Biomedical subjects

H W Meyer

Publications and source records attributed to H W Meyer.

At least 19 recordsLinked to original sources

PubMed1995

The appearance of cytoplasmic membranes of Escherichia coli cells in freeze-fracture electron microscopy after stringent and relaxed response.

Guanosine-5'-diphosphate-3'-diphosphate (ppGpp), an effector for many metabolic pathways, is synthesized by the relA gene product after amino acid limitation. Studies of stringent controlled Escherichia coli CP78 (relA+) and relaxed controlled E. coli CP79 (relA-) were carried out to test whether these strains differ in the appearance of their cytoplasmic membranes after induction of stringent and relaxed response. Cytoplasmic membrane structures of the cells were investigated by freeze-fracture electron microscopy after cooling the cells. The obtained micrographs showed a net-like distribution of the particles in the cytoplasmic membranes of relaxed controlled cells whereas such a pattern was not detectable in the stringent controlled counterparts.

Amino Acids↗

PubMed1994

Convex-concave curvatures in bilayers of dipalmitoylphosphatidylcholine and cholesterol induced by amphotericin B/deoxycholate after prolonged storage.

Freeze-fracture investigations on the influence of amphotericin B/deoxycholate on multilamellar vesicles (MLV) of DPPC containing cholesterol have revealed a new phase structure. Alternating convex and concave curvatures are observed after storage of the vesicles at temperatures below 25 degrees C for at least 4 weeks. Three types of these patterns occur, a small-dimensional (repeat distance approximately 100 nm), an intermediate-dimensional (repeat distance approximately 400 nm) and a large-dimensional (repeat distance approximately 700 nm). The types can be formed on the same bilayer side by side. Additionally, the types differ in the morphology of the tops. In the case of the small-dimensional type the shape of the top can be described as a circular flat plane or opening and in the other cases as a hemispherical cap. The large dimensional type differs from the others by involvement of bilayer stacks. The formation of this new phase after prolonged storage could be confirmed by DSC measurements. The new structure can be explained in the framework of bicontinuous cubic phases and periodically curved bilayer structures. From the electron micrographs a lo (liquid ordered) phase is suggested.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1994

Is the brush border membrane of the intestinal mucosa a generator of "chymosomes"?

1. The microvilli of enterocytes in calf intestine demonstrate high levels of vesiculation activity at the top and at the basal region. 2. The morphology of the vesicles associated with microvilli (100-500 nm diameter, unilamellar, few intramembraneous particles, high AP activity) is very similar to the morphology of vesicles found in the chyme. 3. Vesicles can be purified 6-10 fold from chyme of the calf intestine applying a Mg(++)-precipitation method, used for brush border membrane preparation. 4. Specific activities of alkaline phosphatase and disaccharidases were found to be much higher in chyme vesicles than in the mucosa. 5. Phospholipid content and phospholipid composition is in chyme vesicles different from brush border membrane vesicles. 6. The characterized chyme vesicles are referred to as chymosomes. We consider the mucosa as a large-scale generator of chymosomes, i.e. digestive enzymes bearing vesicles.

Alkaline Phosphatase↗

PubMed1990

Membrane topology of microsomal cytochrome P-450: saturation transfer EPR and freeze-fracture electron microscopy studies.

The rotation of cytochrome P-450 LM2 (CYPIIB4) incorporated into large microsomal-like lipid vesicles was investigated by saturation transfer EPR using 15N- and 2H-substituted spin labels. In combination with rotational diffusion, the distribution and size of protein particles in the bilayer were studied by freeze-fracture electron microscopy. The data from both methods suggest an oligomeric and membrane-spanning aggregate for the topology of microsomal cytochrome P-450.

Cytochrome P-450 Enzyme System↗

PubMed1990

Periodically curved bilayer structures observed in hyphal cells or stable L-form cells of a Streptomyces strain, and in liposomes formed by the extracted lipids.

Periodically curved bilayer structures showing a tetragonal pattern were revealed by freeze-fracture electron microscopy in hyphal cells, stable L-form cells, and liposomes prepared from extracted lipids of Streptomyces hygroscopicus NG 33-354. The pattern is formed by alternating convex and concave curvatures of the bilayer. It has been found with different repeat distances (multiples of about 15 nm) and with a different degree of expression (from just visible to very pronounced). An interpretation as infinite periodic minimal surface (IPMS) structures is more probable than an inducement of the pattern by underlying small vesicles. The occurrence of nonbilayer textures and the similarity of the tetragonal pattern with a 'bilayer sector' from a cubic phase structure (Anderson, S. et al. (1988) Chem. Rev. 88, 221-242) support such an interpretation.

