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Results for “Lipid Bilayers”

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At least 91 records · Page 5Linked to original sources

PubMedDate not supplied

[Effect of a permanent magnetic field on the formation of lipid bilayers].

Effect of the constant magnetic field (MF) by the induction of 1.1 T on formation kinetics of bilayer lipid membranes (BLM) from egg lecithin in decane was discovered. Under the effect of MF oriented in parallel to the lipid film place the rate of BLM formation decreases, while at its perpendicular orientation it is accelerated. The stationary value of BLM capacity decreases under MF effect at both orientations. The discovered changes in the rate of BLM formation under MF effect seem to be related to the effect of MF on liquid crystalline structure of colour lipid film.

Electric Conductivity↗

PubMedDate not supplied

[Changes in the structure of lipid bilayer membranes in magnetic fields].

In terms of structural voluminous phases the structure of bilayer lipid membranes in the constant magnetic field far from the point of phase transition is examined. The field influence on the area of the membrane black part is due to surface tension of voluminous phases. It is noted that the effect is squared with the field and is negative under gomeotropic orientation of the molecules on the surface. The dependence of the effect on temperature is predicted and its possible mechanisms are examined.

Chemical Phenomena↗

PubMedDate not supplied

[Measurements of non-electrogenic fluxes through lipid bilayers induced by Men+/nH+-exchangers].

In the presence of concentration gradient of metal ions on bilayer lipid membrane (BLM) the addition of non-electrogenic carriers results in a formation of concentration gradient of hydrogen ions in the unstirred layers near membrane. Addition of protonophore under these conditions brings about the formation of diffusion potential of hydrogen ions. This effect underlies the method of measuring non-electrogenic fluxes on BLM initiated in the presence of Men+/nH+ - exchangers. The proposed method was tested on the following Men+/nH+ - exchangers: nigericin, monensin and A23187. The order of cationic selectivity of the given carriers obtained by measuring the potentials on BLM in the presence of protonophores agrees with literature data, which were obtained by direct measurements of ionic fluxes.

Cation Exchange Resins↗

PubMedDate not supplied

[Specific electric resistance of a narrow gap between two lipid bilayer membranes].

The study deals with measurements of specific electric resistance of a narrow gap between two bilayer lipid membranes (BLM). The technique is based upon the influence of the outer electric field on the distance between two BLM which has been revealed earlier. The curve of specific resistance/solution ionic strength obtained suggests that surface conductivity is significant in similar systems. In gaps narrower than 40 nm possible increase of water viscosity must be also taken into consideration. A hypothetic mechanism of electric connection between cells is proposed.

Electric Conductivity↗

PubMedDate not supplied

[Interaction of perfluoro-organic compounds with flat lipid bilayers].

It has been found that contact interaction between the drops of perfluoro-organic compounds (PFOC) and bilayer lipid membranes (BLM) results in the fusion of PFOC and BLM drops. In the process PFOC is incorporated into the lipid bi layer of BLM, which decreases the BLM stability.

Chemical Phenomena↗

PubMedDate not supplied

[Effect of pH on the properties of planar lipid bilayers of cholesterol and alpha-monolaurine].

It is discovered that pH of liquid electrolyte influences the structure, stability and conductance of bilayer lipid membranes (BLM) formed from cholesterol-alpha-monolaurine mixture in n-octane. The most stable BLM are formed at cholesterol-alpha-monolaurine weight ratio 1:1, BLM specific resistance being maximal and their thickness minimal (2.9 nm). A sharp reduction of BLM stability is noted when pH is deviated in acidic or alkaline medium. The obtained data are discussed from the viewpoint of adsorbed charge influence on the structure of BLM formed of uncharged lipids.

Alkanes↗

PubMedDate not supplied

[Effect of a binuclear rhenium complex on the conductivity of lipid bilayer membranes for alkali metal ions].

