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Biomedical subjects

U Zimmermann

Publications and source records attributed to U Zimmermann.

At least 19 recordsLinked to original sources
PubMed1992

Stably inherited killer activity in industrial yeast strains obtained by electrotransformation.

Killer-sensitive strains of Saccharomyces cerevisiae and Saccharomyces carlsbergensis were transformed by electroinjection using double-stranded RNA isolated from a superkiller strain. Various recipient strains were used: both thermo-resistant and thermo-sensitive as well as mutants of industrial strains. Conversion of respiratory competent (rho+) into respiratory deficient (rho-) strains (mutants) resulted in a significant increase of the yield of electrotransformants and/or of longterm killer stability. Electrotransformation of rho- mutants of distillery and brewery strains resulted in more than 100 clones, which exhibited weak or strong killer activity over some or all of the experimental period of 10 months.

DNA, Mitochondrial↗
PubMed1992

Levitation, holding, and rotation of cells within traps made by high-frequency fields.

Biological cells and other particles can be electrically manipulated by means of negative dielectrophoresis within microchambers whose electrode geometry is of the order of the cell size. Very-high-frequency fields (50 MHz and above) and media of increased relative permittivity are especially suitable for the purpose, as shown by experimental data on levitation and rotation. It appears to be possible to move and rotate cells or particles at will using this technology.

Cytological Techniques↗
PubMed1992

Production of mitogen-contamination free alginates with variable ratios of mannuronic acid to guluronic acid by free flow electrophoresis.

Commercial alginates consisting of variable homopolymeric regions of beta-D-mannuronic acid and alpha-L-guluronic acid, interspaced with regions of alternating blocks, are potent stimulators of macrophages and lymphocytes. Therefore, inflammatory reactions and fibrotic overgrowth of the beads result if Langerhans islets are encapsulated in raw alginate hydrogel beads (cross-linked with divalent cations). The result is random failure of the islets some time after transplantation. Analysis of raw alginates by using free flow electrophoresis demonstrated that commercial alginates contained at least 10-20 fractions (characterized by different electrophoretic mobilities) which showed mitogenic activity. These fractions could be quantitatively separated from the alginic acids by free flow electrophoresis on a preparative scale. The purified alginates cross-linked with Ca2+ ions exhibited no mitogenic reactions as proved by an in vitro assay. In addition, examination of purified Ba2+ alginate beads implanted intraperitoneally in rats or mice for three weeks showed no fibrotic overgrowth in contrast to implants made from unpurified alginate.

Alginates↗
PubMed1992

Alginate coating of islets of Langerhans: in vitro studies on a new method for microencapsulation for immuno-isolated transplantation.

Immuno-isolated transplantation offers the attractive prospect of being able to transplant xenogeneic islets without immunosuppression. This study introduces a completely new method of coating single islets using a homogeneous alginate membrane approximately 10 microns thick. During glucose challenge (perifusion and static incubation) encapsulated islets show the same pattern and quantity of insulin release as non-encapsulated controls. This encapsulation method markedly reduces the amount of transplanted material by reducing the size of the capsule. It is suggested that encapsulated islets may be transplanted into sites such as the renal capsule or omentum or even by intraportal injection into the liver.

Alginates↗
PubMed1992

Human hybridoma generation by hypo-osmolar electrofusion: characterization of human monoclonal antibodies to Schistosoma mansoni parasite antigens.

Human monoclonal antibodies which bind Schistosoma mansoni worm and egg antigens were identified and characterized from hybridomas generated using the hypo-osmolar electrofusion technique of somatic cell fusion. Splenocytes from S. mansoni infected individuals were mitogen-activated in vitro and subsequently fused by electrofusion. The greatest number of HAT resistant hybridomas per helical fusion chamber was obtained with unfrozen splenocytes cultured for 4-6 days after introduction of mitogen. Hybridomas secreting IgG antibodies recognizing parasite antigens were identified by ELISA. Twenty-one cloned cell lines secreting IgG antibody were maintained for at least 6 months. Characterization of antigen reactivity by Western blot analysis of nien cloned cell lines revealed antibodies which bound stage specific parasitic antigens. The data show that the technique of hypo-osmolar electrofusion produces stable, antibody producing hybridomas. The human monoclonal antibodies screened represent candidate molecules useful in the investigations of the human pathogen S. mansoni.

