Search PubMed⌕ Search

Biomedical subjects

S W Hui

Publications and source records attributed to S W Hui.

At least 145 records · Page 8Linked to original sources
PubMed1980

Effects of cholesterol on lipid organization in human erythrocyte membrane.

The molar ratio of cholesterol to phospholipid (C/P) in human erythrocyte membrane is modified by incubating the cells with liposomes of various C/P ratios. The observed increase in cell surface area may be accounted for by the addition of cholesterol molecules. Fusion between liposomes and cells or attachment of liposomes to cells is not a significant factor in the alteration of C/P ratio. Onset temperatures for lipid phase separation in modified membranes are measured by electron diffraction. The onset temperature increases with decreasing C/P ration from 2 degrees C at C/P = 0.95 to 20 degrees C at C/P = 0.5. Redistribution of intramembrane particles is observed in membranes freeze-quenched from temperatures below the onset temperature. The heterogeneous distribution of intramembrane particles below the onset temperature suggests phase separation of lipid, with concomitant segregation of intramembrane protein into domains, even in the presence of an intact spectrin network.

Cholesterol↗
PubMed1980

Cytoplasmic regulation of tight-junction permeability: effect of plant cytokinins.

The significance of the "leaky" tight junction might be understood better if cells of the epithelial monolayer possessed mechanisms to regulate molecular flow through the junction. To test this possibility, Necturus gallbladder, a representative leaky epithelium, was studied before, during, and after mucosal exposure to plant cytokinins and two other microfilament-active drugs, cytochalasin B and phalloidin. Concomitant with morphological changes in microfilaments, cytokinins induced rapid reversible increases in transepithelial resistance and potential difference (PD) and decreases in NaCl dilution potentials, with no change in the ratio of relative cell membrane resistances. Cytochalasin B (0.2-1.2 microM) and phalloidin (0.6-12.7 microM) caused similar changes in transepithelial resistance and PD. When the intramembranous structure of tight junctions was studied by freeze fracture, peak cytokinin-induced increments in transepithelial resistance were associated with more disorder in the strand meshwork resulting in a small increase in tight junction depth, but there was no evidence of de novo strand assembly. These studies suggest that permeability of the tight junction of Necturus gallbladder is subject to rapid reversible modulation, possibly under cytoskeletal control.

Animals↗
PubMed1979

Interactions of La3+ with phosphatidylserine vesicles. Binding, phase transition, leakage and fusion.

The interaction of La3+ with phosphatidylserine vesicles is elucidated by binding studies, differential scanning calorimetry, X-ray diffraction, freeze fracture electron microscopy, and release of vesicle contents. La3+ effectively competes with Ca2+ for phosphatidylserine binding sites. The saturation level is close to a La/lipid ratio of 1:3. A concentration of 0.1 mM of La3+ is sufficient to induce fusion between sonicated vesicles.

Calorimetry, Differential Scanning↗
PubMed1979

Selective decoration of hydrophilic moieties of membrane molecules in freeze fracture.

Selective decoration of the hydrophilic moieties of phospholipid molecules on freeze fractured bilayer faces was made using residue water vapor in an oil-free vacuum unit. The preferential decoration technique was applied to label structural faults of bilayers, such as domain boundaries and other regions of molecular dislocation which are not visible by conventional morphological observations.

Freeze Fracturing↗
PubMed1979

Correlative statistical analysis and computer modelling of intramembraneous particle distributions in human erythrocyte membranes.

The planar distribution of intramembranous particles on the P faces of freeze-fractured human erythrocyte membranes is characterized by radial distribution, angular distribution and differential density distribution analysis. Various degrees of intramembranous particle aggregation induced by spectrin removal and low pH are differentiated through computation. Random hard disk models with various disk diameters are built for comparison studies. In all samples, the 80 +/- 10 A particles are found to have a preferred neighboring distance of 100 +/- 10 A, but no preferred angular relation is found between neighboring particles. A pattern recognition process using both radial and density distribution analyses reveals that none of the particle distributions observed may be regarded as random. The fact that the particle distributions observed are neither even nor random suggests that factors other than long range electrostatic force alone are involved in determining the particle distribution.

