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PubMed1990

Rimantadine effects on the elasticity of bilayer lipid membranes and on ion transport through gramicidin D channels.

The effect of the antiviral preparation rimantadine on lipid bilayer membranes (BLM) was studied by measuring the modulus of elasticity in the direction normal to the surface (E perpendicular) and by estimating the conductance lambda, the lifetime tau of single gramicidin D channels (GRD), and the coefficient of nonlinearity beta of current voltage characteristics (IVC) of GRD-modified BLM. Rimantadine induced a nonmonotonic change in E perpendicular of BLM prepared from a mixture of egg lecithin with cholesterol: at relatively low rimantadine concentrations (0-40 micrograms/ml) E perpendicular first increased, reached a maximum and started to decrease. The effectivity of rimantadine was dependent on the cholesterol concentration in the BLM. Changes in E perpendicular suggest an increased ordering of the lipid bilayer at low rimantadine concentrations and formation of clusters of the preparation at concentrations exceeding those necessary to obtain maximal values of E perpendicular for the given BLM lipid composition. Rimantadine concentrations lifetime by approximately 20 percent, affected the degree of IVC nonlinearity and superlinearity of GRD-modified membranes, which suggests some effect on the height of the barrier at the ionic channel mouth and in its centre.

Cholesterol↗

PubMed1990

Calmodulin interaction with mesocaine-modified lipid bilayer.

Calmodulin (CaM) interactions with bilayer lipid membranes (BLM) were studied by measuring modulus of elasticity in direction perpendicular to the membrane plane (E perpendicular) and intramembrane potential delta psi. Upon interaction of CaM with egg phosphatidylcholine and asolectin BLM the parameter E perpendicular grew slightly (not more than by 10% as compared to the respective vale for nonmodified BLM), suggesting a weak effect on the ordering of the hydrophobic moiety of the lipid bilayer. In the presence of mesocaine (Mes), a calmodulin inhibitor, CaM affected the incorporation of Mes into the membrane. It can be concluded that CaM affects the ordering of the polar (superficial) membrane region.

Acetanilides↗

PubMed1989

[Effect of beta-lactam antibiotics on lipid bilayer membranes. I. Penicillin antibiotics].

Interaction between penicillins and model membrane systems, flat black bilayer lipid membranes (BLM) composed of vegetable or bacterial phospholipids was studied with an account of the complicated structure of bacterial cell membranes and possible presence in them of "pure" bilayer lipid areas. By their effect on electroconductivity of the BLM the antibiotics could be divided into three groups: those having no effect on the BLM electroconductivity at the maximum concentrations i.e. benzylpenicillin, carbenicillin, piperacillin (at pH 6.0 and 7.0) and ampicillin (at pH 6.0), those insignificantly changing electroconductivity of the BLM i.e. carfecillin and azlocillin and those having a significant effect on the BLM electroconductivity i.e. ampicillin N-acyl derivatives and 6-APA. The effect of ampicillin on the BLM conductivity markedly depended on the electrolite pH. The penicillins bound to the bilayer and induced changes in the transmembrane potential (evident from the changes in the second harmonic of the capacitive current) and the BLM elasticity-capacitance parameters (evident from the changes in the ratio of the amplitudes of the first and third harmonics). It was shown that all the penicillins penetrated through the BLM composed of either vegetable or bacterial phospholipids. The capacity for the transmembrane transfer without changing of the bilayer conductivity must be connected with the fact that the penetrating antibiotics did not induce any changes in the BLM structure. The effect on the conductivity probably depended in its turn on the form of the molecule and the ratio of the hydrophilic and hydrophobic parts in it.

Electrolytes↗

PubMed1990

Structure of polymerizable lipid bilayers: water profile of a diacetylenic lipid bilayer using elastic neutron scattering.

