The changes of capacitance relaxation of bilayer lipid membranes induced by chlorpromazine.
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Chemical Phenomena↗
Biomedical subjects
T Hianik
Publications and source records attributed to T Hianik.
The parametric pump mechanism in separation of components in heterogeneous systems. I. Macroscopic distributed systems.
A dynamic method is proposed for the separation of the electrolyte components using a parametric pump with an ion exchange column. It was studied experimentally and described mathematically. The parametric separation of mixtures is based on interactions of two oscillating fields with a heterogeneous system containing two phases, a liquid and a solid one, the components of the mixture being able to redistribute between the phases. The field of mechanical force is responsible for cyclic relative displacement of the phases, and synchronously changing temperature causes redistribution of the components between them. This results in sodium and potassium fluxes opposite in direction which in turn leads to accumulation of sodium and potassium in opposite end cells.
Chemical Fractionation↗
Cholesterol-induced variations in the volume and enthalpy fluctuations of lipid bilayers.
The sound velocity and density of suspensions of large unilamellar liposomes from dimyristoylphosphatidylcholine with admixed cholesterol have been measured as a function of temperature around the chain melting temperature of the phospholipid. The cholesterol-to-phospholipid molar ratio xc has been varied over a wide range (0 </= xc </= 0.5). The temperature dependence of the sound velocity number, of the apparent specific partial volume of the phospholipid, and of the apparent specific adiabatic compressibility have been derived from the measured data. These data are particularly discussed with respect to the volume fluctuations within the samples. A theoretical relation between the compressibility and the excess heat capacity of the bilayer system has been derived. Comparison of the compressibilities (and sound velocity numbers) with heat capacity traces display the close correlation between these quantities for bilayer systems. This correlation appears to be very useful as it allows some of the mechanical properties of membrane systems to be calculated from the specific heat capacity data and vice versa.
Biophysical Phenomena↗
Weak nonlinearity of current-voltage characteristics of gramicidin D channels. Experiment, theory and application to the study of transmembrane transmission of information.
A new, sensitive method of measurement of current-voltage characteristics (CVC) of the type i(U) approximately U(1 + beta U2) was applied to study ionic channels formed by gramicidin D in bilayer lipid membranes (BLM). The values of the non-linearity coefficient beta of the CVC of membranes modified by gramicidin D depended on electrolyte concentration, C, and expressed the weak nonlinearity of the CVC. In symmetric electrolyte conditions, the coefficient beta(A) increased with the increasing electrolyte concentration from -17 V-2 at 0.03 mol/l KCl to 8 V-2 at 3 mol/l KCl. In asymmetric electrolyte conditions (different electrolyte concentrations at the two sides of the BLM) the coefficient beta(A) also increased with increasing C. A theory is proposed describing the weak nonlinearity of CVC of ionic channels based on electrodiffusion model. This theory assumes that the electrochemical potential mu(x) of an ion within the ion channel depends on the coordinate x along the channel axis. According to the proposed model, CVC nonlinearity is mainly determined by the ends of the ion channel. We showed that the structure of gramicidin D ionic channel is sensitive to the concentration of ions, and in fact changes at one end of the channel influence the parameters of the other channel end.
Electrochemistry↗
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↗
Molecular acoustic as a new tool for the study of biophysical properties of lipoproteins.
The method of measurement of velocity and absorption of ultrasound at a fixed frequency (7.2 MHz) and measurement of density were used to study the physical properties of high- (HDL3) and low- (LDL) density lipoproteins. We found substantial changes in velocity number [u] and absorption number [alpha lambda] on temperature, which reflect structural changes in the hydrophobic core of LDL at the thermotropic-phase transition. The absorption number revealed broad changes in temperature for both classes of lipoproteins (LP). The density of LP also depends on temperature but in considerably less degree than the acoustic parameters. The values of acoustic parameters were determined, showing that LDL and HDL3 greatly differ with respect to adiabatic compressibility.
Acoustic Stimulation↗
Interaction of adrenocorticotropin-(1-24)-tetracosapeptide with lipid bilayers.
