+2 or Cd+2 to suspensions of egg phosphatidylcholine and cardiolipin (1:1 or 3:1) leads to the formation of numerous intramembrane particles (imp's) and crater-like (stalk) structures.

Biophysical Phenomena↗
PubMed1984

On the theory of membrane fusion. The adhesion-condensation mechanism.

The primary act of the adhesion-condensation mechanism underlying membrane fusion is considered. This act involves the formation of a close dehydrated contact between membranes and the subsequent crystallization of molecules of the external monolayers in the contact region. Crystallization associated with a decrease in the area per molecule gives rise to elastic stresses which cause a disruption of the external monolayer of the membrane in the contact region. This disruption results in the formation of a trilaminar structure (a monolayer fusion occurs). It has been shown that for the formation of a trilaminar structure between liposomes with a radius of 20 nm the contact area must be at least 22% of that external monolayer. Moreover, the membrane has to overcome an energy barriers; according to estimates for 20 nm liposomes, the maximum value of the barrier is approximately 20 kT. The height of the disruption barrier decreases with increasing area of the contact region. Estimates have been obtained for the minimum area of a "hole" in the contracting monolayers, which arises from their disruption for 20 nm liposomes, this area is approximately 2 X 10(2) nm2. The developed theory explains the data obtained by the Papahadjopoulos group in their experiments on the fusion of phosphatidylserine liposomes (Portis et al. 1979; Wilshut et al. 1980; Düzgünes et al. 1981); in addition, it enables the description of the mechanism underlying the disruption of a liposome as a result of expansion of its membrane. The process of disruption was studied by Kwok and Evans (1981).

Biophysical Phenomena↗
PubMed1981

Lateral organization of membranes and cell shapes.

The relations among membrane structure, mechanical properties, and cell shape have been investigated. The fluid mosaic membrane models used contains several components that move freely in the membrane plane. These components interact with each other and determine properties of the membrane such as curvature and elasticity. A free energy equation is postulated for such a multicomponent membrane and the condition of free energy minimum is used to obtain differential equations relating the distribution of membrane components and the local membrane curvature. The force that moves membrane components along the membrane in a variable curvature field is calculated. A change in the intramembrane interactions can bring about phase separation or particle clustering. This, in turn, may strongly affect the local curvature. The numerical solution of the set of equations for the two dimensional case allows determination of the cell shape and the component distribution along the membrane. The model has been applied to describe certain erythrocytes shape transformations.

Animals↗
PubMed1975

Nigericin-induced charge transfer across membranes.

The electric properties of the bilayer lecithin membranes have been studied in the presence of the antibiotic nigericin. When the antibiotic concentration is about 10(-7) ohm-1 cm-2. The potassium ion concentration gradient gives rise to a transmembrane potential of the order of 40 mV per 10-fold concentration gradient with the side of the higher potassium concentration negative. The transmembrane potential produced by the hydrogen ion concentration gradient is a function of the potassium ion concentration which is equal on both sides of the membrane. For low potassium ion concentrations the hydrogen potential has the expected polarity with the solution having higher concentration of protons negative. For potassium ion concentrations exceeding 0.03 M the hydrogen potential has the reverse polarity. This unexpected result cannot be accounted for in terms of the available simple hypotheses about the charge transport mechanism for nigericin in BLM. In order to account for the experimental results obtained, a theoretical approach has been developed based on the assumption that charge is transported across the membrane by nigericin dimers. The theoretical predicitons are in satisfactory agreement with the experimental results. The model also yields some predictions which may be verified in future experiments.

Anti-Bacterial Agents↗
PubMedDate not supplied

Electrostatic assay of phospholipase A activity: an application of the second harmonic method of monitoring membrane boundary potentials.

To evaluate phospholipase A activity a new assay is suggested. This assay is based on the recording of boundary potential changes of the planar bilayer lipid membrane during enzymatic hydrolysis of lipids. To register these changes, a second harmonic method is used. Sensitivity of the assay is about 0.0002 units/ml regardless of the impurities that may be present in the samples. One analysis takes about 5 min.

Electricity↗
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↗