PubMed Health⌕ Search

Biomedical subjects

D Frösch

Publications and source records attributed to D Frösch.

At least 19 recordsLinked to original sources
PubMed1989

New techniques of analyzing the healing process of artificial vascular grafts, transmural vascularization, and endothelialization.

Beside traditional techniques (light, immunofluorescence, transmission electron (TEM)- and scanning electron microscopy (SEM), a new more sensitive method for producing microcorrosion casts using a polyester-based resin has been developed. The SEM analyses of the microcorrosion casts of alloplastic vascular grafts was realized in an absolutely stable stage of polymerization. For the first time, a transprosthetic vascularization could be shown in great three-dimensional detail. The importance of a complete and rapid endothelialization of artificial vascular grafts is discussed.

Animals↗
PubMed1989

Melamine resins and their application in electron microscopy.

Melamine resins are derived from the heterocyclic compound triaminotriazine, C3H6N6. Similar to proteins in structure and reactivity, water-soluble melamine resins can be used as water-embedding media for electron microscopy (Bachhuber and Frösch, 1983). The idea behind this approach was to study some of the artefacts of traditional embedding techniques and to work out conditions to eliminate as far as possible denaturing of proteins and extraction of lipids. Sectioned cells and tissues processed in the melamine resin Nanoplast show remarkable preservation of ultrastructure. Because they can be sectioned extremely thinly, melamine resins are particularly suitable for dark-field and electron spectroscopic imaging of unstained molecular suspensions providing in this way an unusually clear reproduction of ultrastructural detail such as the helical structure of isolated unstained double-strand DNA molecules (Frösch et al., 1987b). In 1988, the melamine resin Nanostrat was introduced as an EM-compatible prolific substrate foil for cell culture (Westphal et al., 1988). Cells or bacteria cultivated on this material can be processed for various kinds of follow-up techniques like TEM, SEM, vertical sectioning and immunocytochemistry.

Animals↗
PubMed1989

New observations on the healing process in prosthetic substitution of large veins by microporous grafts--animal experiments.

Based on the experimental experiences in more than 180 implantations of different materials as venous substitutes segments of the inferior vena cava have been replaced in 34 dogs by Polyurethane (low microporosity) and modified e-PTFE prostheses (increased microporosity of 60 microns and 90 microns fibril length). The 12 months patency rate didn't differ between both tested optimized materials and ranged from 43 to 50%. After a follow-up of 12 months the grafts were taken out and analysed by light, immunofluorescence microscopy, scanning and transmission electron microscopy. In addition a new technique of microcorrosion casts was used for SEM-analyses. As a result a transmural microvessel system in the microporous meshwork of the prostheses with multiple orifices at the inner surface of the grafts could be demonstrated. Complete endothelialization was only observed in e-PTFE prostheses of high microporosity (greater than 60 microns fiber length). There is strong evidence that a full tissue incorporation of microporous artificial grafts mainly depends on a sufficient primary intramural deposit of blood components (fibrin, platelets, leucocytes), which initiates cell invasion from the surrounding tissue, accompanied by a highly developed microvessel network. A multifocal endothelialization takes place from the numerous microvascular orifices on the inner surface of the prostheses. Other sources such as pannus invasion or adhesion of multipotent cells from the blood stream play probably a very limited role.

Animals↗
PubMed1989

Integrin VLA-3: ultrastructural localization at cell-cell contact sites of human cell cultures.