Conductivity of bilayered lipid membrane (BLM) for the ions of alkali metals under action of binuclear rhenium complex (V) [Re2(Ph3P)2 (AHK)2O3Cl4] has been analyzed. It is found that BLM conductivity sharply increases in presence of lithium ions, then it drops and slowly increases again up to maximum value which is not changed. If sodium, rubidium and caesium chlorides are used as electrolytes the BLM conductivity almost does not change. The mechanisms of change of BLM conductivity is suggested for the ions of alkali metals under interaction with binuclear complex of rhenium.

Cesium↗

PubMedDate not supplied

[Conductivity fluctuation of lipid bilayer membranes formed on a substrate].

In the range of voltages -0.9-(+)0.9 V the fluctuations of conductivity of bilayer lipid membranes formed on the support (s-BLM) were measured. The new cut of the wire from stainless steel SS-10T served as the support. The similarity of current fluctuations for s-BLM as well as for support-electrolyte interface was observed, some quantitative distinctions are revealed. Three types of fluctuations are observed; 1) large current jumps observed as current steps at DC channel; 2) small current fluctuations near zero line with the spectrum of 1/f alpha type (flicker noise); 3) short current jumps, whose amplitudes are many folds higher than mean noise level, and the density of distribution function falls off as fluctuation magnitude raised to power 2.5 for s-BLM.

Animals↗

PubMed1998

Binding of avidin modified antibody to biotinylated metal supported membranes and liposomes changes the physical properties of lipid bilayer.

Various methods have been applied to study the physical properties of metal supported bilayer lipid membranes (s-BLM) and large unilamellar liposomes containing biotinylated phospholipids during the binding of IgG modified by avidin. Electrostriction method applied to s-BLM showed that addition of avidin-IgG (A-IgG) complex in a small concentration (0.2 mumol/l) resulted in an approximately twofold decrease of membrane capacitance, C, increase of elasticity modulus in direction perpendicular to the membrane plane, E perpendicular, by 5-20%, increase in intrinsic membrane potential, delta phi m, by approximately 30 mV, and an approximately 5-15% increase of the coefficient of dynamic viscosity, eta. The method of ultrasonic velocimetry showed that addition into the suspension of liposomes of unmodified IgG did not induce any changes in ultrasound velocity, while addition of A-IgG complex in a concentration range of 0-1 mumol/l led to an increase of the velocity number [u]. The plot of changes of [u] versus A-IgG concentration has a tendency to saturate at concentrations above 0.5 mumol/l, which suggests long-range interactions in the membrane induced by strong binding of A-IgG to the biotin sites on the membrane. Probably, this binding leads to a decrease of the coefficient of adiabatic compressibility of liposomes.

Avidin↗

PubMed1981

Agonist-activated ionic channels in acetylcholine receptor reconstituted into planar lipid bilayers.

Planar lipid bilayers were formed with the mixed chain phospholipid 1-stearoyl-3-myristolglycero-2-phosphocholine. Acetylcholine receptor membrane fragments or the purified receptor protein was incorporated into these bilayers by fusing receptor-containing vesicles with the planar membranes a few degrees below the lipid phase transition temperature. Single-channel currents activated by nicotinic agonists in the reconstituted system resembled those observed in intact rat and frog muscle membrane as measured by the patch clamp technique. The observed channel characteristics did not depend on the degree of receptor purification. Thus, the receptor-enriched fragments and those depleted of nonreceptor peripheral peptides, the purified receptor monomer/dimer mixtures, and the isolated receptor monomer as defined by gel electrophoresis all shared similar electrochemical properties in the synthetic lipid bilayer. The agonist-activated ionic channel seems, therefore, to be contained within the receptor monomer.

Acetylcholine↗

PubMedDate not supplied

[Lipid oxidation in bilayer lipid membranes linked with the reaction of oxidation of NAD.H by atmospheric oxygen].

