Molecular motions in a liquid-crystalline lipid bilayer. Molecular dynamics simulation

The results of a molecular dynamics study of a lipid bilayer are discussed. As a model we consider an ensemble of 2 × 10 flexible chains consisting of 16 groups in a box with lateral (x, y) periodicity conditions. The chains interact with each other and with the aqueous medium. Terminal groups are bound near to the bilayer surfaces by a harmonic potential. All numerical results are compared with those obtained for an isotropic polymer liquid with the same density as for the bilayer. From a study of the order parameters we conclude that the bilayer is in the liquid-crystalline state with the chains expanding in the z-direction normal to the surfaces. Segmental order parameters are in reasonable agreement with experimental NMR data. Dynamic properties discussed include the frequency spectrum of the velocity autocorrelation function of particles, the incoherent dynamic structure factor, dielectric absorption, and luminescence polarization. It is found that compared with the bulk polymer liquid, the molecular motions in the bilayer are quite different. Such features arise mainly from existing strong correlations in the bilayer and from a different molecular organization of the chains in the bilayer and in the bulk liquid.     

Cell adhesion to protein-micropatterned-supported lipid bilayer membranes

A new method for constructing controlled interfaces between cells and synthetic supported lipid bilayer membranes is reported. Microcontact printing is used to define squares and grid lines of fibronectin onto glass, which subsequently direct the self-assembly of fluid lipid bilayers onto the complementary, uncoated regions of the surface. Features of fibronectin as small as 5 microm effectively control the lateral organization of the lipid bilayers. These fibronectin barriers also facilitate the adhesion of endothelial cells, which exhibit minimal adhesion to fluid supported lipid bilayers alone. Cells selectively adhere to the features of fibronectin, spanning over and exposing the cells to the intervening regions of supported lipid bilayer. Cell spreading is correlated with both the geometry and dimensions of the fibronectin barriers. Importantly, lipids underlying adherent cells are laterally mobile, suggesting that, in contrast to the regions of fibronectin, cells were not in direct contact with the supported membrane. Protein micropatterning thus provides a valuable tool for controlling supported membranes and for juxtaposing anchorage-dependent cells with lipid bilayers. These systems should be generally useful for studying specific interactions between cells and biomolecules incorporated into supported membranes, and as an approach for integrating living cells with synthetic, laterally complex surfaces.     

Effect of leukemia-inhibiting factor on bilayer lipid membrane

We studied the effect of leukemia-inhibiting factor on bilayer lipid membranes. Leukemia-inhibiting factor in a concentration of 10 ng/ml nonspecifically increased membrane permeability for ions. Leukemia-inhibiting factor acts as a surface-active substance on bilayer lipid membranes.     

Antigen-antibody-complement reaction studies on micro bilayer lipid membranes

The ion permeability of lipid membranes formed on Millipore and Nuclepore filters has been found to exhibit stepwise reductions in electrical resistance in the presence of Forssman antigen, appropriate antiserum and complement. The results appear to support the "hydrophobic doughnut" or transmembrane channel hypothesis, which envisions several polypeptide chains anchoring from more than one terminal complement component to interact with one another within the lipid bilayer. Channel formation in these artificial membranes is believed to be due to the insertion of complement proteins. Concentrations and temperature studies were carried out to ascertain that the electrical responses were owing to the generation of stable channels by complement across the membrane. The diameter of these channels was estimated to be in the order of 100 A.     

The effect of metal chelators on lipid peroxidation in irradiated erythrocytes.

Prophylactic irradiation of blood and blood components is accepted practice in order to prevent graft-versus-host disease from infused lymphocytes. Irradiation, however, results in increased red cell potassium (K+) loss, along with other possible effects that may affect red cell function and viability. Lipid peroxidation (LP), a process initiated by the production of oxygen free radicals, is increased in red cells in the presence of reactive iron species and various heme moieties. In this report, it is noted that not only is plasma K+ significantly increased following blood irradiation, but LP is also increased compared with paired non-irradiated blood samples. Furthermore, various metal chelators significantly reduce LP in the irradiated samples. These chelators also significantly reduced the rate of cellular K+ loss during the four day 37 degrees C incubation period. This study further suggests that the addition of selected metal chelators may be effective in both irradiated and non-irradiated stored blood by improving the function and viability of transfused erythrocytes.     