Computers↗
PubMed1979

Complex phase mixing of phosphatidylcholine and phosphatidylserine in multilamellar membrane vesicles.

The phase mixing in dipalmitoyl phosphatidylcholine and bovine brain phosphatidylserine mixtures suspended in aqueous salt solutions was studied by differential scanning calorimetry, freeze-fracture electron microscopy and X-ray and electron diffraction. The pure dipalmitoyl phosphatidylcholine has two well-defined solidus phases P beta' and L beta' and a liquidus phase L alpha while the pure phosphatidylserine has a broad transition from L beta to L alpha. The mixture exhibits some dipalmitoyl phosphatidylcholine characteristics up to 30% phosphatidylserine when pure P beta' phase no longer exists. Phase mixing is observed at all compositions. An addition of 3% phosphatidylserine is found to be sufficient to destroy the sharp L beta'--P beta' transition observed in pure dipalmitoyl phosphatidylcholine. The transition between L beta' and P beta' in these mixtures is displaced to lower temperatures and becomes gradual as depicted by all three techniques, but freeze-fracture gives more definite information of the continuous transition. The most striking observation on the morphology of the mixed membranes (3--30% phosphatidylserine in dipalmitoyl phosphatidylcholine) is the presence of banded patterns (P beta') at temperatures well below the main transition peak as detected by differential scanning calorimetry.

Calorimetry, Differential Scanning↗
PubMed1979

Electron diffraction studies of human erythrocyte membrane and its lipid extracts. Effects of hydration, temperature and hydrolysis.

The organization of lipid molecules in individual human erythrocyte ghost membranes and single bilayers of their total lipid extracts were studied by low-dose electron diffraction in a controlled environment. The highest onset temperature (Ts) at which diffraction rings corresponding to a gel state appeared, were found to be in the range of -2 to -4 degrees C for both the whole ghost membrane and bilayers of its total lipid extracts. The onsets were abolished by dehydration before separated crystallizations of cholesterol and phospholipid occurred. Ts increased as a result of free fatty acids accumulation in membranes after phospholipase A2 treatment or storage.

Erythrocyte Membrane↗
PubMed1979

Topography and thickness of air-dried human platelets measured by correlative transmission and scanning electron microscopy.

Human platelets rapidly air-dried on carbon-coated grids were examined by transmission and scanning electron microscopy. Whole cell mounts were photographed in a transmission electron microscope (TEM), coated with gold, and then examined in a scanning electron microscope (SEM). The thickness of the cytoplasm towards the centre of the cells was estimated to be 20-40 nm, and the rim of dense material surrounding the cells was 40 nm thick. Some dense bodies stood out as much as 100 nm above the dried cytoplasm. These measurements are important for evaluating cytoplasmic volume during microprobe analyses of air-dried platelet preparations.

Air↗
PubMed1978

Fluorinated molecule as a tracer: difluoroserotonin in human platelets mapped by electron energy-loss spectroscopy.

The intracellular distribution of fluorine has been delineated in human platelets incubated with 4,6-difluoroserotonin, utilizing a scanning-transmission electron microscope equipped with an energy-loss spectrometer. Discrete intracellular structures corresponding in location to dense bodies contained high concentrations of fluorine. Electron energy-loss spectroscopy, which apparently can detect less than 10(-20) gram of fluorine in an area of 10 square nonometers, can thus localize fluorinated tracer molecules with biological activity.

Blood Platelets↗
PubMed1976

Hexagonal packing of lipid acyl chains and membrane plasticity.