It is shown that along with NAD.H oxidation with air oxygen peroxide oxidation of lipids forming the membrane takes place in bilayer lipid membranes modified with ubiquinone. During nicotin amide oxidation proton absorption takes place. Peroxide oxidation of lipids results in the liberation of H+ ions, which in its turn brings about the formation of protone-deficient or enriched (against aqueous solution) layers adjacent to the membrane. The potential value on the membrane is shown to depend on nicotine amide and oxygen concentration, on ubiquinone presence and lipid composition of the membrane. It has been also indicated that the transmembrane potential difference is initiated with a sharp change of aqueous solution pH by 0.05--0.4 units.

Air↗

PubMed1988

Solvent history dependence of gramicidin A conformations in hydrated lipid bilayers.

Reconstituted lipid bilayers of dimyristoylphosphatidylcholine (DMPC) and gramicidin A' have been prepared by cosolubilizing gramicidin and DMPC in one of three organic solvent systems followed by vacuum drying and hydration. The conformational state of gramicidin as characterized by 23Na NMR, circular dichroism, and solid state 15N NMR is dependent upon the cosolubilizing solvent system. In particular, two conformational states are described; a state in which Na+ has minimal interactions with the polypeptide, referred to as a nonchannel state, and a state in which Na+ interacts very strongly with the polypeptide, referred to as the channel state. Both of these conformations are intimately associated with the hydrophobic core of the lipid bilayer. Furthermore, both of these states are stable in the bilayer at neutral pH and at a temperature above the bilayer phase transition temperature. These results with gramicidin suggest that the conformation of membrane proteins may be dictated by the conformation before membrane insertion and may be dependent upon the mechanism by which the insertion is accomplished.

Circular Dichroism↗

PubMedDate not supplied

[Characteristics of the generation of transmembrane current higher harmonics in lipid bilayers in glycerol and 1,2-propane diol solutions].

It is shown that structural rearrangements of bilayer lipid membrane induced by glycerol and 1,2-propane diol result in noncompensated second harmonic of transmembrane current having quadratic dependence on input voltage and a weak dependence on frequency. The third harmonic has cubic dependence on input voltage and decreases with an increase in frequency. The mechanism is discussed according to which generation of non-compensated second harmonic is due to the formation of the intermediate lipid phase with viscoelastic properties differing from the initial bilayer in the process of structural rearrangements. The presence of this phase conditions the possibility of appearance of noncompensated second harmonic.

Electricity↗

PubMedDate not supplied

[Inclusion of erythrocyte membranes into planar lipid bilayers].

Planar lipid bilayer membranes (PM) were modified by membrane vesicles prepared from rabbit erythrocytes. Vesicles contained amphotericin B and tetraethylammonium. Voltage-current relationships of modified PM were investigated. Semi-fusion, the inclusion of sealed vesicles into PM with formation of contact bilayer consisting of one lipid monolayer of the erythrocyte membrane and another monolayer of PM, was shown to appear some minutes after the contact of vesicles with PM. Some tens of minutes later fusion of the erythrocyte membranes with PM was observed. Fusion occurred either by opening out of vesicles or by incorporation of sealed vesicles into PM. The temperature rise increased the fusion probability. Sealed vesicles were incorporated in PM asymmetrically: the contact area was always smaller than the noncontact vesicle surface.

Amphotericin B↗

PubMed2002

Electrical capacitance of lipid bilayer membranes of hydrogenated egg lecithin at the temperature phase transition.

Electrical capacitance of the planar bilayer lipid membrane (BLM) formed from hydrogenated egg lecithin (HEL) has been studied during many passages through the phase transition temperature. In contrast to the BLM from individual synthetic phospholipids, membranes from HEL did not demonstrate any capacitance change at the phase transition temperature maximum, as measured by differential scanning calorimeter at 52 degrees C. Instead, two temperatures have been discerned by capacitance records: thickening at 42-43 degrees C and thinning at 57-59 degrees C. The first temperature region is close to the transition temperature of dipalmitoyllecithin, whereas the second is close to that of distearoyllecithin, two main components of the HEL. It was suggested that capacitance measurements were able to reveal a phase separation in the BLM from HEL which was not detected by differential scanning calorimetry. The phase transition of the BLM from the liquid crystal state to the gel state is followed by thickening of the bilayer structure, partly due to a gauche- trans transition of lipid molecules but mainly due to redistribution of the solvent n-decane.