Elastic neutron scattering experiments have been used to study the hydration of multibilayers of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC). Previously published FTIR spectroscopic data had suggested, based on shifts in the carbonyl (C = O) stretch frequencies, that the phosphocholine headgroup in these polymerizable lipid bilayers was much less hydrated than that of saturated phosphatidylcholines. Our results demonstrate that the DC8,9PC headgroup is at least as well hydrated as that of dipalmitoylphosphatidylcholine (DPPC), a saturated lipid, under the same conditions.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1989

Conductance transition induced by an electric field in lipid bilayers.

A cooperative phenomenon showing a structural change in the organization of bilayer lipid membranes at a critical value of the applied electric field is presented. The transition is characterized by a sharp increase in conductance. The phenomenon can be observed under current-clamp conditions (rather than the usual voltage-clamp conditions) to avoid rupturing the membrane. At a critical potential value the conductance increases and therefore the potential decreases to keep the current constant. Results refer to membranes made of egg phosphatidylcholine (PC), diphytanoylphosphatidylcholine and cholesterol/egg PC. It is found that the critical potential at which the transition occurs depends dramatically on pH and ionic concentration, indicating that the electrical properties of the external surface determine the major characteristics of such a transition.

Cholesterol↗

PubMed1990

Detection of transient capacitance increase associated with channel formation in lipid bilayers.

The insertion of alpha- and beta-latrotoxins and sea anemone (Radianthus macrodactilus) toxin into bilayer lipid membranes (BLMs) was investigated using the method of simultaneous conductance/capacitance measurement. All the toxins investigated induced capacitance changes which preceded toxin-induced conductance increases. The processes that may underlie the observed effect are discussed.

Animals↗

PubMed1990

Effects of local anesthetics on mechanical characteristics of lipid bilayers and on the ion transport dynamics.

Bilayer lipid membranes (BLM) of various composition were used to study the effects of local anesthetics (LA) carbisocaine and lidocaine on mechanical membrane characteristics and on the transport dynamics of ions across gramicidin D ionic channels. Carbisocaine concentrations of 20 mumols/l-0.1 mmol/l caused a considerable decrease (by 15-40%) in modulus of elasticity E1 in direction perpendicular to membrane surface. The effect of lidocaine was approx. one order of magnitude weaker. LA-induced changes in E1 were shown to depend on both the lipid composition of the membrane and the electrolyte pH. Neutral forms of LA induce marked changes in E1. An analysis of current-voltage (I-V) characteristics of BLM modified by the channel forming agent gramicidin D revealed that carbisocaine significantly affects the superlinear segment of the I-V relationship; this suggests a strong effect on the transport dynamics of ions through the internal channel region. The results of the study suggest that the action of both carbisocaine and lidocaine may be non-specific. The effectivity of the non-specific action of LA is determined by the hydrophobic moiety of the local anesthetic molecule.

Anesthetics, Local↗

PubMed1990

[Modeling of damage to cell membranes during photodynamic therapy: photosensitization of planar lipid bilayers by hematoporphyrin dimethyl ether].

The variations of electrical conductance of planar bilayer lipid membranes (BLM) sensitized by hematoporphyrin dimethyl ether under visible light illumination were studied. The conductance of BLM does not change for some period after switching on the light, then an increase in the conductance starts and the membrane breaks. This "induction" time does not depend on addition of azide or ferricyanide to the solution, on addition of BHT to the lipid and on substitution of air for argon in the cell. The induction time for any new BLM, formed in the same cell immediately after the previous membrane was broken, is shorter. The variation of BLM boundary potentials during induction time was not observed. The results obtained suggest that the photodamage of BLM sensitized by HPD leads to accumulation of uncharged reaction products and oxygen does not take part in this process.

Cell Membrane↗

PubMed1990

Polarity-dependent voltage-gated porin channels from Escherichia coli in lipid bilayer membranes.