The integrin VLA-3 is a cell surface receptor, which binds to fibronectin, laminin, collagen type I and VI (Takada, Y., E. A. Wayner, W. G. Carter, and M. E. Hemler. 1988. J. Cell. Biochem. 37:385-393) and is highly expressed in substrate adherent cultures of almost all human cell types. The ligand specificity of VLA-3 and the inhibition of cell adhesion by anti-VLA-3 monoclonal antibodies suggest its involvement in cell-substrate interaction. In normal tissues, VLA-3 is restricted to few cell types, notably the kidney glomeruli and basal cells of the epidermis. In the epidermis, VLA-3 is generally strongly expressed on the entire plasma membrane of basal cells and is not polarized towards the basement membrane (Klein, C. E., C. Cardon-Cardo, R. Soehnchen, R. J. Cote, H. F. Oettgen, M. Eisinger, and L. J. Old. 1987. J. Invest. Dermatol. 89:500-507). Based on this finding we speculated that, in addition to a role of VLA-3 for adhesion of cells to substrate, it could also be relevant for cell-cell interaction. To investigate this, we ultrastructurally localized VLA-3 on the surface of cultured cells by immunoelectron microscopy. In accordance with our concept, we found VLA-3 strongly associated with intercellular contact sites. Interestingly, very little immunoreactivity was detected at the under-surface of cells which had been cultured for 18-32 h. This observation was unexpected but is consistent with previous findings (Kantor, R. R. S., M. J. Mattes, K. D. Lloyd, L. J. Old, and A. P. Albino. 1987. J. Biol. Chem. 262:15158-15165) which suggest that the association of VLA-3 with the basal surface of substrate adherent tumor cells is a late event occurring after days of culture under confluent conditions. However, we cannot formally rule out VLA-3 expression at the undersurface of cells under our experimental conditions, since VLA-3 molecules at this location could be inaccessible for in situ labeling of unfixed cells because of spatial interferences. In conclusion, our results demonstrate the expression of VLA-3 at intercellular contact sites of cultured cells supporting the concept that it may be relevant for intercellular interactions also.

Animals↗
PubMed1989

Ultrastructure of the contractile apparatus of rat skeletal muscle embedded in an aqueous medium.

The method of tissue embedding in melamine resin was applied to rat skeletal muscle. This method does not require tissue dehydration with organic solvents; only aqueous solutions are used. Electron micrographs of muscles embedded in melamine differ from those embedded in the conventional epoxy resin. In melamine-embedded muscles the actin and myosin filaments appear larger in diameter and subunits can be recognized in cross-sectioned myosin filaments. Within the Z-line, the characteristic patterns described for muscles embedded in epoxy resin are not visible; the spaces between the actin filaments are filled with electron-dense material. This suggests that the Z-line is more compact than could be concluded from epoxy resin-embedded muscle specimens. The M-line appears to be different from what is observed in epoxy-embedded muscle. The membranes appear as several clearly delineated layers. Dehydration rather than the action of the organic solvents per se is the main reason for the differences in the structure of the contractile apparatus between melamine- and epoxy-embedded muscles.

Actin Cytoskeleton↗
PubMed1988

A new method for cell culture on an electron-transparent melamine foil suitable for successive LM, TEM and SEM studies of whole cells.

A new cell culture technique is described which is based on the observation that foils cast from the melamine resin hexamethylol-melamine-ether are suitable for the cultivation of beating heart muscle cells and fibroblasts of the rat. This foil can be flamed for sterilization, is about 80 nm in thickness, homogeneous and smooth, withstands dehydration and critical point-drying, can be removed from glass and permits the imaging of whole cells successively by light microscopy, transmission and scanning electron microscopy. The method is capable of narrowing the gap between light and electron microscopy, yielding excellent whole cell preparations in various kinds of microscopic studies to be performed on one and the same cell.

Animals↗
PubMed1987

Dark-field electron microscopy of unstained biological materials embedded in Nanoplast.

Extremely thin sections of unstained materials (beef liver catalase, double-stranded calf thymus DNA, horse spleen ferritin and mammalian skeletal muscle), embedded in the water-soluble melamine resin Nanoplast FB101, were studied by dark-field electron microscopy and electron spectroscopic imaging. While ferritin molecules so recorded show 0.4 and 0.9 nm lattice fringes within the crystalline iron core, double-stranded DNA shows a helical repeat with a spacing of 3.4 nm. The gain in resolution of structural detail reported here is probably due mainly to the reduced section thickness as compared to traditional thin-sectioning techniques. As we reported earlier (Frösch & Westphal, 1984), melamine resins can be sectioned extremely thinly (less than 10 nm) and observed without a supporting film, making them especially suitable for dark-field electron microscopy.

Animals↗
PubMed1985

A determination of thickness and surface relief in reembedded sections of an epoxy- and a melamine-resin containing ferritin as size standard.

