Showing papers on "Membrane published in 1987"

Lipofection: a highly efficient, lipid-mediated DNA-transfection procedure

Abstract: A DNA-transfection protocol has been developed that makes use of a synthetic cationic lipid, N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA). Small unilamellar liposomes containing DOTMA interact spontaneously with DNA to form lipid-DNA complexes with 100% entrapment of the DNA, DOTMA facilitates fusion of the complex with the plasma membrane of tissue culture cells, resulting in both uptake and expression of the DNA. The technique is simple, highly reproducible, and effective for both transient and stable expression of transfected DNA. Depending upon the cell line, lipofection is from 5- to greater than 100-fold more effective than either the calcium phosphate or the DEAE-dextran transfection technique.

Hindered transport of large molecules in liquid‐filled pores

Abstract: Transport in liquid-filled pores of molecular dimensions plays an important role in membrane separations, in various forms of chromatography, and in catalysis, to name a few examples. A frequent observation is that if the pore dimensions are of the same order as those of a solute molecule, the apparent diffusion coefficient of that solute is much lower than in bulk solution. Likewise, rates of convective transport of such solutes are generally lower than the product of bulk concentration and volume flow rate. Thus, solute transport is typically “hindered” or restricted. A key objective of research on hindered transport is to be able to predict the applicable transport coefficients from such fundamental information as the size, shape, and electrical charge of the solutes and pores. The present status of this research is reviewed.

The light-harvesting and protective functions of carotenoids in photosynthetic membranes

Abstract: Siefermann-Harms, D. 1987. The light-harvesting and protective functions of carotenoids in photosynthetic membranes.

Water movement through lipid bilayers, pores, and plasma membranes

Abstract: THEORY: Osmotic Equilibrium Osmotic Transport (Osmosis) Induced by an Impermeant Solute Tracer Diffusion of Water Single-file Transport Osmotic Transport (Osmosis) LIPID BILAYER MEMBRANES: The Unmodified Membrane Nystatin an Amphotericin B. Gramicidin A PLASMA MEMBRANES: General Considerations The Red Cell Membrane Epithelia: Antidiuretic Hormone (ADH)-Induced Water Permeability Index.

Fluctuations in membranes with crystalline and hexatic order

Abstract: We study the interplay between crystalline (or hexatic) order and thermal fluctuations in membranes with vanishing surface tension. If the connectivity of the crystalline state is preserved, the membrane remains uncrumpled at low temperatures. When dislocations are allowed, however, screening of elastic stresses by buckling reduces dislocation energies, and promotes dislocation unbinding. When the resulting hexatic phase is stable, the stiffness associated with orientational correlations leads to a logarithmic enhancement of the bending rigidity which counteracts the thermal softening found in fluid surfaces. A finite temperature crumpling transition is predicted for crystalline membranes, and possibly for hexatic membranes as well.

[52] Preparation of high-purity plasma membranes

Abstract: Publisher Summary This chapter describes a method using the preparation of plasma membranes from light-grown oat ( Arena sativa L. ) leaves as an example. Using the batch procedure, two fractions containing purified plasma membrane (U 3 and U 3 , ) and one fraction containing intracellular membranes depleted of plasma membrane (L 1 ) are obtained. Specific staining with phosphotungstic acid or silicotungstic acid seems to be the only universal marker for the plant plasma membrane and the only one that permits a real estimation of the purity of the preparations. Based on this staining the purity is estimated to be higher than 90% and often close to 100%, plasma membrane and similar purities are reported for plasma membrane from maize roots. (>90%) for plasma membrane preparations obtained both by phase partitioning and free flow electrophoresis.