Animals↗

PubMed1989

[Effect of beta-lactam antibiotics on lipid bilayer membranes. II. Cephalosporin antibiotics].

Interaction of cephalosporin antibiotics with flat bilayer lipid membranes (BLM) composed of vegetative or bacterial phospholipids was studied with respect to their effect on electroconductivity, capacity for binding to the bilayers and capacity for transmembrane transfer through the bilayers. By their effect on conductivity, the investigated cephalosporins could be divided into three groups: those having no effect on conductivity at the maximum concentrations (up to 1 mg/ml) i.e. cefoperazone, cefotaxime and ceftizoxime, those having an effect on conductivity at concentrations of 0.2 to 0.5 mg/ml i.e. cephalexin and cephalothin and those having a significant effect on conductivity at concentrations of 10 to 60 micrograms/ml i.e. N-acyl derivative of 7-ACA (substance 64) and 7-ACA derivative (substance 71). The cephalosporins had a capacity for binding to the bilayers and for incorporation into the bilayers. They penetrated to some extent through the bilayers composed of either vegetable or bacterial phospholipids. The lower rate of penetration through the BLM as compared to that of penicillins must be due to lower hydrophobicity of the cephalosporin molecules as compared to that of penicillins.

Cephalosporins↗

PubMed2004

The study of the interaction of a model alpha-helical peptide with lipid bilayers and monolayers.

We studied the interaction of the alpha-helical peptide acetyl-Lys(2)-Leu(24)-Lys(2)-amide (L(24)) with tethered bilayer lipid membranes (tBLM) and lipid monolayers formed at an air-water interface. The interaction of L(24) with tBLM resulted in adsorption of the peptide to the surface of the bilayer, characterized by a binding constant K(c)=2.4+/-0.6 microM(-1). The peptide L(24) an induced decrease of the elasticity modulus of the tBLM in a direction perpendicular to the membrane surface, E(radial). The decrease of E(radial) with increasing peptide concentration can be connected with a disordering effect of the peptide to the tBLM structure. The pure peptide formed a stable monolayer at the air/water interface. The pressure-area isotherms were characterized by a transition of the peptide monolayer, which probably corresponds of the partial intercalation of the alpha-helixes at higher surface pressure. Interaction of the peptide molecules with lipid monolayers resulted in an increase of the mean molecular area of phospholipids both in the gel and liquid crystalline states. With increasing peptide concentration, the temperature of the phase transition of the monolayer shifted toward lower temperatures. The analysis showed that the peptide-lipid monolayer is not an ideally miscible system and that the peptide molecules form aggregates in the monolayer.

Adsorption↗

PubMed1998

Permeability of lipid bilayer to anthracycline derivatives. Role of the bilayer composition and of the temperature.

The uptake of three anthracycline derivatives: doxorubicin, daunorubicin and pirarubicin, into large unilamellar vesicles (LUV) in response to a driving force provided by DNA encapsulated inside the LUV has been investigated as a function of the temperature and of the bilayers lipid composition. The kinetics of the decay of the anthracycline fluorescence in the presence of DNA-containing liposome was used to follow the diffusion of the drug through the membrane. For the three drugs, the permeability coefficient of the neutral form of the drug (P0) decreases as the amount of negatively charged phospholipid in the bilayers increases. This can be explained by the fact that the kinetics of passive diffusion of the drugs depends on the amount of neutral form embedded in the polar head group region, which decreases as the quantity of negatively charged phospholipids increases. P0 also decreases as the amount of cholesterol, that makes the bilayer more rigid, increases. The activation energies, Ea, for the passage of the neutral form of these anthracyclines through the bilayers lie within 100 +/- 15 kJ x ml-1, except for pirarubicin and doxorubicin through anionic phospholipid-rich membranes (Ea = 57 kJ x mol-1) and cholesterol-rich membranes (Ea = 167 kJ x mol-1).

Antibiotics, Antineoplastic↗