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Biomedical subjects

W Jahn

Publications and source records attributed to W Jahn.

At least 19 recordsLinked to original sources
PubMed1991

Argiotoxin636 inhibits NMDA-activated ion channels expressed in Xenopus oocytes.

Argiotoxin636, a component of the spider venom of argiope species, was chemically synthesized together with a number of derivatives in order to analyse their blocking activity on mammalian glutamate receptors. Xenopus laevis oocytes injected with rat brain mRNA served as assay system. The results showed that argiotoxin636 had a higher affinity for N-methyl-D-aspartate (NMDA) than for kainate receptors, blocking the corresponding ion channels in a voltage-dependent manner. Modifications of the polyamine tail or the terminal arginine residue strongly reduced the blocking potency. The iodinated monohydroxyl phenylderivatives, however, retained their NMDA-selective binding and could serve as non-competitive antagonists for radioligand binding assays aiding in the biochemical isolation of glutamate receptors.

Animals↗
PubMed1989

Novel procedures for derivatization of ribosomes for crystallographic studies.

Undecagold and tetrairidium clusters have been used for the preparation of heavy-metal derivatives of ribosomal particles, necessary for the evaluation of phases in the x-ray structure determination of these large particles. To obtain specific binding, monofunctional reagents of the clusters were prepared and were covalently bound to free sulfhydryl groups on the surface of the ribosome. In addition, a mutant of Bacillus stearothermophilus which lacks one ribosomal protein (BL11) was grown. The heavy-atom clusters were covalently bound to isolated protein BL11, and the modified protein was consequently reconstituted into the mutated ribosomal subunits. Crystallographic data have been collected from crystals of native particles, from the mutated ones, and from the iridium- and gold-derivatized subunits. All these crystal forms are isomorphous within the experimental error.

Crystallization↗
PubMed1989

[Age changes of functional nuclear swelling and classes of nuclei in human hepatocytes].

The aim of the study was to describe aging changes in the functional nuclear edema and the classification of human hepatocyte nuclei, by determining three parameters--the size of the nucleus, the relative DNA quantity and the number of chromocenters. For this purpose, karyometry and DNA cytophotometry were performed on 10 human liver preparations. The data obtained was subjected to correlation, cluster and discriminance analysis. The results indicated a reduction in the capacity of liver cells for functional nuclear edema as aging progressed. Whereas at a young age there is only a loose correlation between nuclear size and DNA content, it becomes much stricter later on, partly caused by polyploidization. Cluster analysis, followed by discriminance analysis, is well suited for dividing the nuclei of human hepatocytes into two or three statistical populations provided the nuclear area, DNA quantity and number of chromocenters are all used as characteristics simultaneously. When allowance is made for functional edema, the biological interpretation of clusters from young liver preparations permits meaningful conclusions, but it appears problematic for old preparations. Here it might be more practical to analyze the mixed distributions resulting from a determination of the DNA quantity or nuclear size alone.

Aging↗
PubMed1989

[Random sample planning in morphometry].

This report tries to explain principles and presuppositions of planning sample sizes. The aim is estimation of the optimal, that means minimally necessary sample size, justifying an investigation ethically and economically. The problems are complicated because of the necessity of nested sampling or samples within samples. We describe the most important presuppositions using an example of mean value estimation. These are: establishing of demands for exactness, of error probability, and knowledge of variance of the parameters. It is explained in detail by means of binomially distributed variables as we find them in the point counting method.

Humans↗
PubMed1987

Antamanide antagonizes the phalloidin-induced negative inotropic effect and blocks voltage dependently the fast outward K+ current in voltage-clamped frog muscle fibres.

The effects of antamanide (10(-14)-10(-5) M) and N-acetyl-secophalloidin (10(-7)-5 X 10(-3) M) a neutral non-toxic derivative of phalloidin, were tested on voltage-clamped single frog muscle fibres. Antamanide protected muscle fibres against the negative inotropic effect of phalloidin but blocked the fast potassium permeability in the same concentration range and the same voltage-dependent manner as did phalloidin. N-Acetyl-secophalloidin exhibited a strongly attenuated blocking effect on K+ permeability in a 1,000-fold higher concentration range than phalloidin. Neither antamanide nor N-acetyl-secophalloidin affected the contractile properties. These results suggest the existence in the frog muscle membrane of a receptor with two sites for phalloidin and antamanide which acts on potassium conductance.

Animals↗
PubMed1986

[Biostatistical models in experimental gerontology].

Morphometric measuring values present themselves in a definite distribution which changes in the ageing process. This change of distribution can be clarified by distribution analyses. Another task within the analysis of frequency distributions is the decomposition of mixed distributions, as they may appear in various parameters in the course of life. The linear regression analysis is, for instance, to be used in the verification of sexual divergencies in the process of ageing. An adaptation of non-linear exponential functions to series of measuring values serves, among others, to make evidence concerning the ageing rapidity of the tissues. When in gerontological inquiries at the same time many different characteristics are determined also the degree of their ageing dependency is of interest. This is to be established by means of a special transformation within the factor analysis. Finally the study shows instances for the application of contingency tables in qualitative characteristics and the investigation of their frequency in the process of ageing as well as for the use of the cluster analysis.

Adolescent↗
PubMed1986

[Discussion of errors and measuring strategies in morphometry using analysis of variance].

Statistical techniques known as the analysis of variance make it possible for the morphologist to plan work in such a way as to get quantitative data with the greatest possible economy of effort. This paper explains how to decide how many measurements to make per micrograph, how many micrographs per tissue block or organ, and how many organs or individuals are necessary for getting an exactness of sufficient quality of the results. The examples furnished have been taken from measuring volume densities of mitochondria in heart muscle cells and from cell counting in lymph nodes. Finally we show, how to determine sample sizes, if we are interested in demonstration of significant differences between mean values.

Analysis of Variance↗
PubMed1985

Alpha-1-antitrypsin: evidence for a fifth PI M subtype and a new deficiency allele PI*Z augsburg.

The phenotypes of the protease inhibitor (PI) alpha-1-antitrypsin have been analyzed by isoelectric focusing on polyacrylamide gels. With improved resolution by a modified procedure it was possible to demonstrate a fifth PI*M suballele. The bands of PI M5 are located between PI M1 and PI M3. In addition, a further deficiency allele similar to PI*Z was found in a female patient with obstructive pulmonary disease. This variant was provisionally named PI Z augsburg (PI Z aug). Family data confirm a simple codominant mode of inheritance for PI Z aug.

Adult↗
PubMed1979

Cytochalasin D is able to mimic the effects of phalloidin on the rat liver.

Cytochalasin D induces a strong potassium release in the isolated perfused rat liver and leads to vacuolization of the liver parenchymal cells. These effects are similar to the action of phalloidin on the rat liver. Since phalloidin and cytochalasin act in a different way on microfilaments, it is suggested that any disturbance of the function of microfilaments can induce these effects.

Animals↗