04 Fakultät Energie-, Verfahrens- und Biotechnik
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Item Open Access 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.Item Open Access 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.Item Open Access 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.Item Open Access Transduction of chemical signals in dictyostelium cells(1984) Gerisch, Günther; Tsiomenko, Arnold; Stadler, Joachim; Claviez, Michael; Hülser, Dieter F.; Rossier, ClaudeThree 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.Item Open Access 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.Item Open Access Patch-clamp measurements of gap-junction channels in cultured cells(1992) Hülser, Dieter F.; Eckert, Reiner; Zempel, Günther; Paschke, Dietmar; Dunina-Barkovskaja, AntoninaDirect intercellular communication in most tissues is made possible by proteinaceous pores called gap-junction channels. These channels bridge the extracellular gap between apposed cells and connect their intracellular compartments both electrically and metabolically. The extracellular parts of two hemichannels - the connexons - are linked thus forming a communicating gap-junction channel. A connexon is a hexamer of protein subunits which are members of the connexin family. Since connexin 32 (Cx32) was the first gap-junction channel protein to be sequenced from hepatocytes, it serves as a reference to which all other gap-junction proteins are compared. The individual channel conductance may vary between 25 and 150 pS. Gap-junction channels of some tissues are more voltage sensitive (e.g. liver) than others (e.g. heart). The question whether these differences in electrical properties may be attributed to the different connexins being expressed in these tissues is still unanswered. Several approaches to resolve this problem will be discussed in this contribution, all are based on double whole-cell patch-clamp measurements using isolated cell pairs, as follows: (1) Cells with two different channel conductances perfused with anti connexin antibodies to specifically block one channel species; (2) Cells with only one connexin species selected by immunological characterization; (3) Weakly coupled HeLa cells transfected with specific connexin genes, a method which resulted in better correlations between connexin type and single channel properties.Item Open Access Are biological effects of shock waves caused by free radicals?(1991) Suhr, Dierk; Brümmer, Franz; Hülser, Dieter F.Stone fragmentation in extracorporeal shock wave lithotripsy as well as accompanying tissue damage are attributed to cavitation. We attempted to demonstrate and localize the occurrence of cavitation in cell-free solutions and MGH-U1 cells using sensitive dyes for the detection of cavitation-generated free radicals.Item Open Access Shock waves and free radicals : cell protection by vitamin E in vitro and ex vivo(1993) Suhr, Dierk; Brümmer, Franz; Irmer, Ulrich; Schlachter, Manfred; Hülser, Dieter F.The application of extracorporeal generated shock waves in medicine for the fragmentation of human kidney and gall stones proved to be a very successful technique. Shock wave lithotripsy, however, is not free of tissue damaging side effects. One major mechanism for the fragmentation of stones as well as for the side effects is cavitation, ie. the formation and movement of bubbles in liquids exposed to tensile forces. Collapse of cavitation bubbIes is accompanied by local "hot spots" of several 1,000 K, thus generating free radicals. We investigated the contribution of these free radicals to cellular injury by varying the cellular amount of a well known scavenger of free radicals, α-tocopherol.Item Open Access Characterization of gap junctions by electrophysiological and electronmicroscopical methods(1990) Hülser, Dieter F.; Paschke, Dietmar; Brümmer, Franz; Eckert, ReinerGap junctions are ubiquitous in the animal kingdom from mesozoa to vertebrates. They must be discriminated from desmosomes which anchor cells together to form structural or functional units as well as from tight junctions which seal membranes of epithelial cells to each other so that the paracellular path becomes impermeable to molecules and a polarity of apical and basolateral surface is maintained.