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L V Chernomordik

Publications and source records attributed to L V Chernomordik.

50 records · Page 3Linked to original sources
PubMed1987

The electrical breakdown of cell and lipid membranes: the similarity of phenomenologies.

The current responses of human erythrocyte and L-cell membranes being subject to rectangular voltage pulses of 150-700 mV amplitude and 5 X 10(-3)-10 s duration were recorded by means of the patch-clamp method. The behaviour of planar lipid bilayer membranes of oxidized cholesterol and UO2(2+)-modified bilayers of azolectin in a high electric field was investigated for comparison. The gradual growth in the conductance (reversible electrical breakdown) was found for both the cell membranes and lipid bilayers of the compositions studied, with the application of voltage pulses of sufficient duration, to be completed by its drastic enhancement (irreversible breakdown). The time interval preceding the irreversible breakdown and the rate of increase in conductance during the reversible breakdown are determined by the amplitude of the voltage applied. The recovery of the initial properties of the membrane following the reversible breakdown consists of the two stages, the latter substantially differing by their characteristic times. The first very rapid stage (tau much less than 1 ms) reflects the lowering of the conductance of small pores with decreasing voltage across the membrane. The diminishing of the number and mean radii of the pores resulting in their complete disappearance occurs only at the second stage of membrane healing, which lasts several seconds or even minutes. The phenomenological similarity of the cell and lipid membrane breakdown indicates that pores developed during the electrical breakdown of biological membranes arise in their lipid matrices. The structure and the properties of the pores are discussed.

Animals↗
PubMedDate not supplied

Structural intermediates in influenza haemagglutinin-mediated fusion.

Fusion pore formation in the haemagglutinin (HA)-mediated fusion is a culmination of a multistep process, which involves low-pH triggered refolding of HA and rearrangement of membrane lipid bilayers. This rearrangement was arrested or slowed down by either altering lipid composition of the membranes, or lowering the density of HA, and/or temperature. The results suggest that fusion starts with the lateral assembly of activated HA into multimeric complexes surrounding future fusion sites. The next fusion stage involves hemifusion, i.e. merger of only contacting membrane monolayers. Lysophosphatidylcholine reversibly arrests fusion prior to this hemifusion stage. In the normal fusion pathway, hemifusion is transient and is not accompanied by any measurable transfer of lipid probes between the membranes. A temperature of 4 degrees C stabilizes this 'restricted hemifusion' intermediate. The restriction of lipid flow through the restricted hemifusion site is HA-dependent and can be released by partial cleaving of low pH-forms of HA with mild proteinase K treatment. Lipid effects indicate that fusion proceeds through two different lipid-involving intermediates, which are characterized by two opposite curvatures of the lipid monolayer. Hemifusion involves formation of a stalk, a local bent connection between the outer membrane monolayers. Fusion pore formation apparently involves bending of the inner membrane monolayers, which come together in hemifusion. To couple low pH-induced refolding of HA with lipid rearrangements, it is proposed that the extension of the alpha-helical coiled coil of HA pulls fusion peptides inserted into the HA-expressing membrane and locally bends the membrane into a saddle-like shape. Elastic energy drives self-assembly of these HA-containing membrane elements into a ring-like complex and causes the bulging of the host membrane into a dimple growing towards the target membrane. Bending stresses in the lipidic top of the dimple facilitate membrane fusion.

Endopeptidase K↗
PubMedDate not supplied

[Reversible electrical breakdown of cholesterol-containing lipid bilayer membranes modified with holothurin A].

Reversible electrical breakdown of cholesterol-containing BLM modified with holothurin A, i. e. a significant reversible increase of membrane conductivity under the effect of the electrical field was described. So when the voltage approximately 0.3 V was applied to the BLM for 10 ms its conductivity was reversibly increased by 4 orders as compared to the initial one. Reproducibility of current oscillograms, non-linear current breakdown--potential relationship and non-linear spasmodic decrease of conductivity at step-like reduction of the potential on the membrane show similarity of this phenomenon with the reversible breakdown of the membranes of oxidized cholesterol and of asolectin BLM in the presence of UO22+ ions. The mechanism of reversible electrical breakdown of BLM is discussed in terms of the development of a great number of local conductive defects in the membrane under the effect of the electrical field.

Cholesterol↗
PubMedDate not supplied

[Effect of exposure to "stress" on the electrical properties of BLM].

The influence of high potential and hydrostatic pressure gradients on BLM has been studied. It has been found that short exposures of BLM to the above factors, which are nearly as strong as those rupturing BLM, often induce in the membrane unusual states characterized by drastic increase in the current fluctuations with simultaneous increase of its average value. The level of fluctuations and the average current on individual membranes subjected to intermittent exposures vary appreciably. Of greatest interest are the membranes for which the average current value is not much higher than the background level. Such membranes can fluctuate steadily for several hours without any appreciable change in their behavior. In these cases the minimum current value during fluctuations often corresponds to the background current. Usually the current fluctuations on membranes excited by potential or hydrostatic pressure gradients cease abruptly. The electrical properties of such membranes are virtually the same as those of the unstressed membranes. The qualitative studies of the influence of the solution composition and temperature showed that in the range 25--40 degrees C in different solutions the excitation effects of BLM from general lipids of brain and a lecithin-cholesterol mixture are qualitatively similar and resemble those due to some biologically active substances diminishing the mechanical stability of BLM. Some possible mechanisms of excitation of BLM exposed to stress factors are discussed.

Biophysical Phenomena↗
PubMedDate not supplied

[Liposome fusion with planar lipid membranes].

Potentiodynamic method was used for investigating bilayer lipid membrane (BLM)- liposomes (LS) interaction. BLM was formed from egg lecithin and its mixture with phosphatidylserine (PS); LS-from PS. It is shown that in the presence of calcium in the aqueous phase (1-10 mM) and charged phospholipids in both LS and BLM, fusion of LS with BLM is observed. The fusion event was registered by measuring the increase of negative charge density on BLM surface opposite to that facing the LS.

Calcium↗
PubMedDate not supplied

[Potentiodynamic method of studying the reaction between liposomes and bilayer lipid membranes].

Changes of surface potential difference of neutral BLM in the presence of negatively charged liposomes were controlled by means of potentiodynamic method. The liposomes were prepared by sonication of PS-suspension in buffer solution. BLM was formed conventionally from lecithin--decane mixture. Measurements were carried out in buffer solution 2 mM KCL, 5 mM Tris-Cl pH 7.6) at 30 degrees C. It is shown that the liposomes are irreversibly bound to BLM, but do not fuse with it under the conditions investigated.

Alkanes↗
PubMedDate not supplied

[Cation selectivity of a BLM in a state of "stress"].

In asymmetric conditions (by electrolyte concentration) cyclic voltage current curves of BLM were measured in a stress state initiated after a short -- time effect of a strong electric field. BLM from negatively charged lipids were shown to exhibit notable cation -- anion selectivity under these conditions. The result obtained agrees with the assumption to the effect that stress and preclamping fluctuations are related to the formation of through pores the inner face of which is lined with the polar heads of lipids.

Electric Conductivity↗