A porin preparation from Escherichia coli 0111:B4 consisting of Omp F and Omp C (with Omp F in excess) was purified by salt extraction procedures and investigated in bilayer lipid membranes formed according to the Montal-Mueller technique. The porin preparation was added to the KCl electrolyte compartment of the Montal-Mueller cell which was connected to the voltage source. As the porin incorporated into the membrane, asymmetric, voltage-gated ion channels were formed. Transmembrane voltages greater than +50 mV (measured with respect to the side of porin addition) caused channel closing, while negative voltages, on the other hand, had no effect on channel behaviour but did increase the rate of porin incorporation at higher voltages. With porin added to both compartments voltage gating no longer occurred. Single-channel conductances corresponded to effective pore diameters of 1.5 nm for opening events and 1.18 nm for channel closing events. The number of charges involved in gating was approximately 2.

Bacterial Outer Membrane Proteins↗

PubMed1992

The mode of action of Vibrio cholerae cytolysin. The influences on both erythrocytes and planar lipid bilayers.

The interaction with erythrocytes of cholera cytolysin (CC) obtained from a non-01 Vibrio cholerae strain results in the osmotic rupture of target cells upon formation by CC of the waterfilled pores in their membranes. The aggregation of several toxin monomers is required for the formation of one CC channel with a radius of 0.9-1.0 nm. The investigations using planar bilayer lipid membranes suggest that the CC-induced pore is an interprotein anion selective channel carrying a fixed positive charge. The role of the charge was supported by the influence of pH on the selectivity, single conductance and voltage gating of the CC channels. The ability of the CC to modify both model and natural membranes has a maximum at pH 6.0-7.0. It was found that CC channels insert into the membrane asymmetrically. The effect of proteolytic treatment of the channel by papain also indicates that the two entrances of the channel protrude from the plane of the membrane into the solution for different distances. It is proposed that the biological effects of the non-01 V. cholera cytolysin are based on its channel-forming activity.

Animals↗

PubMed1991

Modulation of a gated ion channel admittance in lipid bilayer membranes.

A future class of amperometric biosensors may utilize gated ion channels such as acetylcholine and glutamate receptors as chemical detection components. In this study, bilayer lipid membranes containing voltage-dependent anion channels (VDAC) were used to model an ion-channel-based biosensor which could continuously monitor AC amperometric changes resulting from induced changes in channel conductance. The in-phase and quadrature components of the induced alternating membrane current were monitored as a function of the applied DC offset voltage which was superimposed on the sinusoidal test voltage. The accuracy and sensitivity of the AC-measured VDAC response was dependent on the magnitude of the AC test voltage relative to the DC offset necessary for channel closure. The VDAC channel appears to be a suitable model protein for AC impedance-based biosensor fabrication.

Biosensing Techniques↗

PubMed1986

Spontaneous lipid bilayer transmembrane electrical oscillations induced by concanavalin A-polysaccharide interaction.

Potassium ion currents through bilayer lipid membranes were modified by the membrane-surface reaction of concanavalin A and the polysaccharides dextran and glycogen. Aggregative reaction with glycogen occasionally induced spontaneous periodic ion current fluctuations with cycle times of minutes and durations of over one hour. Different electrochemical characteristics were observed between large planar lipid membranes and filter paper supported membranes, providing an indication that the aqueous unstirred surface layer participates in the control of the surface aggregative event. Lipid chemical composition was implicated in the development of spontaneous oscillations.

Concanavalin A↗

PubMed1992

Comparison of 9-aminoacridine and atebrine induced changes in optical, electrical and mechanical characteristics of lipid bilayers.

The effects of fluorescent probes 9-aminoacridine (9AA) and atebrine (AT) on physical properties of liposomes and planar bilayer lipid membranes (BLM) were studied. The method of fluorescence spectroscopy and the electrostriction method based on measurement of higher current harmonics were used. At low concentrations (10(-5)-5 x 10(-5) mol/l), 9AA increased fluorescence intensity, while in liposomes from soybean phosphatidylcholine fluorescence quenching occurred at higher probe concentration. Fluorescence quenching occurred over the entire concentration range tested (10(-5)-10(-4) mol/l) in liposomes made from a mixture of egg phosphatidylcholine and cardiolipin. In contrast to 9AA, AT, thanks to its hydrophobic chain, penetrates deeper into the hydrophobic membrane moiety; thus, immobilization of the molecule and an increase in fluorescence intensity was always observed. Probes adsorbed to membranes, leaving their electric capacitance effectively unchanged. Adsorption of charged dye particles induced small changes in transmembrane potential. In the presence of 10(-5) mol/l AT, the modulus of elasticity E perpendicular increased somewhat for soft membranes (E perpendicular approximately 2.5 x 10(7) Pa), whereas it decreased for hard membranes (E perpendicular approximately 5 x 10(7) Pa). pH gradient present on the membrane affected the ability of the dyes to incorporate into the membranes. Our results provide evidence against the proposed model of the quenching mechanism introduced by Rottenberg and Lee (1975).