Electron microscope and electron diffraction observations on microcrystals of pure lipids (a phosphatidylethanolamine, two phosphatidylcholines, a phosphatidic acid, and a galactocerebroside) reveal an extreme flexibility of lipid layers when the acyl chains are hexagonally packed (d100 = 4.17 A). This is corroborated by similar observations on wet bilayers of a lecithin. It is shown that more "crystalline" polymethylene packings do not impart such plasticity to lipid layers and are therefore an unsuitable structural matrix for dynamic biological membranes.

Cerebrosides↗
PubMed1976

The tilting of the hydrocarbon chains in a single bilayer of phospholipid.

The tilt angle of the hydrocarbon chains to the planes of a dipalmitoryl lecithin single bilayer and multilayers were estimated by the asymmetry of the electron diffraction patterns of respective hydrated specimens. The chains in a single bilayer were found to be perpendicular to the bilayer plane, whereas the chains in the multilayers were found to be tilted with respect to the normal of the plane. Thermal analysis data also supported this conclusion.

Binding Sites↗
PubMed1976

Direct observation of membrane movement by electron microscopy.

Motions of wet lipid bilayer membranes and plasma membranes of human erythrocytes were observed directly in an electron microscope, using the techniques of selective area diffraction, diffraction contrast imaging and electron opaque markers. The motions are measured as functions of temperature. At the liquidus state of the membrane, the lateral diffusion coefficient is deduced from the Brownian motion of the labeling particles. The coefficient is measured to be 1.1 x 10(-10) cm2/sec. for a bilayer of an equimolar mixture of cholesterol and dipalmitoylphosphatidylcholine at 20 degrees C. The value for human erythrocyte membrane at 37 degrees C is similar. At the temperature where phase separation occurs, motion is detected as the solidus domains floating on a liquidus medium. Below the transition temperature, the solidus domains move relative to one another along the domain boundaries, the drift velocity being 3 x 10(-6) cm/sec. for the above mentioned bilayer, at 4 degrees C. Together with specific labeling technique, the electron optical method may be used to study the movement of specific sites relative to the membrane, on a scale beyond the resolving power of light microscopy. The use of scanning electron microscopy is discussed.

Diffusion↗
PubMed1976

Phase transition of plasma membranes of rat hepatocyte and hepatoma cells by electron diffraction.

The transition temperatures (Tc) of the plasma membranes of Reuber H-35 hepatoma and normal ACl rat hepatocytes were measured by electron diffraction under physiological conditions. Diffraction rings below Tc indicate the existence of solid lipid domains. The Tc of both membranes increase to a plateau value of 17.5 degrees during the storage period of 4 days at 4 degrees, the rate of increase being slower for normal liver membranes. The extrapolations to zero storage suggest an innate difference of Tc for these two membranes. Storage in oxygen-reduced media slows down the initial increase in Tc in normal liver membranes, while the depletion of divalent cations accelerates the increase. Differences in lipid composition are partly responsible for this behavior.

Animals↗
PubMed1975

Direct observation of domains in wet lipid bilayers.

Domain structure and phase separation in hydrated lipid bilayers have been imaged directly by selected reflection dark-field electron microscopy. Domains in multicomponent bilayers are much smaller than those in single component bilayers, in agreement with results obtained by selected area electron diffraction.

Cholesterol↗
PubMed1975

Electron diffraction study of hydrated phospholipid single bilayers. Effects of temperature hydration and surface pressure of the "precursor" monolayer.

The molecular packing and phase transition of hydrated dipalmitoylphosphatidylcholine single bilayers are studied by electron diffraction, using an electron microscope equipped with a hydration stage. The phase transition and area per molecule are measured as functions of temperature, hydration and the surface pressure of the monolayer from which the bilayer is formed. The transition temperature of a bilayer agrees with calorimetric measurements on bulk lipid/water mixtures. The molecular packing of a bilayer corresponds to that of the precursor monolyer at a surface pressure of 47 dyne/cm.

Binding Sites↗