Chemical and physical data of two electron microscopic embedding media (the non-polar epoxy resin Epon 812 and the polar melamine resin Nanoplast FB 101) suggest that less kinetic energy must be applied for cutting a section from a Nanoplast block than from an Epon block of the same hardness and that, consequently, the cutting qualities of Nanoplast are better. To test this hypothesis, normal and extremely thin sections of Epon- and Nanoplast-embedded horse spleen ferritin micropellets were reembedded and resectioned for a determination of thickness and surface roughness. The ease with which extremely thin sections can be cut from the Nanoplast resin (8 nm versus 15 nm in Epon) and the smooth surface of these sections support the hypothesis that the cutting quality of an embedding material is determined primarily by its energy balance, i.e. by the kinetic energy which must be introduced for sectioning and the bonding energy which is released exothermically from a polymer while being sectioned.

Animals↗
PubMed1985

Fracturing of melamine-embedded cells and tissues: a new technique for studying cell membranes.

A new technique is presented for studying cell membranes by scanning electron microscopy. It is based on the observation that cells and tissues, embedded in a water-compatible melamine resin, are as hard as glass and consequently can be fractured with ease. Fracture faces so exposed are either sputter-coated for studying the surface topography or re-embedded for thin-sectioning, or both. Scanning electron microscopy shows that the fracture faces of a variety of tissues reveal cell membranes and associated structures with remarkable detail. Re-embedding and thin-sectioning of fractured frog retina, mycoplasma and red blood cells indicate that membranes become divided into their exo- and protoplasmic leaflets during fracturing. In this respect, the results reported here must be compared with conventional freeze-fracture techniques.

Acholeplasma laidlawii↗
PubMed1985

Choosing the appropriate section thickness in the melamine embedding technique.

When biological materials are infiltrated by a water-soluble melamine resin and hardened, they become as hard as glass. This is a prerequisite for extreme thin-sectioning. In this paper, the structural information from unsupported transparent thin sections of beef liver catalase, calf thymus DNA, horse spleen ferritin, insect muscle and rat microtubules is compared to that of normal thin sections. While ferritin molecules (12 nm diameter), microtubule subunits (8 nm long axis) and catalase crystals (8 nm subunit diameter) appear to become mechanically damaged in a 10 nm section (as measured by resectioning), DNA-molecules (3 nm diameter) are satisfactorily preserved during sectioning. Remarkably, for electron phase contrast imaging of unstained cross-sectioned insect muscle, a minimum section thickness of about 30-40 nm is required.

Animals↗
PubMed1982

Lateral mobility of membrane-bound antibodies on the surface of Acholeplasma laidlawii: evidence for virus-induced cell fusion in a procaryote.

Dynamic processes on the membrane of the procaryotic cell Acholeplasma laidlawii have been studied by means of immunoelectron microscopy. Colloidal gold-labeled anti-A. laidlawii antibodies were used as electron-dense markers. This method allowed the demonstration of temperature-dependent lateral mobility of membrane-bound immunoglobulins. By using two different sizes of gold grains to differentiate cells from two different cell populations, virus-induced fusion of procaryotic cells could be shown for the first time.

Acholeplasma laidlawii↗
PubMed1981

Enkephalin-related peptides: direct action on the octopus heart.

Immunocytochemical evidence for the occurrence of "vertebrate" peptides in the neuropil of the vena cava [12, 13] and the structural similarity between enkephalin precursor peptides and the molluscan cardioexcitatory peptide [16], lead us to study the action of enkephalin-related peptides on the octopus heart. Systemic hearts of Octopus vulgaris were perfused with sea wate and test substances and a crude extract of vena cave were added for 1 min; frequency and pressure were monitored continuously. The heptapeptide Leu5-enkephalin-Arg6-Phe7 and the Met5-analogue, both in the amidized form, displayed dose-response relationship with a sensitivity of about 10 nmol. The C-terminal tetrapeptide amides, Phe-Leu/Met-Arg-Phe-NH2, were active at the same doses. Opiate receptors do not seem to be involved in this action on the octopus heart, as naloxone treatment had no effect. Whereas the N-terminal portion of the heptapeptide is known to be crucial for activity as an opioid, the C-terminal NH2 group is essential for cardioexcitatory activity.

Animals↗