04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
Browse
98 results
Search Results
Item Open Access Probleme der Gestaltbildung(1990) Kull, UlrichDie Einzelheiten der Bildung komplexer Gestalten von Lebewesen können nicht vollständig genetisch fixiert sein, da hierzu die Zahl der Gene der Organismen kaum ausreichen würde. Es muß also Vorgänge der Gestaltbildung geben, die auf grund weniger genetischer Festlegungen (Randbedingungen} unter Selbstorganisation ablaufen; sie sind "systemimmanente Eigenschaften". Ein besonderes schönes Beispiel dafür liefern die Radiolarien, die schon Haeckel der ästhetisch ansprechenden Skelettformen wegen sehr schätzte.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 Biological effects of shock waves(1990) Brümmer, Franz; Bräuner, Thomas; Hülser, Dieter F.Extracorporeal shock wave lithotripsy has become established worldwide as the method of choice for the treatment of nephrolithiasis and ureterolithiasis over the last 10 years. Although initial studies showed no damaging effects of the shock waves on organs and tissues, numerous recent reports have presented evidence for severe acute effects and chronic complications after shock wave treatment. The pathophysiological effects on kidneys and the histopathological effects on organs or tissues in man and animal, and also the effects on cells in culture and tumors are sumarized. Suspended and immobilized cell cultures were used to characterize and quantify the efficacy of shock wave. Extended applications of shock waves and possible modifications to shock wave generators are discussed.Item Open Access Introduction - Symposium on Intercellular Communication Stuttgart, 1982(1982) Hülser, Dieter F.Intercellular communication is a postulate of complex multicellular organisation. Signal transfer between cells is possible in different ways: 1.) Long distances of up to 1 m may be bridged by molecules which are produced in distinct cells and are released into the extracellular fluid where they are distributed and interact with receptors on the surface of their target cells (e.g., humoral interaction). 2.) Transmitter substances which have a limited life span or which can be inactivated by inhibitor molecules spread signals only over shorter distances (e.g., synaptic cleft, -200nm). 3.) Information can also be exchanged by direct membrane contact when two molecules interact with each other directly or via linker molecules (e.g., immune system). 4.) Intercellular communication is also possible by channels between adjacent cells, which permit the exchange of ions and molecules and the spread of electric currents; many of those pores are arranged in the membranes of the contacting cells as a quasicristalline structure forming the gap junction. A national symposium on "Intercellular Communication" in Stuttgart on 16 and 17 September 1982 serving the aim of increased "interlaboratory communication" covered most of the above aspects.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 Membrane potential oscillations in homokaryons : an endogenous signal for detecting intercellular communication(1982) Hülser, Dieter F.; Lauterwasser, UrsulaFusion of cells by polyethylene glycol results in homokaryons with lower membrane input resistances than their parental cells, but otherwise unchanged membrane properties. With these large cells, long lasting intracellular recordings can be realized which are impossible with single parental cells. Homokaryons often display hyperpolarizing (up to 50 mV) oscillations of their membrane potentials. In electrically non-coupled cell lines (HeLa, L, Cl-1D) the frequencies of these endogenous signals are 3 oscillations per min. Trypsinized homokaryons of electrically coupled cell lines (BICR/M1R-K, 3T3, BT5C2) have frequencies of 0.3 oscillations per min. By recording the membrane potential oscillations of two contacting homokaryons, the formation of low resistance junctions was followed - without applying exogenous signals - by a superposition of the individual oscillations. Our electronmicroscopical investigations revealed that the intercellular coupling through the membranes of homokaryons can be attributed to gap junctions.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 Durchflusszytometrische Bestimmung der Farbstoffausbreitung über Gap-Junction-Kanäle(1999) Schulz, GunnarGap-Junction-Kanäle verbinden benachbarte Vertebraten-Zellen und ermöglichen den interzellulären Transfer von geladenen und ungeladenen Molekülen bis zu einem Molekulargewicht von 1 kd. Die Existenz funktioneller Gap-Junction-Kanäle kann mit Fluoreszenzfarbstoffen untersucht werden Dabei wird der Farbstoff durch eine Glasmikroelektrode in eine Zelle injiziert und die Kopplung durch Auszählen der gefärbten Zellen im Mikroskop bestimmt. Eine genauere Methode zur Quantifizierung der Zell-Zell Kopplung ist die Farbstoff-Beladungs-Technik mit Calcein AM. In dieser Arbeit wurde die Farbstoff-Beladungstechnik mit der Fluoreszenz aktivierten Durchflusszytometrie gekoppelt. Durch die große Anzahl der untersuchten Zellen eines Ansatzes ermöglicht diese Methode eine verbesserte Auflösung gegenüber der Injektions-methode. Es wurden die Kopplungsraten verschiedener Ansätze mit 6 Zell-Linien untersucht.Item Open Access Gap junctions: correlated electrophysiological recordings and ultrastructural analysis by fast freezing and freeze-fracturing(1989) Hülser, Dieter F.; Paschke, Dietmar; Greule, JoachimThe effect of glutardialdehyde on the dynamic organization of gap junctions cannot only be seen by electrophysiological measurements where the uncoupling of cells occurs within 3 min, but also by freeze fracturing the cells. Gap junctions from unfixed cells rapidly frozen by dipping into liquid propane appear polymorphic; loosely packed and clustered plaques are found, as well as tightly packed aggregates, which are mainly found in fixed preparations. Whether these different structures correspond with different functional states, or whether they depend on the local configuration of the contacting membranes is difficult to decide. The presented results, however, support the idea of active (coupling competent) gap junctions with loosely packed channels and nonactive (permanently closed) gap junctions where the channels are tightly packed.