Light scattering studies of viscose solution

Viscose has been fractionated and the fractions as well as the gross polymer have been characterized by the light scattering technique. The molecular weight, shape and the root mean square end to end distance of the gross polymer and its two fractions have been determined. The gross polymer as well as the fractions obtained therefrom have been found to possess random coil configuration. The molecular weight of the gross polymer and its two fractions are 5.65·10⁵, 1.205·10⁶, and 3.63·10⁵, respectively. The root mean square end to end distance is 1435 Å. for the gross polymer, and 1997 Å. and 1614 Å. for the first two fractions, respectively.     

Reconstitution of brain mitochondria inner membrane into planar lipid bilayer

Ion channels are present in the inner mitochondrial membrane. They play an important role in cellular processes. Potassium and chloride channels are involved in regulation of mitochondrial volume, membrane potential and acidification. The mitochondrial potassium channels have been suggested as triggers and end effectors in cytoprotection. In our study we measured single channel activities after reconstitution of submitochondrial particles from rat brain mitochondria into planar lipid membranes. After incorporation, two different potassium selective currents were recorded with single channel conductance from 260 to 320 pS and from 70 to 90 pS in gradient (cis/trans) 50/450 and 50/150 mM KCl solutions, respectively. We also observed activity of the chloride ion channel. The measured single channel conductance was from 80 to 90 pS in gradient (cis/trans) 50/450 mM KCl solution. Our results suggest that various ion channels are present in the inner mitochondrial membrane of brain mitochondria.     

Cationic lipid bilayer coated gold nanoparticles-mediated transfection of mammalian cells

Here, we demonstrated dimethyldioctadecylammonium bromide (DODAB), a cationic lipid, bilayer coated Au nanoparticles (AuNPs) could efficiently deliver two types of plasmid DNA into human embryonic kidney cells (HEK 293) in the presence of serum. The transfection efficiency of AuNPs was about five times higher than that of DODAB. The interaction of AuNPs with DNA was characterized with dye intercalation assay and agarose gel electrophoresis. The morphology of the complex of AuNPs with DNA was observed with scanning electron microscope (SEM). The intracellular trafficking of the complex was monitored with transmission electron microscope (TEM). Based on experimental results, the possible mechanism was proposed and the barriers in the process of transfection were discussed. This work demonstrates a simple way to increase the transfection efficiency of cationic lipid through changing the stability of the complex of cationic lipid with DNA. It may provide some insights into understanding and controlling the interaction of cationic lipid with DNA. It also provides a novel way to construct gold nanoparticles-based gene vectors and some insights into learning the process of nanomaterials-mediated transfection.     

Reconstitution in lipid bilayer of smooth muscle cation channels activated through a GTP-binding protein.

Reconstitution of G-protein-coupled receptor activated cation channels into the lipid bilayer was attempted with plasma membrane vesicles prepared from guinea-pig ileal smooth muscle using the purification technique previously applied to the large conductance Ca2+-dependent and ATP-sensitive K+ channels (Toro et al., 1990). Under Na+-rich conditions, incorporation of plasma membrane vesicles into the bilayer produced GTPgammaS (100 microM)-activatable channel activities that are inhibited by GDPbetaS (1 mM), sensitive to Ca2+ and enhanced by depolarization. The reversal potential and unitary conductance (tens of picosiemens) of these channels varied in a manner dependent on Na+ concentration, but not affected by Cl-. These results strongly indicate that the reconstituted channels activated by GTPgammaS belong to a class of voltage-dependent, Ca2+-sensitive cation-selective channels that are activated through a G-protein, and correspond most likely to the muscarinic receptor-activated cation channels previously identified in the same preparation. These results also suggest potential usefulness of bilayer incorporation technique to investigate the receptor-operated cation channels in smooth muscle.     

Biomembrane-mimicking lipid bilayer system as a mechanically tunable cell substrate

Cell behavior such as cell adhesion, spreading, and contraction critically depends on the elastic properties of the extracellular matrix. It is not known, however, how cells respond to viscoelastic or plastic material properties that more closely resemble the mechanical environment cells encounter in the body. In this report, we employ viscoelastic and plastic biomembrane-mimicking cell substrates. The compliance of the substrates can be tuned by increasing the number of polymer-tethered bilayers. This leaves the density and conformation of adhesive ligands on the top bilayer unaltered. We then observe the response of fibroblasts to these property changes. For comparison, we also study the cells on soft polyacrylamide and hard glass surfaces. Cell morphology, motility, cell stiffness, contractile forces and adhesive contact size all decrease on more compliant matrices but are less sensitive to changes in matrix dissipative properties. These data suggest that cells are able to feel and respond predominantly to the effective matrix compliance, which arises as a combination of substrate and adhesive ligand mechanical properties.     

