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U Zimmermann

Publications and source records attributed to U Zimmermann.

At least 145 records · Page 8Linked to original sources
PubMed1994

Specific glutathione-SH inhibition of toxic effects of metabolized gentamicin on isolated guinea pig hair cells.

The present investigation has shown that only metabolized gentamicin (mG) but not native gentamicin (G) is cytotoxic for isolated guinea pig outer hair cells (OHC). Using FURA-2 fluorescence, both G and mG were found to reduce intracellular free Ca2+ concentrations in unstimulated OHC and inhibit increases in intracellular Ca2+ concentrations during K(+)-induced depolarization. Glutathione-SH (GSH), a detoxificating agent, did not interfere with G and mG effects on intracellular Ca2+ concentration. In non-stimulated OHC, mG but not G induced pathological OHC depolarization, indicating the opening of transduction channels to allow influx of K+ ions. GSH completely inhibited the lytic effect of mG. Electrophysiological investigations also revealed that GSH probably inhibits mG-induced pathological opening of transduction channels. These results suggest that GSH selectively inhibits mG-specific toxic effects on the guinea pig OHC, possibly by enzymatic detoxification.

Animals↗
PubMed1994

Transitory endolymph leakage induced hearing loss and tinnitus: depolarization, biphasic shortening and loss of electromotility of outer hair cells.

There are types of deafness and tinnitus in which ruptures or massive changes in the ionic permeability of the membranes lining the endolymphatic space [e.g., of the reticular lamina (RL)] are believed to allow potassium-rich endolymph to deluge the low [K+] perilymphatic fluid (e.g., in the small spaces of Nuel). This would result in a K+ intoxication of sensory and neural structures. Acute attacks of Ménière's disease have been suggested to be an important example for this event. The present study investigated the effects of transiently elevated [K+] due to the addition of artificial endolymph to the basolateral cell surface of outer hair cells (OHC) in replicating endolymph-induced K+ intoxication of the perilymph in the small spaces of Nuel. The influence of K+ intoxication of the basolateral OHC cell surface on the transduction was then examined. Intoxication resulted in an inhibition of the physiological repolarizing K+ efflux from hair cells. This induced unwanted depolarizations of the hair cells, interfering with mechanoelectrical transduction. A pathological longitudinal OHC shortening was also found, with subsequent compression of the organ of Corti possibly influencing the micromechanics of the mechanically active OHC. Both micromechanical and electrophysiological alterations are proposed to contribute to endolymph leakage induced attacks of deafness and possibly also to tinnitus. Moreover, repeated or long-lasting K+ intoxications of OHC resulted in a chronic and complete loss of OHC motility. This is suggested to be a pathophysiological basis in some patients with chronic hearing loss resulting from Ménière's syndrome.

Action Potentials↗
PubMed1994

Electromotility of outer hair cells from the cochlea of the echolocating bat, Carollia perspicillata.

Isolated outer hair cells (OHCs) and explants ot the organ of Corti were obtained from the cochlea of the echolocating bat, Carollia perspicillata, whose hearing range extends up to about 100 kHz. The OHCs were about 10-30 microns long and produced resting potentials between -30 to -69 mV. During stimulation with a sinusoidal extracellular voltage field (voltage gradient of 2 mV/microns) cyclic length changes were observed in isolated OHCs. The displacements were most prominent at the level of the cell nucleus and the cuticular plate. In the organ of Corti explants, the extracellular electric field induced a radial movement of the cuticular plate which was observed using video subtraction and photodiode techniques. Maximum displacements of about 0.3-0.8 microns were elicited by stimulus frequencies below 100 Hz. The displacement amplitude decreased towards the noise level of about 10-30 nm for stimulus frequencies between 100-500 Hz, both in apical and basal explants. This compares well with data from the guinea pig, where OHC motility induced by extracellular electrical stimulation exhibits a low pass characteristic with a corner frequency below 1 kHz. The data indicate that fast OHC movements presumably are quite small at ultrasonic frequencies and it remains to be solved how they participate in amplifying and sharpening cochlear responses in vivo.

Animals↗
PubMed1994

DNA, protein, and plasma-membrane incorporation by arrested mammalian cells.