Cell Membrane↗

PubMed1990

[Does induced Heinz body formation lead to the liberation of IgG receptors on the erythrocyte membrane?].

Immunofluorescence microscopical and biochemical studies led other authors to the conclusion that the formation of membrane-bound Heinz bodies at these parts of the plasmalemma of erythrocytes leads to clustering of band 3-protein and increased binding of IgG. We failed to detect immunocytochemically an increased IgG binding over phenylhydrazine induced membrane-bound Heinz bodies in otherwise intact erythrocytes using transmission electronmicroscopy and we also did not notice any clustering of intramembraneous particles over the numerous Heinz bodies by means of freeze etching. Especially at higher phenylhydrazine concentrations the erythrocytes show formation of vesicles and hemolysis accompanied by increased IgG binding and clustering of the intramembraneous particles. Photographs of such cells obtained by immunofluorescence microscopy are very similar to the pictures known from the literature.

Anion Exchange Protein 1, Erythrocyte↗

PubMed1989

Hyperosmotic relaxation lysis of chromaffin granules is caused by interactions between the granular membrane and intragranular vesicles.

Bovine chromaffin granules undergo irreversible structural changes during osmotic shrinkage in hypertonic sucrose and salt solutions, such that, on reexposure to isoosmotic conditions they do not regain their original morphology, but undergo lysis ('hyperosmotic relaxation lysis'). Irreversible alterations of granules were induced by hypertonic incubations lasting for as little as 1 min. Fluorescence and EPR membrane labelling experiments showed that hypertonicity did not induce membrane loss for instance by inwardly or outwardly directed pinching off of membrane material. The mean sizes of chromaffin granules as a function of increasing and subsequently decreasing osmotic pressure were measured by photon correlation spectroscopy; there was no significant difference in sizes of hyperosmotically pretreated granules as compared with controls. Freeze-fracture electron micrographs showed the formation of 'twins' and 'triplets' under hypertonic conditions. They also revealed intragranular vesicles of 50-200 nm in diameter in both hypertonically and isotonically suspended granules. 'Twin' and 'triplet' granules were formed by the attachment of intragranular vesicles to the granule membranes. We suggest that hyperosmotic relaxation lysis is caused by the fact that this adhesion partly prevents the granule membrane from reexpanding, thus, leading to its rupture.

Animals↗

PubMed1989

[Extracorporeal shockwave lithotripsy in chronic pancreatitis].

Extracorporeal shock wave lithotripsy was performed on eight patients (six men, two women; mean age 46.3 years, range 36-58) with predominantly stone-induced obstructive pancreatitis. Stones in the pancreatic duct were smashed in one session to such an extent that the fragments were eliminated spontaneously via the ostium which had previously been split endoscopically. Repeat lithotripsy to achieve complete removal was necessary in only two patients. In one there were multiple concrements along the entire length of the main pancreatic duct; the other had a cherry-sized stone near the bifurcation of the accessory pancreatic duct. There were no serious complications. After successful removal of the stones all patients were free of pain which before had required strong analgesics to control. Six patients remained pain-free during a follow-up period of two eight months. Pain again occurred in the other two, but it was less frequent and milder.

Adult↗

PubMed1989

The influence of poly(ethylene glycol) on the molecular dynamics within the glycocalyx.

Interaction of polymers with cell surfaces is a question of general interest for cell aggregation and fusion. The molecular dynamics within the surface coat of human erythrocytes as well as alterations of membrane protein arrangement (IMPs) in the presence of poly(ethylene glycol) (PEG) were investigated by EPR spin labeling techniques and freeze-fracture electron microscopy, respectively. AT PEG concentrations which induce aggregation of erythrocytes the surface coat and the protein arrangement is not disturbed by the polymer. This implicate an exclusion of the polymer from the cell surface.

Cell Aggregation↗

PubMed1989

The phase diagram of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/sucrose in the dry state. Sucrose substitution for water in lamellar mesophases.