The interaction of the peptide hormone adrenocorticotropin with solvent-free planar lipid bilayers (BLM) and liposomes was studied by measurements of elasticity modulus perpendicular to the plane of the membrane (E perpendicular, measured by electrostriction), surface potential difference (delta phi m), electrical capacitance, capacitance relaxation following a voltage jump (yielding relaxation times for molecular dipoles or dipolar domains), and fluorescence polarization. Addition of the 6-fold positively charged peptide to one side of the membrane leads to a more positive membrane surface potential, an increase of BLM capacitance, a decrease of elasticity modulus, and faster relaxation time constants. This also caused a decrease of DPH fluorescence anisotropy of the liposome suspension modified by fluorescent dye DPH. Mixed BLM of palmitoyl-oleoyl-phosphatidylcholine (POPC)+soybean phosphatidylcholine (SBPC) (10:1 w/w), which carry a negative surface charge, exhibit considerably larger changes than electroneutral POPC membranes. Our results confirm that ACTH1-24 binds to BLM and interacts with the hydrophobic part of the bilayer.
Cosyntropin↗
Can a single bacteriorhodopsin molecule change the structural state of one liposome?
Using ultrasonic velocity measurements the interaction of bacteriorhodopsin (BR) with large unilamellar liposomes of dipalmitoylphosphatidylcholine (DPPC) was studied in gel (25 degrees C) and in liquid crystalline state (50 degrees C) of lipid bilayer. We could show that with the increasing BR concentration the increment of ultrasonic velocity increases and a saturation occur at a BR/Liposomes of ratio approximately 0.5 mol/mol. BR incorporation into the lipid bilayer in gel state leads to an increase of the increment of the ultrasonic velocity of the lipid to 9.51 +/- 1.47 ml/mol. This could be mainly attributed to a decrease in membrane compressibility or an increase in membrane volume or both. No changes of ultrasonic velocity increment were observed with the membrane in liquid crystalline state. In this case, BR probably is not able to change the mechanical properties of a considerably disordered membrane.
1,2-Dipalmitoylphosphatidylcholine↗
Acoustical investigation of the liposome-saccharide interaction.
High precision measurements of ultrasonic velocity in aqueous suspension of phosphatidylcholine liposomes in the presence of trehalose, sucrose and glucose have demonstrated its dependence on the concentration of the two disaccharides. This finding is interpreted in terms of replacement by the latter of water molecules bound to phosphate head groups on the liposome surface.
Acoustics↗
Viscoelasticity of BLM from choline plasmalogen, alkylacyl- and diacyl-glycerophosphocholines.
Mechanical characteristics of bilayer lipid membranes (BLM) composed of alkenylacyl-, alkylacyl-, and diacyl-glycerophosphocholines were studied by measuring modulus of elasticity in the direction normal to BLM plane, E perpendicular, and coefficient of dynamic viscosity eta. Alkenylacyl-glycerophosphocholine (choline plasmalogen) BLM typically show larger values of E perpendicular and eta as compared to their analogs, suggesting a tighter packing of their hydrophobic regions. Increasing cholesterol concentrations are associated with monotonically increasing values of parameters E perpendicular and eta of plasmalogen BLM, whereas a nonmonotonic dependence of these parameters with a maximum around c = 66 mol% cholesterol is typical for the diacyl analog POPC. This may be due to the formation of cholesterol clusters at c > 66 mol%.
Cholesterol↗
Clustering of cholesterol in DMPC bilayers as indicated by membrane mechanical properties.
Mechanical characteristics of bilayer lipid membranes (BLM) composed of dimyristoylphosphatidylcholine (DMPC) and cholesterol in the gel and liquid crystalline state were studied by measuring the modulus of elasticity in direction perpendicular to the BLM plane, E perpendicular. The value of E perpendicular varied nonmonotonically with the cholesterol concentration, with a maximum around c = 50 mol% cholesterol. E perpendicular of BLM in gel state was about 2 times higher than that measured for the liquid crystalline state but the shape of E perpendicular (c) curves was similar for both states of the membrane. This may be due to the formation of cholesterol clusters at c > 50 mol% in both phase states of BLM.
Cholesterol↗
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↗
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↗
[A model for the study of mechanical properties of membranes during hormone binding].