Structure-permeability relationships in silicone polymers

Abstract: Permeability coefficients P for He, O2, N2, CO2 CH4, C2H4, C2H6, and C3H8 in 12 different silicone polymer membranes were determined at 35.0°C and pressures up to 9 atm. Values of P for CO2, CH4, and C3H8 were also determined at 10.0 and 55.0°C. In addition, mean diffusion coefficients D and solubility coefficients S were obtained for CO2, CH4, and C3H8 in 6 silicone polymers at 10.0, 35.0, and 55.0°C. Substitution of increasingly bulkier functional groups in the side and backbone chains of silicone polymers results in a significant decrease in P for a given penetrant gas. This is due mainly to a decrease in D, whereas S decreases to a much lesser extent. Backbone substitutions appear to have a somewhat lesser effect in depressing P than equivalent side-chain substitutions. The selectivity of a silicone membrane for a gas A relative to a gas B, i.e., the permeability ratio P(A)/P(B), may increase or decrease as a result of such substitutions, but only if the substituted groups are sufficiently bulky. The selectivity of the more highly permeable silicone membranes is controlled by the ratio S(A)/S(B), whereas the selectivity of the less permeable membranes depends on both the ratios D(A)/D(B) and S(A)/S(B). The permeability as well as the selectivity of one silicone membrane toward CO2 were significantly enhanced by the substitution of a fluorine-containing side group that increased the solubility of CO2 in that polymer.

Water movement through lipid bilayers, pores, and plasma membranes : theory and reality

Abstract: THEORY: Osmotic Equilibrium Osmotic Transport (Osmosis) Induced by an Impermeant Solute Tracer Diffusion of Water Single-file Transport Osmotic Transport (Osmosis) LIPID BILAYER MEMBRANES: The Unmodified Membrane Nystatin an Amphotericin B. Gramicidin A PLASMA MEMBRANES: General Considerations The Red Cell Membrane Epithelia: Antidiuretic Hormone (ADH)-Induced Water Permeability Index.

Phosphorylation Fails to Activate Chloride Channels from Cystic Fibrosis Airway Cells

Abstract: Chloride impermeability of epithelial cells can account for many of the experimental and clinical manifestations of cystic fibrosis (CF)1,2. Activation of apical-membrane Cl− channels by cyclic AMP-mediated stimuli is defective in CF airway epithelial cells3,4, despite normal agonist-induced increases in cellular cAMP levels4,5. This defect in Cl− channel regulation has been localized to the apical membrane by exposing the cytoplasmic surface of excised membrane patches to the catalytic subunit (C subunit) of cAMP-dependent protein kinase and ATP. In membranes from normal cells, C-subunit activated Cl− channels with properties identical to those stimulated by cAMP-dependent agonists during cell-attached recording. Activation by the C subunit was not observed in CF membranes, but the presence of Cl− channels was verified by voltage-induced activation. The failure of the C subunit to activate the Cl− channels of CF membranes indicates that the block in their cAMP-mediated activation lies distal to induction of cAMP-dependent protein kinase activity and focuses our attention on the Cl− channel and its membrane-associated regulatory proteins as the probable site of the CF defect.

Dependence of junctional conductance on proton, calcium and magnesium ions in cardiac paired cells of guinea-pig.

