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Biomedical subjects

U Zimmermann

Publications and source records attributed to U Zimmermann.

At least 235 records · Page 13Linked to original sources
PubMed1985

[The isolated living hair cell. A new model for the study of hearing function].

Living, predominantly outer hair cells were prepared from the guinea pig cochlea using a non-enzymatic, microsurgical approach. Viability of hair cells was demonstrated by dye-exclusion as well as by electrophysiogical patch-damp procedures. This allowed to measure a mammalian hair cell potential of -70 mV under direct visualisation. Furthermore, hair cells could be kept under cell culture conditions for 6-9 hrs. Isolated, mammalian cochlea hair cells are a new, useful model to investigate the molecular basis of hearing and hearing disorders located in sensory cells. As example this report shows experimental approaches to analyse membraneous and cytoplasmic functions of hair cells.

Animals↗
PubMed1984

Magneto-electro-fusion of human erythrocytes.

In inhomogeneous (static) magnetic fields close contact between 'magnetic' human erythrocytes was established. The cells were made magnetic by incubating them in a medium containing small Fe3O4 -particles which adsorbed to the outer membrane surface. Fusion was induced by applying two electric field pulses (field strength: 8.5 kV X cm-1; duration: 60 microseconds) to the magnetically collected cells. This procedure allowed the use of electrically conductive media (3 X 10(-3) omega -1 X cm-1). Fusion of red blood cells occurred very often. If cell suspensions of high density were used fusion resulted in the formation of giant red blood cells with osmotically intact membranes.

Erythrocyte Membrane↗
PubMed1984

Electro-fusion of cells: principles and potential for the future.

Exposure of cells or liposomes to a brief pulse of a strong electrical field can result in a reversible breakdown of the outer membrane. Such breakdown results in an increase in permeability of the plasmalemma, which however re-seals after a short incubation (i.e. the original impermeability is restored). Two or more cells in contact can be made to fuse by this process, provided that the contact is close enough and that the pulse of the electrical field is short enough not to damage the cells. Methods of achieving this contact by electrical and magnetic fields are described. The magnetic method does not demand the use of the low conductivity media used earlier. Other possible modifications of this flexible technique are also described, and used to show how the technique can be modified in future, and how it may be applied to the fields of membrane research, medicine and plant breeding.

Animals↗
PubMed1983

Electrofusion of myeloma cells on the single cell level. Fusion under sterile conditions without proteolytic enzyme treatment.

A technique is presented which allows electrofusion of single cells under sterile conditions. The electrofusion chamber is placed in a Petri dish. Before a droplet of the fusion medium is pipetted between the electrodes, the chamber is completely covered with vaseline, which prevents the fusion medium evaporating. Additionally, the fusion chamber is treated with solutions containing poly(L)-lysine and pronase which results in a decreased movement of the cells on the glass between the electrodes and which allows electrofusion without any proteolytic pretreatment.

Animals↗
PubMed1983

Evidence for the presence of mobile charges in the cell membrane of Valonia utricularis.

Charge-pulse relaxation studies were performed on cells of the giant marine alga Valonia utricularis with microelectrodes inserted into the vacuole. If the cell was charged by short pulses of 200 ns duration, the decay of the initial membrane voltage could be described by two relaxation processes at normal pH (8.2). The fast exponential relaxation had a time constant of approximately 100 microseconds whereas the the time constant of the slow relaxation ranged between 2 and 15 ms. The ratio of the two amplitudes varied between 10 and 20 and was found to be independent of the initial voltage, up to 400 mV. In contrast to the time constants, the amplitude ratio was a function of the duration of the charge pulse. As the pulse length was increased to 10 ms, the fast relaxation disappeared. A change in pH of the natural sea water from 8.2 to 4 resulted in the disappearance of both exponential processes and the appearance of one single exponential with a 1-ms time constant over the whole pulse-length range. The analysis of the data in terms of a two-membrane model leads to unusual values and a pH-dependence of the specific capacitances (0.6 and 6 microF cm-2) of the two membranes, which can be treated as two serial circuits of a capacitor and a resistor in parallel. The charge-pulse and the current-clamp data are consistent with the assumption that the cell membrane of V. utricularis contains mobile charges with a total surface concentration of approximately 4 pmol cm-2. These charges cross the membrane barrier with a translocation rate constant around 500 s-1 and become neutralized at low pH. From our experimental results it cannot be completely excluded that the tonoplast has also a high specific resistance. But in this case it has to be assumed that the tonoplast and plasmalemma have very similar electrical properties and contain both mobile charges, so that the two membranes appear as a single membrane. Experiments on artificial lipid bilayer membranes in the presence of the lipophilic ion dipicrylamine, support our mobile charge concept for the cell membrane of V. utricularis.