Animals↗
PubMed1992

Electrically evoked motile responses of mammalian type I vestibular hair cells.

Vestibular hair cells, type I and II, with membrane potentials around -64 mV were prepared from guinea pig ampullar cristae and maculae. In type I cells, current injection, application of voltage steps during membrane patch-clamping, or extracellular alternating current (ac) fields evoked fast length changes of 50 nm to 500 nm of the cell "neck." Mechanical responses were determined by computerized video techniques with contrast-enhanced digital image subtraction (DIS) and interpeak pixel counts (IPPC) or by double photodiode measurements. These techniques allowed spatial resolutions of 300 nm, 120 nm, and 50 nm, respectively. In contrast to measurements of high-frequency movements of auditory outer hair cells (OHCs), the mechanical responses of type I VHCs were restricted to low frequencies below 85 Hz. In addition to recently reported slow motility of VHCs, the present results suggest that fast mechanical VHC responses could significantly influence macular and cupular mechanics. Isometric and isotonic variants are discussed. The observed frequency maxima gap between VHCs and OHCs is suggested to contribute to a clear separation of the auditory and the vestibular sensory modality.

Animals↗
PubMed1992

Microscale production of hybridomas by hypo-osmolar electrofusion.

We have developed and tested a novel electrofusion chamber, the adjustable plate microchamber, that permits the successful electrofusion and production of hybridomas in a hanging droplet from as few as 1,000 B lymphocytes. Cell suspension volumes of 10 microliters may be used without excessive difficulty in aseptically recovering fused cells. With a modification of the hypo-osmolar electrofusion protocol with this microchamber, fusion efficiencies of the order of 10(-3) may be attained. These efficiencies are comparable to those attained with standard hardware and much higher numbers of input B lymphocytes. This technology should permit high efficiency hybridoma production using a variety of hitherto inaccessible B lymphocyte populations such as B cells isolated from human organ biopsies.

Animals↗
PubMed1991

Selection of hybrid plants obtained by electrofusion of vacuolated x evacuolated plant protoplasts in hypo-osmolar solution.

Vacuolated and evacuolated tobacco mesophyll protoplasts were electrically fused in hypo-osmolar media by using an alternating field of modulated amplitude for alignment. The vacuolated fusion partner was isolated from Nicotiana tabaccum L. cv Xanthi and the evacuolated one from the streptomycin-resistant strain Nicotiana tabaccum L. cv Petit Havana SR1. The field and osmolarity conditions used ensured relatively high yields of heterologous fusion products despite the differences in density and size of the parental cells. After removal of the evacuolated, streptomycin-resistant fused and unfused protoplasts by flotation of vacuole-containing cells on iso-osmolar sucrose medium, the cybrids and hybrids were cultured in 25 microliters drops of agarose. During the first 5 weeks the non-fused Xanthi-protoplasts were used as a nurse culture. After addition of streptomycin to the growth media, cybrids and hybrids were successfully selected whereas fused and unfused vacuole-containing protoplasts died within 6 days. Only the streptomycin-resistant cybrids and hybrids developed into whole plants. On average a yield of 0.025% of streptomycin-resistant plants (referred to the total number of parental cells) was obtained. Polyacrylamide gel electrophoresis of leaf extracts of these plants showed that at least 50% of the streptomycin-resistant plants had a hybrid-esterase isoenzyme pattern. The protocol can be generalised by fusion of iodoacetamide-inactivated vacuolated protoplasts with meristematic (or evacuolized) protoplasts carrying no genetic marker. Use of evacolated protoplasts for electrofusion with vacuole-containing protoplasts therefore offers a way of overcoming the lack of suitable genetic markers for hybrid selection.

Electric Stimulation↗
PubMed1991

Divalent cation-sensitive pores formed by natural and synthetic melittin and by Triton X-100.