Incorporation of DNA, protein, and plasma membrane during blockage by aphidicolin or by doxorubicin was studied by flow cytometry and electrorotation of three cell lines (mouse-myeloma Sp2/0-Ag14, hybridoma H73C11, and fibroblast-like L929 cells). Drug-mediated arrest at the G1-S boundary (aphidicolin) or in G2/M (doxorubicin) did not arrest synthesis of either protein or total membrane area, the increases in which outstripped growth in cell volume and apparent cell area, respectively. Measurements of membrane capacity in normal and hypo-osmotic media showed that the drugs had not changed the fundamental bilayer, but that an increase in the number or size of microvilli must have occurred. Aphidicolin-arrested cells withstood hypo-osmotic stress better than untreated cells could, indicating that the membrane excess can be utilized as a reserve during rapid cell expansion. Hypo-osmotically treated cell populations exhibited only about half the coefficient of variance (CV) in membrane properties of cells at physiological osmolality. Populations of arrested cells exhibited the same high CV as asynchronous cells, indicating that chemical arrest does not give uniformly villated cell populations. However, the lowest CV values were given by some synchronized (aphidicolin-blocked, then released) populations. Removal of aphidicolin allowed most cells to progress through S and G2, and then divide. During these processes, the membrane excess was reduced. After removal of doxorubicin, the cells did not divide: some continued protein synthesis, grew abnormally large, and further increased their membrane excess. Membrane breakdown by electric pulsing (3 x 5kV/cm, 40 microseconds decay time) of aphidicolin-synchronized L cells in G2/M led to a 22% loss of plasma membrane (both the area-specific and the whole-cell capacitance were reduced), presumably via endocytosis-like vesiculation.

Animals↗
PubMed1994

Radio-frequency microtools for particle and liver cell manipulation.

Single particles can be manipulated by applying high frequencies to ultramicro electrode arrays fabricated on planar structures. Heat production can be reduced to the extent that intense electric fields can be applied even to unmodified cell culture media. Animal cells grow normally in the high field (up to 100 kV/m) between such continuously energized multielectrodes. As with laser tweezers [1-3], this technique can capture particles and cells in field traps, generate linear movement, and permit cell cultivation. It can also produce micropatterns of pH gradients, field-cast objects, and control cell adhesion. These microtools may be combined to develop cell separators, microsensors, and controlled-biocompatibility surfaces.

Animals↗
PubMed1994

Contribution of electrogenic ion transport to impedance of the algae Valonia utricularis and artificial membranes.

The cell membrane of Valonia utricularis contains an electrogenic carrier system for chloride (Wang et al., Biophys J. 59:235-248 (1991)). The electrical impedance of V. utricularis was measured in the frequency range between 1 Hz and 50 kHz. The analysis of the impedance spectra from V. utricularis and its comparison with equivalent circuit models showed that the transport system created a characteristic contribution to the impedance in the frequency range between 10 Hz and 5 kHz. The fit of the impedance spectra with the formalism derived from the theory of carrier-mediated transport allowed the determination of the kinetic parameters of chloride transport through the cell membrane of V. utricularis, and its passive electrical properties. Simultaneous measurements of the kinetic parameters with the charge pulse method demonstrated the equivalence of both experimental approaches with respect to the evaluation of the translocation rate constants of the free and the charged carriers and the total density of carriers within the membrane. Moreover, the impedance spectra of the protonophor-mediated proton transport by FCCP (carbonylcyanide p-trifluoromethoxyphenyl-hydrazone) were measured in model membranes. The carrier system made a substantial contribution to the impedance of the artificial membranes. The analysis of the spectra in terms of a simple carrier system (Benz and McLaughlin, 1983, Biophys. J. 41:381-398) allowed the evaluation of the kinetic and equilibrium parameters of the FCCP-mediated proton transport. The possible application of the measurement of impedance spectra for the study of biological transport systems is discussed.

Biological Transport↗
PubMed1994

Large-scale production of Ba(2+)-alginate-coated islets of Langerhans for immunoisolation.