Cell Membrane↗
PubMed1983

[Staining behavior and applicability of spectrally pure Capriblue GN, Stella Blue, Oxonin and Punky Blue].

The staining properties of 4 spectral pure derivates of Phenoxazin--Capriblue GN, Stella Blue, Oxonin, and Punky Blue--were investigated using human and animal tissues. Punky Blue and Stella Blue are newly synthesized derivates. A simplified staining technique was developed based on conventional fixing and mounting methods of histological materials. Punky Blue is a particularly contrasting metachromatic nucleus stain, and produces at pH = 4 and a staining period of 5 min a differentiated cell picture, the colours of which are comparable to conventional stains. The Oxonin-stain produces good contrasts after 2 min. Capriblue GN is only limited use as one-component tissue stain, due of its low metachromatic characteristics and Stella Blue, on its own, does not provide sufficient contract. The influence of electrolytes and hydrogen ions on the staining mechanisms will be discussed. An increase of hydrogen ions is used to control the selective staining of amphoteric biopolymers. The possible binding mechanisms of stains used are discussed in the light of their staining properties.

Chemical Phenomena↗
PubMed1982

Rotation of cells in an alternating electric field: theory and experimental proof.

Protoplasts of Avena sativa rotate in an alternating electric field provided that at least two cells are located close to each other. An optimum frequency range (20 to 30 kHz) exists where rotation of all cells exposed to the field is observed. Below and above this frequency range, rotation of some cells is only occasionally observed. The angular velocity of rotation depends on the square of the electric field strength. At field strengths above the value leading to electrical breakdown of the cell membrane, rotation is no longer observed due to deterioration of the cells. The absolute value of the angular velocity of rotation at a given field strength depends on the arrangement of the cells in the electric field. A maximum value is obtained if the angle between the field direction and the line connecting the two cells is 45 degrees. With increasing distance between the two cells the rotation speed decreases. Furthermore, if two cells of different radii are positioned close to each other the cell with the smaller radius will rotate with a higher speed than the larger one. Rotation of cells in an alternating electric field is described theoretically by interaction between induced dipoles in adjacent cells. The optimum frequency range for rotation is related to the relaxation of the polarization process in the cell. The quadratic dependence of the angular velocity of rotation on the field strength results from the fact that the torque is the product of the external field and the induced dipole moment which is itself proportional to the external field. The theoretical and experimental results may be relevant for cyclosis (rotational streaming of cytoplasm) in living cells.

Cell Membrane↗
PubMed1982

A new method for the determination of hydraulic conductivity and cell volume of plant cells by pressure clamp.

Internodes of Chara corallina were used for experiments in which cell turgor pressure was clamped by means of the pressure probe technique. Essentially, the procedure consisted of a combination of volume and turgor pressure relaxations. This technique permits the determination of the cell volume by nonoptical means. The values obtained are in agreement with the ones determined by optical means. Furthermore, the hydraulic conductivity (L(p)) was determined from the initial slope of the volume relaxation; the values thus obtained are in agreement with those calculated from the half-times of pressure relaxations. The determination of L(p) from volume relaxation measurements has the advantage that the cell volume, the volumetric elastic modulus of the cell wall, and the internal osmotic pressure do not have to be known. Furthermore, the half-time of volume relaxation is longer than that of pressure relaxation, as shown by theory and experiment. This may be used to enhance the resolution of the relaxation measurement and, thus, to improve the accuracy of L(p) determinations for higher plant cells which exhibit a very fast pressure relaxation.

Journal Article↗