The phase diagram of the binary system, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/sucrose, was determined by DSC. In contrast to dry DPPC, which exhibits chain melting at 342.5 K, the main feature of the DPPC/sucrose system is eutectic melting at 320 K. This was supported earlier by Crowe, J.H., Crowe, L.M. and Chapman, D. (Science 223 (1984) 701-703), who reported a drastic decrease in the chain-melting temperature of the dry lipid in the presence of some mono- and disaccharides. Electron microscopy suggests that the phase structures on either side of the phase transition are of the lamellar type. Definite sugar saturation concentrations can be derived from this phase diagram. Up to about 17 mol% sucrose, i.e., 1 mol of sucrose per 5 mol of lipid is adopted by DPPC in the low-temperature phase Lc. In the high-temperature phase Lm the saturation concentration is well above 90 mol% sucrose at 320 K (eutectic point) but decreases with increasing temperature. The lower limit of 50 mol% sucrose is reached at 455 K. At this temperature, peritectic melting of sucrose occurs. Because of some similarities in the phase diagrams of DPPC/sucrose and DPPC/water, it is possible to understand the sucrose substitution for water in dry lamellar mesophases.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1988

Spatially periodic discrete contact regions in polylysine-induced erythrocyte-yeast adhesion.

Cell-cell adhesion occurs when human erythrocytes and yeast cells are suspended together in suprathreshold concentrations of polylysine in saline. The threshold polycation concentration for adhesion depends on cell concentration and decreases with increasing polycation molecular weight. The threshold concentration was similar for erythrocyte-erythrocyte adhesion and for yeast-erythrocyte adhesion. Transmission electron micrographs show that the erythrocytes adhere to yeast as if to engulf the cell. The regions of close contact between the erythrocyte membrane and the yeast cell walls are spatially discrete. The contact separation distance for the asymmetric erythrocyte-yeast adhesion is very similar to that (0.83 micron) observed when polylysine-induced adhesion occurs in the symmetrical erythrocyte-erythrocyte system. The spacing is attributed to the growth of a squeezing wave as an interfacial instability, on the intercellular aqueous layer. Freeze-fracture electron microscopy of cells that were not fixed during preparation for microscopy confirms the discrete nature of contacts between polylysine treated erythrocytes.

Cell Adhesion↗

PubMed1988

Effect of proteases and other treatments on the proliferative assembly of tight junction strands in the rat prostate tissue.

As already observed with the freeze-fracture technique by Kachar and Pinto da Silva (1981) incubation of excised rat ventral prostate tissue at 37 degrees C results in proliferation of tight junction strands over the lateral membranes of the epithelial cells, an effect not occurring after incubation at 4 degrees C. Our investigations have shown that a pretreatment with protease inhibitor Contrykal at 4 degrees C suppresses the proliferation of tight junction strands at 37 degrees C. On the other hand the added proteases trypsin and pronase induce the proliferation already at 4 degrees C. The effect was lowered by higher concentrations of pronase. Incubation with solutions of the non-ionic detergent Triton X-100 at 4 degrees C could also induce tight junction proliferation, whereas this effect was nearly absent after an incubation at 4 degrees C with a hyperosmotic solution of arabinose and with 50% acetone. No relation was found between proliferation of tight junction strands and cluster formation of intramembraneous particles. In conclusion of the results a small protein or a peptide resembling fusions proteins is assumed as trigger for formation of tight junction strands, acting by destabilization of the bilayer arrangement of membrane lipids.

Acetone↗

PubMed1988

Freeze-fracture investigations of membranes of flask cells in the kidney and of parietal cells in the stomach of claw-frog (Xenopus laevis).

The flask cells of the nephron and the parietal cells in the stomach fundic glands of claw-frog show some structural similarities such as the existence of a canalicular system, the richness of mitochondria and numerous small cytoplasmatic vesicles. Both cell types also seem to have common functional pecularities. With the freeze-fracture method the cell membranes of both cell types showed a richness of intramembrane particles (IMPs) and the existence of special elongated IMPs especially in the apical and canalicular cell membranes. In the flask cells the elongated so-called rod-shaped IMPs measured 29 X 13 nm and were very numerous, whereas the corresponding particles in the parietal cells in the same membranes were smaller (13 X 5 nm) and not so numerous. The similarities and differences between the membranes of both cell types are discussed in relation to the cell function.

