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Biomedical subjects

U Zimmermann

Publications and source records attributed to U Zimmermann.

At least 217 records · Page 12Linked to original sources
PubMed1987

Influence of anaesthetics on the movement of the mobile charges in the algal cell membrane of Valonia utricularis.

Voltage relaxation studies in the presence of anaesthetics were performed on cells of the giant marine alga Valonia utricularis using intracellular microelectrodes. From the decay of the initial membrane voltage which can be described by two relaxation processes the conclusion can be drawn that protein-linked, mobile charges are present which are probably involved in turgor-pressure-dependent potassium transport (Büchner, K.-H., Rosenheck, K. and Zimmermann, U. (1985) J. Membrane Biol. 88, 131-137). The anaesthetics halothane and chloroform were found to affect reversibly, procaine and tetracaine irreversibly the translocation rate k of the mobile charges at concentrations which were equal to (for halothane and chloroform) or significantly below (for procaine and tetracaine) clinical and nerve blocking levels. The concentration of the mobile charges Nt as well as the specific membrane resistance Rm and the specific membrane capacitance Cm remained unchanged in these concentration ranges. The data suggest a specific interaction of anaesthetics with specialized target sites of a transport protein to which the mobile charges are coupled.

Anesthetics↗
PubMed1987

Proteases and antiproteases related to the coagulation system in plasma and ascites--an approach to differentiate between malignant and cirrhotic ascites.

The concentrations of several proteases and antiproteases known to be present in ascites were tested in plasma and ascitic fluid with regard to their ability to separate ascites according to malignant or nonmalignant disease. Seventeen patients with proven malignant ascites and 37 with ascites due to liver cirrhosis were included. Activities of plasminogen, alpha 2-antiplasmin, antithrombin-III, and factor V, and the concentration of alpha 1-protease inhibitor were significantly higher in the plasma of patients with malignant ascites than in cirrhotic patients. Fibronectin, plasminogen, alpha 2-macroglobulin, alpha 1-protease inhibitor, antithrombin-III, and albumin revealed higher concentrations or activities in malignant ascites than in cirrhotic ascites. Due to a wide variation of most parameters, only fibronectin, antithrombin III, and alpha 1-protease inhibitor in ascites had a sensitivity and specificity higher than 90% for malignant ascites. When the specific protein/albumin ratio was used, only the accuracy of fibronectin was increased reaching a sensitivity and specificity of 100%. The plasma/ascites gradients of the proteins assessed differed significantly, that of fibronectin being much higher (22 +/- 7) than that of all other proteins. In malignant ascites fibronectin concentration was only correlated with alpha 1-protease inhibitor concentration but not with the concentration or activity of all other proteins, while in cirrhotic ascites most proteins revealed a positive correlation. The determination of the fibronectin concentration or the fibronectin/albumin ratio in ascites can differentiate malignant and nonmalignant ascites. All other proteases and antiproteases assessed are of lesser value for this purpose, although most are significantly increased in ascites and plasma of patients with malignant disorders.

Antithrombin III↗
PubMed1987

Proteases and antiproteases related to the coagulation system in plasma and ascites--influence of dexamethasone.

Fibrinolysis induced by the infusion of plasminogen activators into the circulation has been shown to cause coagulation disorders in ascites retransfusion. Dexamethasone is known to inhibit the synthesis of plasminogen activators by peritoneal macrophages. We therefore assessed its potential in preventing the occurrence of fibrinolysis by injecting 16 mg dexamethasone intraperitoneally in 10 patients 24 h before ascites retransfusion was performed. In addition, the effect of dexamethasone upon the activity or concentration of several proteases and antiproteases related to coagulation in plasma and ascites was analyzed on 15 occasions. An increase of the activity of plasminogen, alpha 2-antiplasmin, and antithrombin III, and in the concentration of alpha 1-protease inhibitor in ascites was induced by the dexamethasone injection. However, the reaction was not identical in all patients. Those patients having an increase of plasminogen activities of 0.6 CTA U/ml or more did not show signs of fibrinolysis during retransfusion. The results obtained indicate that intraperitoneal injection of dexamethasone decreases the concentration of plasminogen activators in ascites and thereby reduces the risk of coagulation disorders during retransfusion procedures. Since the effect is variable and not sustained, assessment of preoperative plasminogen concentrations is mandatory in order to prevent complications.

Antithrombin III↗
PubMed1987

Large scale transfection of mouse L-cells by electropermeabilization.

Mouse L-cells were transfected by electropermeabilization using the selectable plasmid pSV2-neo which confers resistance to G-418 (Geneticin). The DNA concentration used was 1 microgram/ml, the field strength was 10 kV/cm, the duration of the pulse was 5 microseconds. Transfection yield was optimal at a temperature of 4 degrees C when using a time in between consecutive pulses of 1 minute compared to shorter (of the order of seconds) or longer (3 minutes) time intervals. A more detailed study of the relationship between the number of pulses applied (up to 10) and transfection yield showed it to be almost linear in this range at 4 degrees C. The yield of transfectants in response to 10 pulses was up to 1000 per 10(6) cells (using 3.3 pg DNA per cell). The influence of the growth phase of the cells on the transfection yield and/or the subpopulation of the mouse L-cell line used was shown. Furthermore the clone yield depended on the DNA per cell ratio within a very small range.

Animals↗
PubMed1987

The effect of mercuric salts on the electro-rotation of yeast cells and comparison with a theoretical model.