Abstract: 1. The dependence of gap junctional conductance on the intracellular concentrations of H+, Ca2+ and Mg2+ was studied in paired myocytes dissociated enzymatically from guinea-pig ventricle. To apply an internal solution buffered to specific H+, Ca2+ or Mg2+ concentration directly to one aspect of the gap junction, the non-junctional membrane of one of the pair was mechanically ruptured. The junctional conductance was measured by clamping the membrane potential of the other cell using a two-pipette voltage-clamp method. 2. The conductance of the non-junctional membrane was kept low in comparison with that of the junctional membrane (less than 1/50) by replacing both external and internal K+ with Cs+. 3. The current-voltage (I-V) relation of the junctional conductance was linear over the potential range examined (from -100 to +100 mV). No voltage or time dependence was detected. 4. The conductance of the gap junction between the paired cells ranged from 90 to 3900 nS with a peak distribution at 1000 nS. 5. The effect of H+ was examined over the pH range 7.4-5.4, while keeping the free-Ca2+ concentration at zero, or pCa 6.3 or 7.0 using 2-10 mM-EGTA. The junctional conductance was almost constant from pH 7.4 to 6.5 and decreased in a dose-dependent manner with further acidification. There was no difference in the pH-conductance relationships at various Ca2+ concentrations. The Hill coefficient was approximately 2.4 and the half-maximum concentration (pK'H) was 6.1. 6. The closing effect of Ca2+ on the gap junction channel was examined over the concentration range from pCa 7 to 5, while keeping the pH at 7.4, 7.0 or 6.5. At each pH, increasing Ca2+ decreased the junctional conductance with similar Hill coefficients of about 3.4. The pCa-conductance relationship shifted toward a higher Ca2+ concentration range as the pH was lowered (pK'Ca = 6.6, 6.4 and 5.6, at pH 7.4, 7.0 and 6.5, respectively). 7. Increasing Mg2+ also caused a fall in the junctional conductance over the pMg range 3.0-2.0 with a pK'Mg of 2.5 (3.2 mM), and a Hill coefficient of 3.0. 8. These results suggest that there are two respective binding sites for divalent cations and H+, and that the gap junctional conductance is regulated reversibly by the ligand-receptor reactions. Comparing the threshold concentrations of Ca2+ and H+ for electrical uncoupling, it was concluded that Ca2+ plays a more important role in regulating the gap junctional conductance of cardiac cells under physiological conditions.

Erythrocyte membrane elasticity and viscosity.

Abstract: The classical theory of elasticity (35) treats the material of a deformable body as a three-dimensional continuum in which internal stresses occur as the body is deformed by external forces acting over its surface. Although the internal stresses are caused by the displacement of atoms or molecules from an original state of equilibrium, the molecular character of the material is ignored. This means that every volume element within the material must contain enough molecules to guarantee that the thermal fluctuation of anyone molecule does not effect the local state of stress. Since biomembranes in general and red cell membranes in particular are only a few molecules thick, they can form a continuum only in the plane of the membrane. Thus, the methods of classical, three-dimensional continuum mechanics must be compressed into a two-dimensional world in which "stress resultants" or "tensions" (force per unit width of membrane surface) are defined on the surface of the membrane (8, 25, 48). Measurement of the surface stress resultants and the corresponding surface deformations permits the material properties of the membrane surface to be calculated (15, 16, 20). These surface properties represent a summation, over the thickness of the membrane, of the properties of the lamellar, molecular structures that form the membrane.

Instability and deformation of a spherical vesicle by pressure.

Abstract: The infinitesimal stability of a spherical vesicle (closed membrane) is studied as a function of the pressure difference between the outer and inner media. It is found that above some threshold pressure the spherical vesicle can be deformed into a shape associated with $l\mathrm{th}$-order spherical harmonics. The comparison with numerical examples calculated previously by Deuling and Helfrich shows good agreement. Some applications to red blood cells are discussed.

Photomodification of biological membranes with emphasis on singlet oxygen mechanisms

Abstract: This review discusses photomodification of biological membranes and model membrane systems. Current concepts of membrane structure are first reviewed briefly. The role of preillumination association of sensitizer with membranes as it relates to photomodification rate is discussed, as well as the role of singlet oxygen in membrane photomodification. Finally the characteristics of singlet oxygen generation in membranes are considered. The evidence clearly indicates that membrane photomodification cannot be understood based only on the properties of sensitizers and singlet oxygen in aqueous solution. Rather the properties of sensitizers in association with membranes are the determinants of membrane photomodifcation. These properties differ significantly in aqueous solution and in membranes.