Bilayer lipid membranes (BLM) were used to reconstitute the hormonal reception system for insulin and glucagon. The effect of the hormones on both BLM and BLM with incorporated rat liver plasma membrane fragments (BLM-PM) was studied by measuring the elastic parameter of membranes--the Young modulus of elasticity in the direction perpendicular to the membrane plane (E perpendicular)--using an electroconstriction method. The effect of insulin (in a concentration of 10(-10) mol.l-1) on BLM-PM resulted in a much greater (about threefold) decrease of E perpendicular) compared to that on BLM. The high content of cholesterol had a strong inhibitory effect on this interaction. The effect of the insulin antagonist glucagon on BLM-PM resulted in opposite changes of the relative value of E perpendicular compared to the effect of insulin. While the effect of insulin resulted in a relative decrease of E perpendicular by about 60%, glucagon in the same concentration induced a relative increase of E perpendicular by about 8%.
Animals↗
Angiotensin II-induced formation of ionic channels in bilayer lipid membranes.
The interaction of angiotensin II (ANG II) with membrane was studied by measuring conductance and current-voltage characteristics (IVC) of bilayer lipid membranes (BLM) prepared of a mixture of egg lecithin with cholesterol, and of gramicidin D-modified membranes of the same composition. Addition of physiological concentrations of ANG II (approx. 15 mumol/l) into the electrolyte (1 mol/l KCl, pH = 7) in contact with one side of BLM resulted in the appearance of discrete membrane conductance (symbol; see text) = (39.5 +/- 1.07) pS with a duration of the conductivity state tau = (52.15 +/- 6.44) s. Raising ANG II concentration to 75 mumol/l resulted in an additional conductance level of approx. 130 pS with a lifetime of approx. 1s. The electrolyte pH markedly influenced ANG II modified BLM conductance. A decrease of the electrolyte pH to 2.8 resulted in a reduction of the discrete conductance level to approx. 14 pS, whereas ANG did not induce any conductivity at pH = 11.5. The results obtained suggest that ion channels are formed consisting at least of two ANG II molecules. IVC of ANG II-modified BLM are superlinear within the range of electrolyte concentrations studied (between 0.01 and 3 mol/l KCl), i.e, the limiting stage of ion transport is the internal area of the conducting pore. ANG II affects in a cooperative manner the gramicidin D (GRD)-mediated transport, most likely by forming ANG II aggregates in the area of local inhomogeneities in the BLM structure of GRD channels.
Angiotensin II↗
[The effect of cholesterol on parameters of gramicidin D ion channels and on the macroscopic and microscopic characteristics of lipid bilayers].
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Cholesterol↗
Thermodynamical characteristics and volume compressibility of dipalmitoylphosphatidylcholine liposomes containing bacteriorhodopsin.
The effects of bacteriorhodopsin (BR) interaction with large dipalmitoylphosphatidylcholine (DPPC) liposomes (approx. 100 nm in diameter) were examined at various BR/DPPC ratios, using differential scanning calorimetry (DSC) and ultrasonic velocimetry (USV). On DSC, the lipid phase transition temperature, Tc, and the half-width of the phase transition peak, delta T1/2, showed significant non-monotonic changes with the increasing BR concentration. Two exponential segments could be distinguished in the dependence of the transition enthalpy change per mol of lipid (delta H/nL) on the BR/DPPC ratio: one corresponding to ratios between 0:1 and 1:64, and another corresponding to ratios between 1:44 and 1:16. A maximal value of delta H/nL was observed for BR/DPPC ratio 1:44, probably corresponding to maximal BR-lipid ordering with each BR molecule being surrounded by two layers of lipid molecules. The nonmonotonic changes of thermodynamical parameters suggest long-distance interactions between regions of altered bilayer structure which form around each BR molecule. The results obtained with USV provided support for the above conclusions. The dependence of ultrasound velocity increment A on BR concentration supplies information on relative changes of membrane volume compressibility. Decreasing volume compressibility is reflected in increasing values of parameter A. Within T less than Tc, the values of A increased with the increasing BR concentration; saturation was observed at BR/DPPC ratio 1:500 (A = A(BR/DPPC]. No significant BR-concentration dependent changes of A were observed at T greater than Tc. From these values the average diameter of the distorted region of lipid bilayer was estimated to be approximately 20 nm.
1,2-Dipalmitoylphosphatidylcholine↗
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↗