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Biomedical subjects

W Pfeiffer

Publications and source records attributed to W Pfeiffer.

At least 19 recordsLinked to original sources
PubMed2006

Parameters for cellular viability and membrane function in chenopodium cells show a specific response of extracellular pH to heat shock with extreme Q10.

The effect of brief heat shock on Chenopodium cells was investigated by measuring biochemical parameters for cellular vitality, membrane function and integrity: extracellular pH, release of osmotic compounds, phosphatase, protein and betalain, and cellular reduction of DCPIP and MTT. A threshold temperature was found at 45 degrees C, where release of osmotic compounds, protein and betalain, and reduction of DCPIP and MTT indicate loss of vitality. Extracellular pH and an alkaline phosphatase responded 10-20 degrees C below this threshold, suggesting that extracellular alkalinization, and probably the release of a phosphatase, are part of a specific cellular response to abiotic stress induced by heat shock. The extracellular proton concentration did not increase above 45 degrees C: this may indicate equilibration of gradients driving this process or an inactivation of cellular mechanisms responsible for extracellular alkalinization. The response of extracellular pH to heat shock in Chenopodium cell suspensions was fast, i.e., up to +1 pH in 5 min. Addition of the K+/H+ antiporter nigericin to Chenopodium cells caused an extracellular alkalinization similar to heat shock. The heat shock-induced extracellular alkalinization was characterized by Q10 values for distinct ranges of temperature (Q10 of 56 for 24-31 degrees C, 2.3 for 31-42 degrees C, and 1.0 for 42-50 degrees C). To the author's knowledge, the Q10 of 56 is the highest found up to now. These results suggest that extracellular protons are involved in temperature sensing and signalling in plant cells, probably via a channel-mediated pathway.

2,6-Dichloroindophenol↗
PubMed2005

Nanoscopic ultrafast space-time-resolved spectroscopy.

We propose and analyze a scheme for ultrafast spectroscopy with nanometer spatial and femtosecond temporal resolution. The interaction of polarization-shaped laser pulses with a nanostructure allows us to control the spatial and temporal evolution of the optical near field. Employing a learning algorithm, the field is tailored such that pump and probe excitation occur at different positions and at different times. Both excitations can be restricted to subdiffraction extensions and are separable on a nanometer length scale. This enables the direct spatial probing of nanoscale energy transfer or charge transfer processes.

Journal Article↗
PubMed2000

Surface plasmon dynamics in silver nanoparticles studied by femtosecond time-resolved photoemission.

Multiphoton photoelectron spectroscopy reveals the multiple excitation of the surface plasmon in silver nanoparticles on graphite. Resonant excitation of the surface plasmon with 400 nm femtosecond radiation allows one to distinguish between photoemission from the nanoparticles and the substrate. Two different previously unobserved decay channels of the collective excitation have been identified, namely, decay into one or several single-particle excitations.

Journal Article↗
PubMed1997

Frequency distributions of fish parasites in the perch Perca fluviatilis L. from Lake Constance.

Seventy perch (Perca fluviatilis) caught in Lake Constance at Langenargen in May 1990 were examined for parasites. The frequency distributions of the eyefluke Diplostomum spathaceum (Rudolphi, 1819), and the tapeworms Proteocephalus percae (Müller, 1780) and Triaenophorus nodulosus (Pallas, 1781) fitted closely to a negative binomial. Only a few fish were highly parasitized. These fishes are devoured by the final hosts: gulls (Diplostomum spathaceum) or the pike (Triaenophorus nodulosus). The fish population was influenced negligibly and the parasite population stayed at a moderate level. During the spawning period female perch were infested with Proteocephalus percae more than the males. This may be because the females had a higher food consumption and became more infected by copepods (intermediate hosts). In contrast, Diplostomum spathaceum, Ichthyocotylurus variegatus, Triaenophorus nodulosus, and Tylodelphys clavata did not occur in different numbers in female and male perches. The frequency distribution of Ichthyocotylurus variegatus (Creplin, 1825) and Tylodelphys clavata (Nordmann, 1832) did not conform to a negative binomial.

Animals↗
PubMed1997

Seasonal differences in infestation of the perch Perca fluviatilis L. from Lake Constance with digenean trematodes.

