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Publication Type: search.filters.UBSTyp.KonferenzbeitragSubject: search.filters.subject.570

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    Biophysical investigations of the in vitro effects of shock waves and ultrasound
    (1993) Brümmer, Franz; Suhr, Dierk; Irmer, Ulrich; Bachleitner, Christoph; Hülser, Dieter F.
    To investigate the interactions of ultrasonic waves with biological tissues, we developed and standardized several in vitro models. Using these systems - artificial stones, human erythrocytes, L1210 mouse leukemia cells, multicellular spheroids, cavitation assay - we are able to elucidate the mechanisms of interaction as well as the cause of clinically observed side effects.
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    Extraordinary biological membrane structures resulting from different local membrane curvatures
    (1992) Meyer, Helmut W.; Hülser, Dieter F.
    The bilayer arrangement of amphiphilic molecules is not only the basic structure of rather flat biological membranes, but also of regularly curved bilayers in most cubic phase structures. The basis of these cubic phase structures are infinite periodical minimal surfaces (IPMS). Extraordinary biological membrane structures resembling such IPMS were found as periodically curved bilayers in areas of the plasma membrane in a Streptomyces strain and in liposomes prepared from its extracted lipids. This structure consists of a transition of convex to concave curvatures and vice versa. A structure with curvatures in one direction only was observed in vacuolar membranes of yeast cells with a genetic defect. Our electron microscopical analysis of freeze fractured membranes of these cells revealed not only fully invaginated but also flat particle-free areas which were mainly circularly shaped, some elongated areas, however, were also present. In addition, sometimes periodical arrangements were detected which obviously are not related to IPMS structures. Both structures, however, indicate a high proportion of wedge-shaped lipid molecules in the bilayer.
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    β-galactosidase production in two- and threedimensionally cultivated cell cultures
    (1991) Klünder, Irene; Hülser, Dieter F.
    In these studies, we demonstrate that the threedimensional arrangement of the cells in spheroids influences the β-galactosidase activity of transfected ltk--cells. In contrast to cells grown in monolayer culture cells growing as spheroids lost their β-galactosidase activity within few days. The reduction of β-galactosidase activity in cells grown as spheroids was not caused by a lost of the lacZ-gene as can be seen from the recovery of the β-galactosidase production when cells were retransferred in monolayer culture. As we showed in cells cultivated as monolayer, β-galactosidase activity seems to be not impaired by gradients of nutrient supply or cell cycle. These measurements are confirmed by histological sections, where the highest β-galactosidase activity was found in the viable center of the spheroids.
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    Transduction of chemical signals in dictyostelium cells
    (1984) Gerisch, Günther; Tsiomenko, Arnold; Stadler, Joachim; Claviez, Michael; Hülser, Dieter F.; Rossier, Claude
    Three different functions of cyclic AMP in D discoideum are known: (1) cAMP acts as a chemoattractant during cell aggregation, (2) it controls cell development, particularly the acquisition of aggregation competence, and (3) it is involved in terminal cell differentiation. In this report we will concentrate on the functions 1 and 2 of cAMP. Chemotaxis requires the recognition of concentration gradients in the environment by attractant binding to cell surface receptors, the processing of signals from the receptors to the contractile system of the cells, extension of pseudopods at one part, and contraction at other parts of the cells in accord with the external gradient. One pathway of signal processing from the receptors to the contractile system involves the regulation of a myosin kinase. The control of development up to aggregation competence is largely dependent on the temporal pattern of cAMP application: Only repetitive pulses enhance development. This effect has been studied using the expression of a membrane glycoprotein called contact site A as a differentiation marker.
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    Cyclic-AMP reception and cell recognition in dictyostelium discoideum
    (1975) Gerisch, Günther; Malchow, Dieter; Huesgen, Adolfine; Nanjundiah, Vidyanand; Roos, Werner; Wick, Ursula; Hülser, Dieter F.
    Single cells of the slime mold, Dictyostelium discoideum, aggregate into a multicellular organism in response to cyclic AMP, which they detect by binding to cellsurface receptors. During the aggregation phase, two different responses to cyclic-AMP are observed. First, the cells orientate by chemotaxis towards the source of a concentration gradient which initially is a group of cells forming an aggregation center. Second, the cells relay pulses which are periodically generated by the centers.
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    Pulsed high-power-sonication of concrements, cancer cells and rodent-tumors in vivo
    (1989) Riedlinger, Rainer E.; Brümmer, Franz; Hülser, Dieter F.
    Extracorporeal lithotripsy has been successfully established, based on different principles of generating and focusing the shock waves. Lithotripters have also been used to investigate the influence of shocks to cancer cells and solid tumors. With two different trans-mitters (spark-gap type XL-1 and piezo-resonance type MW 2) we applied shock waves and short high power US-pulses to suspended and immobilized tumor cells and multicell spheroids. With MW 2 significant local damage on cell spheroids in gelatin was achieved, caused by locally controlled cavitation. The results are compared to each other.
