Die Wirkung von Adenin und Urazil auf das Wachstum vonB. coli commune

Summary The growth ofBacterium coli commune in culture-medium afterFriedlein containing glucose was controled by photometry. Addition of uracil hastens the growth slightly, addition of adenin delays it. The curve of growth with adenin shows two maxima similarly as the primary and secundary effect after irradiation of biological material by ultrashort rays. As known the irradiation of nucleic-acids sets in partial freedom purins and pyrimidins. These are changed again by intense irradiation. The news products of irradiation have probably also biological influences.     

Natural selection for resistance to mercury pollution

Summary The survival under conditions of mercury pollution of two natural populations of the marine gastropodCerithium rupestre, derived from mercury-polluted and mercury-free sites, was tested in the laboratory. The results indicate a significantly higher survival rate for animals derived from the mercury-polluted site, in each of six repetitive experiments. We conclude that mercury resistance in marine organisms is reinforced in mercury polluted sites, presumably by natural selection for increased resistance. The evolution of metal tolerance in marine organisms may be as fast as that of metal tolerance in plants and the evolution of industrial melanisms in moths.     

A micro-electrode amplifier with an infinite resistance current source for intracellular measurements of membrane potential and resistance changes under current clamp

Summary A microelectrode amplifier for intracellular electrophysiological research is described. It is equipped with an electronic infinite resistance constant current source for the injection of current into biological cells. With this amplifier the potential changes, the resistance changes and the dependence on extrinsic current of single cells can be measured independently and simultaneously.Acknowledgments. I am grateful to Dr D.G. Stavenga who inspired me to start the design. I thank P. Cuperus for stimulating discussions and A.J.Th. Liebrand for the construction of the amplifier. This work was supported financially by the Netherlands Organisation for the Advancement of Pure Research (Z.W.O.).     

Asymmetrical responses to directional selection for radiation resistance and sensitivity inDrosophila

Zusammenfassung Es wurde eine Selektion auf Strahlenresistenz nach Bestrahlung vonDrosophila melanogaster mit⁶⁰Co--Strahlen während 5 Generationen mit gutem Erfolg erzielt, nicht aber eine solche auf erhöhte Strahlensensibilität. Der asymmetrische Selektionseffekt dürfte somit auf dominanter Vererbung der Resistenz beruhen. Familienselektion kann auch ohne Besthralung zu resistenten Stämmen führen.     

A micro-electrode amplifier with an infinite resistance current source for intracellular measurements of membrane potential and resistance changes under current clamp.

A microelectrode amplifier for intracellular electrophysiological research is described. It is equipped with an electronic infinite resistance constant current source for the injection of current into biological cells. With this amplifier the potential changes, the resistance changes and the dependence on extrinsic current of single cells can be measured independently and simultaneously.     

Die katalytische Mutation der Ionen Al3+ und MoO

Summary The catalytic mutation of the ions Al³⁺ and MoO ₄ ^2– on the mixed carrier Cd(OH)₂/Co(OH)₂(Tr) is recognizable by the fact that the combination Tr+Al³⁺+MoO ₄ ^2– is more active in the decomposition of H₂O₂ than the combination Tr+MoO ₄ ^2– +Al³⁺.     

Novel substrates for the kinetic assay of esterases associated with insecticide resistance

Naphthalene thioesters were synthesized as substrates for a continuous, non- disruptive kinetic assay of general carboxylesterase activity. The continuous nature of the assay is based on the production of a soluble dianion chromophore from the reaction of naphthalene thio with 5,5-dithiobis (2-nitrobenzoic acid). Applications with 1- and 2-naphthalene thioacetates demonstrated their use in a fast accurate kinetic microassay of esterase activity, using porcine carboxylesterase as a model. These novel esters proved to be useful as substrates for the spectrophotometric assay of insecticide-resistance in two aphid species and may be applicable to other esterasebased diagnostic procedures.     

Intercellular pathways in the heart: Direct evidence for low resistance channels

Zusammenfassung In einzelne Zellen von Kaninchen-und Rattenherzen wurde Natriumfluoreszin injiziert, wobei der Farbstoff direkt von Zelle zu Zelle diffundierte, aber nicht merklich auf den Extrazellulärraum übertritt. Daraus wird gefolgert, dass zwischen den Myocardzellen Verbindungswege existieren, von wo aus Impulse weitergeleitet werden können.

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Supported by grants Nos. HL 13517, GM 15991 and GM 16436 from the National Institutes of Health.     

Griseofulvin resistance in dermatophytes

Zusammenfassung Häufigkeit und Eigenschaften der griseofulvinresistenten Mutanten vonMicrosporum gypseum wurden geprüft. 2 Loci, durch welche die Resistenz gesteuert wird, wurden in verschiedenen Kopplungsgruppen identifiziert und im Vergleich mit dem Ausgangsstamm die Resistenz bei allen Mutanten hundertfach vergrössert.     

Antibiotic resistance in microbes

The treatment of infectious disease is compromised by the development of antibiotic-resistant strains of microbial pathogens. A variety of biochemical processes are involved that may keep antibiotics out of the cell, alter the target of the drug, or disable the antibiotic. Studies have shown that resistance determinants arise by either of two genetic mechanisms: mutation and acquisition. Antibiotic resistance genes can be disseminated among bacterial populations by several processes, but principally by conjugation. Thus the overall problem of antibiotic resistance is one of genetic ecology and a better understanding of the contributing parameters is necessary to devise rational approaches to reduce the development and spread of antibiotic resistance and so avoid a critical situation in therapy--a return to a pre-antibiotic era.     

Selection for resistance to azadirachtin in the green peach aphid,Myzus persicae

Two lines ofMyzus persicae of the same origin were treated repeatedlywith pure azadirachtin (aza), or a refined neem seed extract (NSE), at the equivalent concentration of aza. After 40 generations, the aza-selected line had developed 9-fold resistance to aza compared to a non-selected control line, whereas the NSE-selected line did not. These results suggest that a blend of active constitutents in a botanical insecticide such as neem might diffuse the selection process, mitigating the development of resistance compared to that expected with a single active ingredient.     

Disease resistance in farm animals

Genetic variations in disease resistance of farm animals can be observed at all levels of defence against infectious agents. In most cases susceptibility to infections has polygenic origins. In domestic animals only a few instances of a single genetic locus responsible for disease resistance are known. A well-examined example is the Mx1 gene product of certain mice strains conferring selective resistance to influenza virus infections. Attempts to improve disease resistance by gene transfer of different gene constructs into farm animals include the use of monoclonal antibody gene constructs, transgenes consisting of antisense RNA genes directed against viruses and Mx1 cDNA containing transgenes.     

Cardiac pressoreceptors and peripheral resistance

Summary The results obtained show that the pressoreceptors, probably ubicated in the left ventricle of the rat, respond to the distention with vasodilatation. The afferent tract of this reflex is in the vagus nerve and the efferent one is in the sympathetic nervous system. The probable function of this reflex is discussed.