Perch (Perca fluviatilis L.) caught in Lake Constance every 2 months over a period of 3 years below six towns or villages (Langenargen, Nonnenhorn, Rorschach, Romanshorn, Bottighofen, and the Lake of Uberlingen) were examined for parasites. In contrast to Diplostomum spathaceum (Rudolphi, 1819) and Tylodelphys clavata (Nordmann, 1832), Bunodera luciopercae (Müller, 1776) and Ichthyocotylurus variegatus (Creplin, 1825) showed marked seasonal differences. These differences were influenced by various factors: the different numbers of the first intermediate hosts (snails, copepods), the water temperature, the physiological state of the fish, and its way of life.

Animals↗
PubMed1997

The parasitism of fish from Lake Constance--a comparison of present and earlier data.

Commercial fish (perch, roach, bream, dace, and burbot) were caught below Langenargen in 1988-1990. Their infestation with cestodes and digenean trematodes was studied. The results were compared with earlier data. The infestation of perch with Diplostomum spathaceum and Ichthyocotylurus variegatus noted in 1988-1990 had increased as compared with that observed in 1974-1976. The infestation of perch with Triaenophorus nodulosus seen in 1990 had increased as opposed to that noted in 1988. The infestation of bream with D. spathaceum and of perch and roach with Tylodelphys clavata observed in 1988-1990 had remained the same as that seen in 1974-1976. The infestation of perch with D. spathaceum noted in 1988-1990 had decreased as opposed to that reported for 1974-1976. The infestation of bream, dace, and burbot with T. clavata noted in 1988-1990 had decreased as compared with that observed in 1974-1976. The infestation of perch with T. nodulosus seen in 1988/1989 had decreased as opposed to that noted in 1974-1976. All three cyprinids studied as well as the burbot had been less intensively infested in 1988-1990 than in 1974-1976. Only perch had been more intensively infested in 1988-1990 than in 1974-1976, especially with D. spathaceum and I. variegatus.

Animals↗
PubMed1991

Lateral order in binary lipid alloys and its coupling to membrane functions.

Densitometry, Raman spectroscopy and small angle neutron scattering are employed to elucidate the miscibility behavior of lipid mixtures organized as liposomal dispersions. First, temperature-composition-phase diagrams for several binary alloys of dialkyl-lecithins differing in chain lengths by an increasing number of CH2-groups are derived. A mixture of dimyristoyllecithin and distearoyllecithin (delta CH2 = 4) shows a peritectic phase behavior with a miscibility gap in the gel state. In the fluid phase, at high enough temperatures, homogeneous mixtures of the two components are formed at all molar ratios. However, upon approaching a critical point by either lowering the temperature or increasing the hydrostatic pressure, critical concentration fluctuations are observed. If one component of a binary mixture is charged, electrostatic interactions can be used to induce phase separation at constant temperature. This is demonstrated for Ca2(+)-driven demixing in alloys of lecithin and negatively charged phosphatidylglycerol. The influence of the various concepts for the induction of lateral structure formation in lipid membranes on integral functional units like ionophores is demonstrated by analysing the single channel current fluctuations of gramicidin in bimolecular lipid membranes. Ca2+, as well as polyelectrolyte-induced phase separations are shown and discussed as examples for the important (lateral) order-function relationship in biomembranes.

Electrochemistry↗
PubMed1991

The motivation of alcohol dependents to undergo treatment.

The purpose of this study was to investigate the determinants and factors influencing the motivation of alcohol dependents to undergo treatment. As well as exploring the influence of socio-demographic and illness-related variables, the study concentrated in particular on the influence of the clients' attitudes towards their current life situation, their alcohol problem and the treatment, also the influence of specific interventions aimed at increasing their motivation for treatment. On the basis of the results obtained in the study from 239 alcohol-dependent clients, it is shown to what extent these variables are of value as a means of predicting and modifying the motivation for treatment. In the motivation programme a variety of procedures was applied using a 2 x 2 design: motivation on an individual basis and motivation on a group basis were combined with two different approaches, one client-centred and one in accordance with the principles of cognitive-behavioural therapy. A group placed on a waiting list for 3 weeks was used as a control group. The clients were allocated to the various groups on a random basis. Specific attitudes on the part of the clients and aspects of the motivation programme provided significant indicators of the clients' likelihood to undergo treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

[Adverse effects of long-term psychopharmacologic therapy on sexual functions].