The rotational spectrum of yeast cells changed after pre-treatment of the cells with HgCl2 or Hg(NO3)2 and became indistinguishable from that of ultrasonically produced cell walls. The spectrum of the affected cells contained a peak which could only be explained by attributing a conductivity to the cell walls that was higher than that of the medium. Theoretical models of the rotational response are fully in accord with the experimental spectra. It is shown that the rotation method is capable of measuring even the low cell wall conductivity of yeast cells (which was found to be 33 microS/cm at 10 microS/cm medium conductivity). Knowledge of the spectra allowed a field frequency to be selected at which untreated cells showed no rotation, but at which cells affected by treatment with Hg(II) identified themselves by rotating in the same direction as the field. Calculation of the percentage of cells showing this co-field rotation gave an index (termed the co-field rotation value) of the proportion of the cells that were affected. Using this technique, effects of 25 nmol/l Hg(II) could be demonstrated. In media of low conductivity (10 microS/cm) the change in the rotational spectrum was usually 'all-or-none', whereas at 200 microS/cm a graded Hg(II)-mediated change became apparent. The co-field rotation method showed that the action of small quantities of Hg(II) was still increasing after 3 h of incubation and paralleled the Hg(II)-induced K+ release. A rapid reduction of the effects of Hg(II) was seen when 3-30 mM K+ (or Na+) or when 1 mM Ca2+ were present in the incubation medium, or as the pH was increased. At high incubation cell concentrations the toxic effect of Hg(II) was reduced, apparently due to binding by the cells.

Calcium↗
PubMed1986

Assay of photosynthetic oxygen evolution from single protoplasts.

A semiquantitative assay for light-dependent O(2) evolution by a single mesophyll protoplast is described. The assay indicator is the density of aerotactic bacteria (Pseudomonas aeruginosa, ATCC 10145; ;Engelmann experiment') attracted to the protoplast. Quantification is by dark field microphotometry. The sensitivity is about 50 femtomoles O(2) per protoplast per minute. The results demonstrate the biphasic nature of O(2) evolution of a single protoplast during photosynthetic induction. Computerized data acquisition yields traces which, until a steady state of photosynthetic O(2) evolution is reached, are identical to ordinary O(2) electrode traces.

Journal Article↗
PubMed1986

Receptor patching and capping of platelet membranes induced by monoclonal antibodies.

Redistribution of glycoproteins (GP) Ib, glycocalicin, IIb, and IIIa on the surface of human platelets in response to stimulation with corresponding monoclonal antibodies (MoAb) and a polyclonal antiglycocalicin antibody was studied by immunofluorescence, immunoelectron microscopy, and a quantitative radioimmune assay. Immobilization of the antigens by prefixation with formaldehyde showed a uniform distribution over the surface of the platelet. Incubation of unfixed platelets with specific MoAb against various epitopes on GPIIb and/or IIIa resulted in a time-dependent patching, subsequent capping, and after prolonged exposure to the antibody/label complex, internalization of the complex, possibly by endocytosis. In contrast, GPIb could not be shown to cap. From these results we conclude that platelet GPIIb and/or IIIa undergo spatial rearrangement in a manner analogous to that observed in lymphocytes, whereas GPIb does not. Since both GPIb and GPIIb and/or IIIa seem to be transmembraneous GP associated with the cytoskeleton, a special, though unidentified, role of GPIIb/IIIa in the induction of lateral membrane mobility is postulated.

Antibodies, Monoclonal↗
PubMed1985

Electro-acoustic fusion of erythrocytes and of myeloma cells.

Mammalian cells can be concentrated in a sound field. A method is introduced, which combines the reversible aggregation of cells in a sound field with the electrical breakdown of cell membranes to fuse cells, which are in contact. Human red blood cells and mouse myeloma cells are fused by means of that procedure.

Animals↗
PubMed1985

Determination of intracellular conductivity from electrical breakdown measurements.

The intracellular resistivity (conductivity) of cells can be easily calculated with high accuracy from electrical membrane breakdown measurements. The method is based on the determination of the size distribution of a cell suspension as a function of the electrical field strength in the orifice of a particle volume analyser (Coulter counter). The underestimation of the size distribution observed beyond the critical external field strength leading to membrane breakdown represents a direct access to the intracellular resistivity as shown by the theoretical analysis of the data. The potential and the accuracy of the method is demonstrated for red blood cells and for ghost cells prepared by electrical haemolysis. The average value of 180 omega X cm for the intracellular resistivity of intact red blood cells is consistent with the literature.

Cytoplasm↗
PubMed1985

An improved electrofusion technique for production of mouse hybridoma cells.

An experimental procedure is described for the reproducible production of hybridoma cells using the electrofusion technique. High yields can be obtained when fusion is performed in isotonic inositol solutions containing Ca2+ and Mg2+ in a ratio of 1:5 in the millimolar range. The hybridoma cells are transferred 10 min after the field pulse application into a balanced salt solution for 30 min at 37 degrees C.

Animals↗
PubMed1985

Reversible contraction of isolated mammalian cochlear hair cells.

Outer hair cells were isolated from the guinea pig cochlea using a micromechanical non-enzymatic procedure. Depolarization of outer hair cells in the presence of 25-125 mM K+ was accompanied by a longitudinal contraction of the isolated cells. A decrease of [K+] to 5.4 mM interrupted contraction and induced a relaxation. Individual hair cells were able to undergo as many as 5 cycles of contraction and relaxation. External Ca2+ was required for relaxation of the contracted hair cells. The contractile event led to the production of a visible cytoplasmic network between the supranuclear area and the cuticular plate.

Actin Cytoskeleton↗