Lateral diffusion of proteins in membranes

Abstract: Membrane protein lateral diffusion can be constrained in several ways: Diffusion can be slower than that predicted for a simple, fluid lipid bilayer; diffusion can be confined to certain regions within the total membrane; and diffusion may not be equally probable in all directions, i.e. it may be anisotropic. We know that protein diffusion is reduced by increasing concentrations of membrane proteins and by interactions of the diffusant with structure(s) peripheral to the membrane. The molecular nature of such peripheral constraints has been difficult to pinpoint, but attention is now being directed to the extracellular matrix in addition to the membrane-associated cytoskeleton. There are many proteins that are confined to lateral domains in differentiated, isolated cells and in cells organized into tissue. The mechanisms that maintain such inhomogeneous distributions should be elucidated in the next few years. Whether lateral diffusion of membrane proteins over distances of a few micrometers is usually isotropic or anisotropic will be ascertained in the near future using imaging methods combined with photobleaching.

The Membranes of Cells

Abstract: The lipids of cell membranes membrane models and model membranes lipid properties in membranes cholesterol and cell membranes membrane proteins lipid-protein interactions and the roles of lipids in biological membranes transport membrane fusion membrane receptors the metabolism of membrane lipids membrane biogenesis.

Polyimide gas separation membranes

Abstract: Semi-flexible aromatic polyimides, prepared by polycondensation of dianhydrides with phenylene diamines having alkyl substituents on all ortho positions to the amine functions incorporating at least in part 3,3',4,4'-benzophenone tetracarboxylic dianhydride, are auto photochemically crosslinkable. Membranes formed from this class of crosslinked polyimides have improved environmental stability and superior gas selectivity than the corresponding uncrosslinked polyimide. The range of gas permeation properties observed allows for the tailoring of membrane material for widely diverse gas separations. The high permeabilities of some gases from multicomponent mixtures is due to the optimization of the molecular free volume in the polymer.

Structure of the novel membrane-coating material in proton-secreting epithelial cells and identification as an H+ATPase.

Abstract: Specialized proton-secreting cells known collectively as mitochondria-rich cells are found in a variety of transporting epithelia, including the kidney collecting duct (intercalated cells) and toad and turtle urinary bladders. These cells contain a population of characteristic tubulovesicles that are believed to be involved in the shuttling of proton pumps (H+ATPase) to and from the plasma membrane. These transporting vesicles have a dense, studlike material coating the cytoplasmic face of their limiting membranes and similar studs are also found beneath parts of the plasma membrane. We have recently shown that this membrane coat does not contain clathrin. The present study was performed to determine the structure of this coat in rapidly frozen and freeze-dried tissue, and to determine whether the coat contains a major membrane protein transported by these vesicles, a proton pumping H+ATPase. The structure of the coat was examined in proton-secreting, mitochondria-rich cells from toad urinary bladder epithelium by rapidly freezing portions of apical membrane and associated cytoplasm that were sheared away from the remainder of the cell using polylysine-coated coverslips. Regions of the underside of these apical membranes as large as 0.2 micron2 were decorated by studlike projections that were arranged into regular hexagonal arrays. Individual studs had a diameter of 9.5 nm and appeared to be composed of multiple subunits arranged around a central depression, possibly representing a channel. The studs had a density of approximately 16,800 per micron2 of membrane. Similar arrays of studs were also found on vesicles trapped in the residual band of cytoplasm that remained attached to the underside of the plasma membrane, but none were seen in adjacent granular cells. To determine whether these arrays of studs contained H+ATPase molecules, we examined a preparation of affinity-purified bovine medullary H+ATPase, using the same technique, after incorporation of the protein eluted from a monoclonal antibody affinity column into phospholipid liposomes. The affinity-purified protein was shown to be capable of ATP-dependent acidification. In such preparations, large paracrystalline arrays of studs identical in appearance to those seen in situ were found. The dimensions of the studs as well as the number per square micrometer of membrane were identical to those of toad bladder mitochondria-rich cells: 9.5 nm in diameter, 16,770 per micron2 of membrane.(ABSTRACT TRUNCATED AT 400 WORDS)