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Item Open Access The use of the tip potential of glass microelectrodes in the determination of low cell membrane potentials(1973) Hülser, Dieter F.; Webb, Dennis J.The tip potential of Ling-Gerard glass microelectrodes changes upon insertion into cells and thus impedes the determination of the actual membrane potential. The lower the membrane potential of a cell, the larger will be the error due to this tip potential. However, as is demonstrated, a relationship exists between the tip potential of the electrode and the measured potential difference, which allows the determination of the membrane potential of a particular cell type by linear regression. This method showed that resting lymphocytes had no membrane potential, whereas for the slime mould Dictyostelitium discoideum a membrane potential of about -9 mV could be calculated.Item Open Access Der 24-Stunden-Aktivitätsrhythmus der Imago des Apfelwicklers (Carpocapsa pomonella L.)(1976) Skirkjavicjus, A.; Tat'janskajte, L.; Pertschi, Ottmar (Übersetzer)By the investigations carried out in 1969 it was established that day activity of imago form of Carpocapsa pomonella L. begins on an average at 1 p.m. and ends at 8 a.m. the next day. The rest of the time butterflies are sitting motionless. The peak of the activity is in the middle of the activity period and lasts 15 - 30 minutes. At this time the active butterflies make up 45.60 - 58.34 % of the whole number of those counted.Item Open Access 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.Item Open Access Characteristics of three nuclear emulsions for autoradiography at the electron microscope(1966) Hülser, Dieter F.; Rajewsky, Manfred F.Drei handelsübliche Kernspuremulsionen, Gevaert NUC 307, Ilford L4 und Kodak NTE, wurden wegen ihrer geringen Korngröße auf ihre Eignung zur elektronenmikroskopischen Autoradiographie untersucht. Korngrößenverteilungskurven wurden aufgenommen und ein geeigneter Entwickler ausgesucht. Zur Bestimmung der Empfindlichkeit dieser drei Emulsionen wurden Einkornschichten im Elektronenmikroskop mit Elektronen einer Energie von 5,7 keV, der mittleren beta-Energie des Tritiums, bestrahlt. Anschließend wurden die Emulsionen entwickelt, aber nicht fixiert. Mit dem Anteil der entwickelten AgBr-Körner kann dann über Trefferkurven die Empfindlichkeit der Emulsionen bestimmt werden. Man benötigt zur Bildung eines latenten Bildkeimes für die Ilford L4-Emulsion 1 - 1,4 Elektronen pro AgBr-Korn, für die Gevaert NUC 307-Emulsion 2 - 3 und für die Kodak NTE-Emulsion 4 - 5 Elektronen pro AgBr-Korn. Folgerungen für das Auflösevermögen bei radioaktiven Punkt- und Flächenquellen werden diskutiert. Fortschritte in der Mikroautoradiographie werden von der Entwicklung feinkörniger Emulsionen abhängen, deren Empfindlichkeit bei etwa einem Elektron pro AgBr-Korn liegen sollte.Item Open Access 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.Item Open Access 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.Item Open Access Untersuchungen zur Synchronisation in vivo: temporäre Inhibition der DNA-Synthese durch Hydroxyharnstoff in normalen und malignen Säugerzellsystemen(1971) Rajewsky, Manfred F.; Hülser, Dieter F.; Fabricius, ErikaDie Bearbeitung einer Reihe von Problemstellungen der experimentellen und klinischen Krebsforschung setzt die Möglichkeit einer Synchronisation proliferierender Zellsysteme in vivo voraus. Dies gilt z. B. für die Frage, ob bei Säugerzellen als Funktion ihrer Position im Zellcyclus Empfindlichkeitsunterschiede vorhanden sind, und zwar sowohl hinsichtlich der Auslösbarkeit des Prozesses der malignen Transformation durch Cancerogene, als auch in bezug auf die Inaktivierbarkeit maligner Zellen durch cytocide Agentien oder ionisierende Strahlung. In der vorliegenden Arbeit wird über Untersuchungen zur in vivo-Synchronisation verschiedener Gewebe (Embryo; Leber; Milz; transplantabler BICR/M1R-Tumor) der Ratte durch temporäre Blockade der DNA-Synthese mit Hydroxyharnstoff (HU) berichtet.Item Open Access Elektronenmikroskopische Befunde bei einer Affenseuche (Cercopithecus aethiops)(1968) May, Gerhard; Knothe, Hans; Hülser, Dieter F.; Herzberg, KurtDie elektronenmikroskopischen Befunde von G. Müller und D. Peters, die den Erreger einer Affenseuche (Cercopithecua aethiops) als gebogene Stäbe dargestellt haben, werden bestätigt und erweitert. Es gelang, die ätiologische Bedeutung dieser Formen durch die Kombination von Gewebekultur (menschliche Amnionzellen), Tierversuch (Meerschweinchen) und elektronenmikroskopischem Befund in dieser Reihenfolge zu sichern.Item Open Access Elektronenmikroskopische Autoradiogramme: unterschiedliche Empfindlichkeit von Photoemulsionen gegenüber Tritium(1971) Hülser, Dieter F.; Rajewsky, Manfred F.The sensitivity of the photographic emulsion is an important factor in the resolution of autoradiographs at the electron microscopic level. In a number of recent publications, single hit processes have been considered sufficient for the production of developable latent images by tritium electrons. However, since the absorbed energy required or latent image formation in AgBr crystals of commercially available emulsions is of the order of 800 eV, onIy low energy tritium electrons (up to 3 keV) will produce latent images by single hit processes in small AgBr crystals of about 400 A diameter. In emulsions with larger AgBr crystals (about 1000 A diameter), electrons with an energy of up to about 6 keV can be regisiered by single hit processes. Evidently, latent image formation may also result from multiple hits by electrons of higher energy. Since the energy absorption required for latent image formation is constant, the sensitivity of photographic emulsions must be considered proportional to the diameter of the respective AgBr crystals, unless methods become available for specific sensitization of emulsions with small AgBr crystals.Item Open Access Ionic coupling between nonexcitable cells in culture(1974) Hülser, Dieter F.In the following sections, the electrophysiological techniques used for the demonstration of low-resistance junctions by the occurrence of ionic coupling pulses will be described. It will also be shown that for the analysis of coupling phenomena between cells, electrical parameters such as potential difference, membrane resistance, and capacitance must be taken into account. In addition, the electrical and mechanical instrumentation necessary for such measurements will be described with special emphasis on electrophysiological studies in cultured cells. Based on experiments with lymphocytes it will be shown that low-resistance junctions can be built up within minutes and that in the case of cells of established lines in culture their existence is related neither to normal nor to malignant cell properties, but appears to be associated with fibroblastoid cells.