Acid-Base Equilibrium↗

PubMed1988

Preparation and properties of large octylglucoside dialysis/adsorption liposomes.

The suitability and capacity of the polystyrene resin Wofatit EP 60 for the adsorption of octylglucoside, Triton X-100, Cholate, and CHAPS was studied. Optimal detergent/bead ratios and the maximum capacity of Wofatit EP 60 for the four detergents were determined as prerequisites for optimal application of the beads in liposome preparations. It is shown that large unilamellar liposomes can be prepared easily, quickly and cost-effectively using a combined dialysis/adsorption method with octylglucoside as detergent and Wofatit EP 60 and adsorbing polystyrene beads. Structure, composition, size, homogeneity, lamellarity, stability, internal volume, and residual octylglucoside concentration were studied by gel chromatography, radioactive assay, dynamic light scattering and electron microscopy. Vesicle size and homogeneity depend on lipid concentration, lipid composition, cholesterol content, and the rate of octylglucoside removal, but not on the detergent/lipid ratio. The reliability of the method and the properties of the vesicles are compared with those of other methods and researchers.

Adsorption↗

PubMed1987

Membrane skeleton alteration--a factor promoting IgG receptor expression in the erythrocyte membrane.

IgG receptor expression after selective cross-linking of spectrin by means of diamide was investigated. A diamide concentration dependent IgG loading of erythrocytes was observed. Furthermore, diamide causes disturbance of lipid asymmetry, decrease of the anisotropy after topooptical staining of the glycocalyx, increase of the phagocytosis index and aggregation of the IMP's. Our findings support the hypothesis that the arrangement of the membrane skeleton at the inner aspect of the membrane is decisive not only for the lipid asymmetry but also for the spatial structure of the glycocalyx at the outer aspect of the membrane and thus for the degree of exposure and arrangement of IgG-receptors, which are thought to be localized at an extracellular portion of band 3 protein.

Anion Exchange Protein 1, Erythrocyte↗

PubMed1986

[Characterization of vasopressin receptors in cerebral endothelial cells].

In target cells with receptors of the V2 type, vasopressin activates the adenylate cyclase and induces, finally, a clustering of intramembranous particles in the plasma membrane. Both characteristic effects, however, could not be observed at hippocampal capillaries of the rat. The presumed vasopressin receptors at cerebral capillaries that represent the blood-brain barrier are, therefore, probably not of the V2 type.

Animals↗

PubMed1986

Structures of liposome membranes as models for similar features of cytoplasmic membranes of bacteria.

To characterize a special kind of membrane structure, visible in the cytoplasmic membranes of a Streptomyces hygroscopicus strain, liposome membranes were prepared from their extracted lipid mixture and from their lipid fractions (phospholipids, glycolipids, neutral lipids) and investigated by freeze-fracture electron microscopy. Liposome membranes made of the extracted lipid mixture reveal this special membrane structure, named wafer structure, from its regular pattern of bulges (30-40 nm in diameter). That is the proof that this membrane feature is a lipid structure. Liposome membranes prepared from the lipid fractions show the wafer structure if they are made of the phospholipid fraction only or in combination of this fraction with one or both of the other lipid fractions, indicating that wafer structure formation is primarily connected with the phospholipid content of the membranes. The glycolipid- and neutral lipid fractions amplify this phospholipid structure only. Additional to the wafer structure a raspberry structure with bulges of 55-65 nm in diameter is visible in some case. Obviously both structures are related.

Cell Membrane↗

PubMed1984

Incorporation of the cytochrome P-450 monooxygenase system into large unilamellar liposomes using octylglucoside, especially for measurements of protein diffusion in membranes.

Cytochrome P-450 and NADPH cytochrome P-450 reductase were incorporated into large unilamellar lipid vesicles (200-300 nm in diameter) removing octylglucoside from mixed micelles by dialysis. The large size of the protein-containing liposomes guarantees a negligibly small vesicle tumbling. Such large vesicles are better suited for studies of protein rotation in reconstituted membranes than vesicles prepared by use of bile salts. At present the octyl-glucoside reconstituted monooxygenase system seems to be the most appropriate model for studying protein-protein and protein-lipid interactions in liver microsomes due to the similarity with respect to the main structural and functional properties, including size.

Animals↗