Leakage of ions and low-molecular-weight metabolites from Lettre cells is induced by synthetic melittin, as effectively as by melittin isolated from bee venom; in each case leakage is inhibited by Ca2+, Zn2+ or H+. Inhibition of leakage by divalent cations is reversible in that Lettre cells incubated with melittin (or with Triton X-100) in the presence of inhibitory amounts of Zn2+, when freed of Zn2+ by EGTA or by centrifugation, begin to leak (in Zn2(+)-sensitive manner). Electrorotation of Lettre cells is altered by melittin, compatible with membrane permeabilization; melittin plus Zn2+ does not alter electrorotation until Zn2+ (and unbound melittin) are removed. Melittin or Triton X-100 added to calcein-loaded liposomes induces leakage of calcein; divalent cations inhibit. Energy transfer between liposome-associated melittin and 2-, 7- or 12-(9-anthroyloxy)stearate (AS) is maximal with 12-AS; addition of Zn2+ has little effect. Circular dichroism spectra of melittin plus liposomes are unaffected by Zn2+. These results show that the formation of divalent cation-sensitive pores is not dependent on the presence of endogenous membrane proteins and that the action of divalent cations is not by displacement of melittin (or Triton) from the lipid bilayer.

Animals↗
PubMed1991

Influence of intratracheal application of fluorocarbon 72 and different lipid-mixtures on mechanical behavior of isolated immature pig lungs.

Substitution of surfactant in immature lungs has two functional targets: the reduction of the overall alveolar surface tension and the mechanical stabilization of the system of alveoli having different diameters. Indeed, the lowering of the surface tension facilitates the inflation of the lungs, but according to Laplace's law small and large alveoli are not in pressure equilibrium as long as the surface tension is equal in both small and large alveoli. In the present work, we tried to stabilize the lungs and to compare the effect of bolus surfactant substitution with the two-step substitution of fluorocarbons and surfactant. In all, 24 fetal immature lungs were used. For our experiments we used fluorocarbon 72 (FC-72) with a surface tension of 12 mN/m. In groups 1 and 2, a mixture of dipalmitoylphosphatidylcholine (DPPC): cholesterol 9:1 (molar ratio) or DPPC: phosphatidylglycerol (PG) 9:1 (molar ratio) was administered intratracheally as a bolus. In the case of groups 3 and 4, the immature lungs were rinsed first with FC-72. After removing the fluorocarbon, the lungs were artificially ventilated and the DPPC: cholesterol 9:1 (group 3) or DPPC:PG 9:1 mixture (group 4) was given in aerosol form. Static pressure-volume curves (p-v) of the mean values of the 6 lungs in each group were registered at the beginning (0 min) and after 20 and 40 min of artificial ventilation. Airway opening pressure, weight-specific end-inspiratory lung compliance, and phospholipid contents were investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1991

Empirical evidence against the 'cycle time dependency' assumption.

The interpretation of the 'cardiac cycle time effect', also named 'time-dependent primary bradycardia' by the Laceys, who first observed it, has been controversial in psychophysiology. Unconfounded evidence for the dependence of a vagal effect of psychological stimuli on time of stimulation within the cardiac cycle has been missing to date. An experiment in which the subjects could not anticipate the occurrence of the stimuli (short tones of a specific frequency that had to be counted) was performed. The data reduction procedure secured unambiguous interpretation of the data with respect to time-dependency or no time-dependency. No indication of any kind of cycle time dependency of the vagal effect was found.

Acoustic Stimulation↗
PubMed1991

Motile responses of vestibular hair cells following caloric, electrical or chemical stimuli.

Isolated, living vestibular hair cells (VHCs) from the guinea pig are capable of producing self-movements. Current injections and extracellular alternating current (a.c.) fields evoked mechanical responses of cell body or sensory hairs. Furthermore, superfusion in the presence of kainic acid or slow depolarizations by K-/gluconate evoked reversible slow motile responses of solitary vestibular sensory cells. If present in vivo, active VHC mechanics will influence the mechano-sensitive stereocilia and modulate stiffness and compliance of the receptor structure and its cupular or macular relationship. A tonic VHC motility might directly influence the displacement configuration in the cupula and macula organs and thus the micromechanical operating conditions of these sensory organs. Active mechanical events could contribute to adaptation processes (automatic gain control) and micromechanical non-linearities of stereociliary displacements. In addition, we demonstrate that direct caloric stimulation of isolated, living type I VHCs from guinea pig elicited mechanical responses of the sensory cells. This mechanism could contribute to the caloric induction of a nystagmus both under terrestrial and microgravitational conditions.

Animals↗