103 patients who were in a psychopathologically relatively stable condition and under long-term psycho-pharmacological treatment on an outpatient basis, were questioned on sexual functional disorders and changes in sexual behaviour, basing on a semistructured interview. This is of particular importance with regard to compliance problems in long-term therapy. 50% of the patients stated that there had been changes from the beginning of the psychiatric disorders, mostly as functional sexual disorders (42%). Multifactorial causes were presumed in most of the cases; the medication was thought to be solely responsible in only 15% of all the cases (expert rating). Schizophrenic patients under neuroleptic treatment were most frequently affected by functional disturbances. In some of the patients of the total random sample (36 patients) medication was changed under experimental conditions for a period of four weeks. Improvement of the sexual function was most frequently stated whenever a medication was given with a reduced dosage; however, the examined partial random sample is very small.

Adult↗
PubMed1990

Copper in silicon.

Explore the source record for details and available documents.

Journal Article↗
PubMed1989

Lateral order in mixed lipid bilayers and its influence on ion translocation by gramicidin: a model for the structure-function relationship in membranes.

The temperature-composition phase diagram of dimyristoylphosphatidylcholine and dipentadecylphosphatidylglycerol (DiC15PG) was determined by mass densitometry. For a mixture containing 30 mol% DiC15PG, the homogeneous distribution of the 2 components is demonstrated in the fluid state at T = 35 degrees C by small-angle neutron scattering in combination with the inverse contrast variation method. By the same technique, the coexistence of fluid and condensed phases at T = 23.3 degrees C could be shown in agreement with the densitometric data. Furthermore, it is demonstrated that Ca++ induces, even at T = 35 degrees C, separation into 2 fluid phases. A corresponding phase separation is found in bimolecular lipid membranes ("black films") by analysis of the single-channel conductance fluctuations of gramicidin A incorporated into an equimolarly mixed membrane of neutral lecithin and charged phosphatidic acid. The results are discussed as primary examples on the model-membrane level for the important structure-function relationship of biomembranes.

Calcium↗
PubMed1989

[History of the development of some ophthalmologic instruments by Carl Zeiss].

Starting with the corneal microscope of 1898, numerous ophthalmological instruments have been developed at Zeiss in cooperation with important eye doctors. Examples are retinal cameras, slitlamps, the photo slitlamp, the keratometer, surgical microscopes and the photocoagulator. As an optical feature, some of these instruments exhibit parallel beam paths making easier the construction of modular systems.

Germany↗
PubMed1988

Structural properties of a phosphatidylcholine-cholesterol system as studied by small-angle neutron scattering: ripple structure and phase diagram.

Small-angle neutron scattering has been used to study structural features of lamellar bilayer membranes of dimyristoylphosphatidylcholine (DMPC) and DMPC mixed with various amount of cholesterol. The studies were recorded at a fixed hydration level of 17% 2H2O, i.e. just below saturation. Bragg reflections gives information on the ripple structure and on the bilayer periodicity. The crystalline Lc phase, which was stabilized after long time storage at low temperature, exhibits major small angle scattering when cholesterol is mixed into the membrane. The intermediate P beta' gel-phase, which is characteristic by the rippled structure, is dramatically stabilized by the introduction of cholesterol. The ripple structure depends significantly both on the cholesterol content and on the temperature. At high temperatures, T greater than 15 degrees C, the inverse ripple periodicity varies basically linearly with cholesterol content, and approach zero (i.e. periodicity goes to infinite) at 20 mol% cholesterol, approximately. At lower temperatures the correlation is more complex. The data indicate additional phase boundaries below 2 mol% and at approx. 8 mol%. Secondary rippled structures are observed in the low temperature L beta'-phase for cholesterol content below approx. 8 mol%. The data gives detailed insight into the phosphatidylcholine cholesterol phase diagram, which is discussed on the basis of a simple model in which the cholesterol complexes are fixed to the defect stripes of the rippled structure.

Cholesterol↗
PubMed1980

Accessibility of expressed and non-expressed genes to a restriction nuclease.

Nuclei of mouse liver and an immunoglobulin producing myeloma were digested with HaeIII or its isoschizomer BspRI. The DNA fragment patterns after electrophoresis, blotting, and hybridization were very similar for the two types of nuclei when a probe for the non-expressed beta-globin gene was used. The constant (C) region of the kappa light chain gene, on the other hand, was more accessible to the nuclease in myeloma than on liver nuclei. In myeloma nuclei the BspRI sites were about equally sensitive, in fact the pattern resembled a partial digestion pattern of free DNA. In contrast, in liver nuclei some sites were much more protected than others. This is interpreted by assuming that this single copy non-expressed gene region is covered by nucleosomes which are preferentially located on certain DNA sequences. Restriction nuclease digestion of nuclei seems to be a promising method for the analysis of genes in their expressed and non-expressed states.

Animals↗