Aminacrine↗

PubMed1992

Haematoporphyrin changes the mechanical properties of lipid bilayer membranes.

The interactions between haematoporphyrin (HP) and bilayer lipid membranes (BLM) were studied. A weak effect of HP on BLM conductivity was observed at HP concentrations ranging between 10(-6) and 3 x 10(-5) mol/l. Modulus of elasticity in the direction normal to the membrane plane (E perpendicular) and dynamic viscosity coefficient (eta) were measured, both exhibiting HP-induced decrease by 22-31% in the dark. In this case, membrane potential Vm became negative and reached a value close to -50 mV. Under illumination by low-intensity (1 mW) He-Ne laser (lambda = 632 nm) the values of parameters E perpendicular and eta of the HP-modified membranes increased by 41-66%, and Vm decreased to -20 mV. Upon removing HP from the solution by perfusion, irreversible changes in mechanical properties of the HP-modified membranes induced by the laser light were observed. The reason could be the formation of stable complexes of HP with the lipid molecules. HP binds to membrane noncooperatively, with a binding constant K approximately 10(5) l/mol.

Binding Sites↗

PubMedDate not supplied

[Ionic selectivity of melittin-modified flat lipid bilayers].

It has been established in experiments with the bilayer lipid membranes (BLM) that at pH greater than 6.6 the melittin pores are cation-selective and at lower pH they are more selective by anions. The property of melittin pores is shown to be provided by the amino group of the N-terminal glycine residue. The selectivity of melittin-containing membranes may be controlled by the transmembrane potential, the cross-section of water pores being changed. The data obtained are explained within the alimethicine-like model.

Bee Venoms↗

PubMedDate not supplied

[Aperiodic oscillations of the lipid bilayer potential during enzymatic hydrolysis of the permeating substrate].

The experimental system contained a solution with substrate ATEE-ether, a planar bilayer lipid membrane doped with a protonophore and solution with proteolytic enzyme. Oscillations of the electrical potential on the membrane were shown. The magnitude of the potential was proportional to the rate of the reaction under these conditions. This system may prove useful for the study of the peculiarities of enzyme kinetics complicated by the membrane.

Hydrolysis↗

PubMedDate not supplied

[Relation between gramicidin D and valinomycin-induced conductivity of lipid bilayer and cholesterol levels].

Kinetics of conductance and current-voltage characteristics (VACH) were studied on the bilayer lipid membranes from egg lecithin and cholesterol modified by gramicidin D and valinomycin. There were found significant changes of ionic channels conductance g, lifetime tau and non-linearity coefficient beta of VACH of modified membranes dependent on cholesterol content. In the region of high cholesterol concentrations, more than 20 mol%, there were observed abrupt changes of the ionic channels parameters: tau increased more than ten times, conductance decreased two times and beta greater than 0 in the whole region of electrolyte concentration.

Cholesterol↗

PubMedDate not supplied

[Stimulation of gramicidin incorporation into lipid bilayer membranes by ultrasound].

Ultrasound effect on gramicidin incorporation into a bilayer lipid membrane has been investigated. The observed increase in the channel opening frequency points to the incorporation rate growth due to the thickness diminishing of near-membrane non-stirred layers. The dependence of ultrasound intensity on the layer thickness is presented.

Gramicidin↗