Islet xenografts immunisolated in alginate capsules have been proposed by many groups for clinical islet transplantation. However, diffusion limitations and the total volume of microcapsules required for transplantation are, among other things, factors which have so far prevented successful clinical application. In this study, these problems have been overcome by immobilisation of rat and porcine islets in a Ba(2+)-cross-linked alignate matrix using an air jet droplet generator technique in combination with subsequent density-gradient purification. This procedure leads to high yields of islets coated with a tailored, thin layer of cross-linked alginate which protects the islets against cytotoxic compounds present in human plasma. The recovery of encapsulated rat and porcine islets was about 70%. Empty capsules were nearly completely removed. Using this technique, the total volume of the resulting microcapsules increased only by a factor of about 1.5 compared to the volume of free islets. The technique can be used for large-scale production of coated islets.

Alginates↗
PubMed1993

Characterization of the chloride carrier in the plasmalemma of the alga Valonia utricularis: the inhibition by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid.

The effect of the anion transport inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) on the Cl(-)-transport system located in the plasmalemma of cells of the giant marine alga Valonia utricularis was studied by using the charge pulse relaxation technique. Analysis of the biphasic relaxation patterns in terms of the kinetic model published previously (Wang, J., Wehner, G., Benz, R. and Zimmermann, U. (1991) Biophys. J. 59, 235-248) demonstrated that extracellular DIDS dramatically reduced the translocation rate, KAS, of the Cl(-)-carrier complex (maximal inhibition 79%). The translocation rate of the free carrier molecules, KS, as well as the total surface concentration of the carrier, No, were not affected. A Hill-plot of DIDS inhibition on KAS yielded an half-maximal inhibition concentration (IC50) of 3.9 x 10(-5) M and Hill-coefficient of 1.61, suggesting a co-operative binding of the inhibitors to the Cl(-)-carrier. The maximal inhibition of DIDS was dependent on the extracellular Cl(-)-concentration. This inhibition was not competitive to chloride, since it increased and did not decrease with increasing chloride concentration. The DIDS effect decreased with increasing pH-value (investigated pH range between 6.5 and 10). Intravascular DIDS or SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid) had no effect on the biphasic voltage relaxation pattern. These results showed that the binding sites of DIDS must be located on the outer surface of the plasmalemma of V. utricularis and, in turn, supported previous conclusions that the Cl(-)-carrier (which is assumed to be part of the turgor-pressure-sensing mechanism) is only located in the outer membrane.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

Dielectric measurements on electro-manipulation media.

The permittivity and conductivity of solutions of sugars and sugar alcohols, such as are suitable for electric-field work on cells, were measured. The range of concentrations was 0-3 M (subject to solubility), and the frequency range was that commonly used in dielectrophoresis prior to electrofusion (200 kHz-2 MHz). This was widened to 30 kHz-12 MHz, when dispersive behaviour was found. A parallel-plate impedance chamber with variable electrode-spacing, suited to stable measurements in these low-conductivity aqueous media, was used. Errors due to electrode polarisation were effectively removed by linear regression of the series parameters against electrode distance, as well as by subtraction of data obtained on KCl solutions of comparable conductivity. The permittivity of the sugar solutions decreased as only approximately linear functions of concentration, so that a description in terms of both first- and second-order molar dielectric increments (delta 1 and delta 2) provided a better description of the behaviour than a single linear increment (delta). Sugar solutions of concentration of 1.2 M or less showed no change in permittivity or conductivity over the measured frequency range (i.e., were dispersion-free). On the other hand, various high-density media showed dispersion. The stabilised silica sol 'Percoll' showed dispersion over the whole frequency range; solutions of sucrose (at above 1.2 M concentration), as well as of proprietary high-density solutes ('Metrizamide' at above 0.5 M and 'Nycodenz' at above 0.75 M) showed dispersion above 0.6 MHz. Although these media are of interest for electro-manipulation (they can be used to prevent sedimentation), their dispersive properties may make them unsuitable for use with radio-frequency fields.

Carbohydrates↗
PubMed1993

A traveling-wave micropump for aqueous solutions: comparison of 1 g and microgram results.

The operation of a micro-chip-based fluid circulator based on the interaction of a high-frequency traveling wave with a thermally generated inhomogeneity in an aqueous medium is investigated. The profiles of the electric field, the thermal gradient and the driving force within the device are derived numerically, and the dependence upon applied voltage under different experimental conditions is derived. The importance of convection in the operation of the device is assessed by operating it in various orientations, as well as under microgravity, and also by investigating the reversal and turn-on characteristics. The pump showed the unexpected ability to trap microparticles present in the driven fluid.