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    Nervous-system-specific carcinogenesis by ethylnitrosourea in the rat: molecular and cellular aspects
    (1977) Rajewsky, Manfred F.; Augenlicht, Leonard H.; Biessmann, Harald; Goth, Regine; Hülser, Dieter F.; Laerum, Ole D.; Lomakina, L. Ya.
    A lead in the search for cellular determinants favoring neoplastic transformation may be provided by the pronounced tissue specificity of the oncogenic effect of certain carcinogens which do not require enzymatic metabolic activation, i.e., in cases where this specificity cannot be due to tissue differences in the activity of enzymes involved in the formation of the ultimate reactants. A carcinogen that fulfills this condition is the ethylating agent N-ethyl-N-nitrosourea (EtNU). Alkylation of nucleic acid constituents by N-nitroso compounds in relation to mutagenesis and carcinogenesis has received considerable attention recently.
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    Molecular and cellular mechanisms in nervous system-specific carcinogenesis by N-ethyl-N-nitrosourea
    (1976) Rajewsky, Manfred F.; Goth, Regine; Laerum, Ole D.; Biessmann, Harald; Hülser, Dieter F.
    A single pulse of N-ethyl-N-nitrosourea (ENU), applied to BDIX rats during the perinatal age, specifically results in a high incidence of neuroectodermal neoplasms in the central and peripheral nervous system (NS). The pronounced sensitivity of the developing NS suggests a dependence of the carcinogenic effect on the proliferative and/or differentiative state of the target cells at the time of the ENU pulse. The specificity of ENU for the NS cannot be due to tissue variations in the degree of carcinogen-cell interactions, since the reactive, electrophilic ethyl cation is produced by rapid, nonenzymatic decomposition of ENU indiscriminately in all tissues. Correspondingly, the initial molar fractions of ethylated purine bases are similar in the DNA of "high-risk" (perinatal brain) and "low-risk" tissues (e.g., liver; adult brain). However, while the respective half lives in DNA of N7-ethylguanine and N3-ethyladenine show only minor differences for both types of tissues, the mutagenic ethylation product 06-ethylguanine is removed from brain DNA very much more slowly than from the DNA of other tissues. Together with their high rate of DNA replication during the perinatal age, the incapacity of rat brain cells for enzymatic elimination of 06-alkylguanine from their DNA could account for an increased probability of neoplastic conversion, and hence for the NS specificity of ENU in the rat.
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    Production of tissue plasminogen activator (t-PA) with differentiated F9-embryonic carcinoma cells grown as multicell spheroids
    (1991) Brenner, Joachim; Zempel, Günther; Hülser, Dieter F.
    F9 cells can only temporarily be cultivated as single cell suspension. The growth of multicell spheroids from a single cell suspension is shown. Within 24 hours the cells aggregated to multicell spheroids in spinner flasks. The aggregation was almost finished within 24 h and was independent of the initial cell concentration. but could be influenced by the geometry of the cultu re flask and the stirring velocity. A significant cell proliferation of the anchorage-dependent F9 cells was only detectable in the aggregated state. A narrow size distribution of multicell spheroids in a 3 days old culture revealed identical spheroid sizes. Under our conditions. with an inital cell density of 10 5 cells/ml a cell concentration of 6x10 6 cells/ml was reached within 4 days of spheroid culture. Cells in monolayers and in multicell spheroids were well coupled by gap junctions. Differentiated F9 cells showed a fibroblastoid morphology in contrast to the epitheloid morphology of undifferentiated F9 stem cells. This was not the case for multicell spheroids where the cells were also well coupled.
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    Simultaneous degradation of chloro- and methylaromatics via ortho pathway by genetically engineered bacteria and natural soil isolates
    (1989) Engesser, Karl-Heinrich; Pieper, Dietmar H.; Rojo, Fernando; Timmis, Kenneth N.; Knackmuss, Hans-Joachim
    The simultaneous bacterial metabolism of chloro- and methylaromatics via ortho- or metapathway, normally results in incomplete degradation and death of the organisms. This is caused by misrouting of central intermediates. i.e. substituted catechols into unproductive pathways and suicide inactivation of the key enzyme of meta pathway, (catechol 2,3-dioxygenase). The meta pathway proved to be definitely unsuited for productive metabolism of chloroaromatics. Therefore two strategies were used for simultaneous degradation of mixtures of chloro- and methylaromatics via ortho pathways: Methyllactons or certain mixtures of chloro- and methylaromatics were used as enrichment substrates, yielding strains which metabolized these compounds almost exclusively via the desired pathway. Alternatively relevant enzymes from five different catabolic pathways of three distinct soil bacteria were combined in a patchwork fashion generating a functional ortho cleavage route for methylaromatics coexisting with the ortho cleavage pathway of chloroaromatics.