Platelet adhesion on to polyamide microcapsules coated with lipid bilayer membrane

Polyamide microcapsules with diameters of 3-4 microns were coated with lipid bilayer membrane and their interaction with canine platelets was investigated. Platelet adhesion on to the microcapsules was significantly suppressed by the lipid-coating. Coating with dimyristoylphosphatidylcholine (liquid-crystalline state) reduced platelet adhesion on to the microcapsules to a greater extent than that with dipalmitoylphosphatidylcholine (gel state) at 37 degrees C. The surface properties of the microcapsule in adsorption of plasma proteins were also changed by lipid coating. The amount of gamma-globulin and fibrinogen adsorbed on to the microcapsule was slightly decreased by lipid coating, while the amount of adsorbed albumin was increased. Platelet adhesion on to the lipid-coated microcapsules was suppressed most strongly in the presence of gamma-globulin. Apparently platelet adhesion on to the polyamide microcapsules is controlled by the nature of lipid membrane and gamma-globulin adsorbed on to the microcapsules.     

Light scattering studies on acacia catechuic acid in ethanol-water-mixtures

The light scattering properties of Acacia Catechuic Acid (ACA) was studied in aqueous mixture of ethanol containing 0.02 mole/l. KCl. There was hardly any effect upto 25% alcohol, above which the molecular weight appeared to increase gradually till 50% alcohol in the mixture and at 55% there was precipitation of the acid. The root mean square end-to-end distance remained almost unaffected at lower concentration and reached a minimum value at about 25% (3052 Å) beyond which there was considerable increase reaching up to a maximum limit of 3597 Å at 50% (as against 3270 Å in water). This interesting behaviour of ACA in the above mentioned system could be explained in the light of the FLORY-FOX equation in conjunction with association of molecules by their hydrophobic groups which was favoured by addition of alcohol. Alcohol, however, at low concentrations did not appear to affect the character of the solvent to a great degree but beyond about 25%, the solvent behaved as a poor one.     

A tissue culture bilayer model to study the passage of Neisseria meningitidis.

A tissue culture bilayer system has been developed as a model to study the mechanisms of attachment and invasion involved in the pathogenesis of Neisseria meningitidis. The model incorporates epithelial and endothelial cell layers separated by a microporous membrane and makes it possible to observe and quantify the passage of bacteria through the multiple layers and to study the mechanisms by which they make this passage. This model is adaptable to a wide variety of microbial pathogens and can be modified by substituting any physiologically relevant eucaryotic cells for the component layers. The system's makeup of cells of human origin and its reproducibility give it advantages over animal and primary organ culture models, while the added complexity of multiple layers allowing cell-to-cell communication makes it a more realistic human tissue model than standard cell monolayers.     

Light scattering peaks from aqueous solutions of acrylamideacrylic acid copolymers

Aqueous solutions of acrylamide-acrylic acid copolymers of high molecular weight have been investigated by light scattering. It was shown that a scattering peak can be obtained if the samples used have been prepared by alcaline hydrolysis of polyacrylamide and if the solutions are filtered and sonicated. In the range of the lower concentrations, the position of this peak, q*, is found to vary with the polymer concentration C, as C^1/3, and to be independent of the charge density. The addition of very small amounts of salt provokes the disappearance of the peak. A phase diagram (charge density versus concentration of the polymer) has been established. It shows that these experiments were carried out in a concentration range intermediate between the dilute and the semidilute regimes (transition regime). The experimental scaling laws however correspond to the theoretical predictions for the dilute regime. Moreover, the q* values are much lower than those calculated by the random phase approximation theories.     

Intestinal spirochaetosis. Light and electron microscopic study

24 cases of colon spirochaetosis have been studied by light and electron microscopy. This condition, although rarely diagnosed because of the absence of special clinical symptoms, seems to be a rather frequent histologic finding with marked variation in its geographical incidence. In our material the incidence of spirochaetosis was 16.5%, almost double than in Great Britain.     

Light scattering of polymethylmethacrylate solutions in binary solvent mixtures. Part 2. In acetone/benzene mixtures

An isotactic and an atactic polymethylmethacrylate have been investigated by light scattering measurements at 25°C in acetone/benzene mixtures in order to see the effects of the difference in the microstructures between the two stereoisomers on the preferential solvation and some other molecular parameters of the polymers. The extreme differences due to the structural effects between the stereoregular and the stereoirregular polymers appear in the mixed solvents with higher content of acetone.