Electricity↗
PubMed1993

Hypotonically induced changes in the plasma membrane of cultured mammalian cells.

Cells from three cell lines were electrorotated in media of osmotic strengths from 330 mOsm to 60 mOsm. From the field-frequency dependence of the rotation speed, the passive electrical properties of the surfaces were deduced. In all cases, the area-specific membrane capacitance (Cm) decreased with osmolality. At 280 mOsm (iso-osmotic), SP2 (mouse myeloma) and G8 (hybridoma) cells had Cm values of 1.01 +/- 0.04 microF/cm2 and 1.09 +/- 0.03 microF/cm2, respectively, whereas dispase-treated L-cells (sarcoma fibroblasts) exhibited Cm = 2.18 +/- 0.10 microF/cm2. As the osmolality was reduced, the Cm reached a well-defined minimum at 150 mOsm (SP2) or 180 mOsm (G8). Further reduction in osmolality gave a 7% increase in Cm, after which a plateau close to 0.80 microF/cm2 was reached. However, the whole-cell capacities increased about twofold from 200 mOsm to 60 mOsm. L-cells showed very little change in Cm between 280 mOsm and 150 mOsm, but below 150 mOsm the Cm decreased rapidly. The changes in Cm correlate well with the swelling of the cells assessed by means of van't Hoff plots. The apparent membrane conductance (including the effect of surface conductance) decreased with Cm, but then increased again instead of exhibiting a plateau. The rotation speed of the cells increased as the osmolality was lowered, and eventually attained almost the theoretical value. All measurements indicate that hypo-osmotically stressed cells obtain the necessary membrane area by using material from microvilli. However, below about 200 mOsm the whole-cell capacities indicate the progressive incorporation of "extra" membrane into the cell surface.

Animals↗
PubMed1993

Lymphoid activation by micro- and macroencapsulated islets during mixed lymphocyte islet culture.

We have recently demonstrated long-lasting normoglycaemia after transplantation of barium alginate microencapsulated rat and porcine islets. Nevertheless the transplantation results obtained with different microencapsulation techniques have been controversial. Little is known about possible immune interactions between host and encapsulated islet. This study demonstrates in vitro stimulation of lymphoid cells by encapsulated islets that is similar to that of unencapsulated islets. This stimulation was reduced by a 4-day culture with unencapsulated islets only. After macroencapsulation of islets in hollow fibres a stimulatory effect was also observed, but this was less pronounced than after microencapsulation. Empty microcapsules as well as macrocapsules induced lymphoid proliferation as a result of mitogenic impurities in the encapsulation materials themselves. In the same donor-recipient combination in which we have shown successful transplantation, we found activation of the sensibilization arm of the immune system. This suggests that microencapsulation results in protection of the transplanted islets from the action of the effector arm. This lymphoid activation could be triggered by the mitogeniticity of the encapsulation material itself. In the case of alginates these mitogenic factors could not be abolished by culture (i.e. dialysis).

Alginates↗
PubMed1993

Electrofusion.

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Animals↗
PubMed1993

Kinetics of pore size during irreversible electrical breakdown of lipid bilayer membranes.

The kinetics of pore formation followed by mechanical rupture of lipid bilayer membranes were investigated in detail by using the charge-pulse method. Membranes of various compositions were charged to a sufficiently high voltage to induce mechanical breakdown. The subsequent decrease of membrane voltage was used to calculate the conductance. During mechanical breakdown, which was probably caused by the widening of one single pore, the membrane conductance was a linear and not exponential function of time after the initial starting process. In a large number of experiments using various lipids and electrolytes, the characteristic opening process of the pore turned out to be independent of the actual membrane potential and electrolyte concentration. Our theoretical analysis of the pore formation suggested that the voltage-induced irreversible breakdown is due to a decrease in edge energy when the pore had formed. After initiation of the pore, the electrical contribution to surface tension is negligible. The time course of the increase of pore size shows that our model of the irreversible breakdown is in good agreement with mechanical properties of membranes reported elsewhere.

Biophysical Phenomena↗