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U Zimmermann

Publications and source records attributed to U Zimmermann.

At least 73 records · Page 4Linked to original sources
PubMed1999

A patch-clamp study of ion channels in protoplasts prepared from the marine alga Valonia utricularis.

The giant marine alga Valonia utricularis is a classical model system for studying the electrophysiology and water relations of plant cells by using microelectrode and pressure probe techniques. The recent finding that protoplasts can be prepared from the giant "mother cells" (Wang, J., Sukhorukov, V.L., Djuzenova, C.S., Zimmermann, U., Müller, T., Fuhr, G., 1997, Protoplasma 196:123-134) allowed the use of the patch-clamp technique to examine ion channel activity in the plasmalemma of this species. Outside-out and cell-attached experiments displayed three different types of voltage-gated Cl(-) channels (VAC1, VAC2, VAC3, Valonia Anion Channel 1,2,3), one voltage-gated K(+) channel (VKC1, Valonia K(+) Channel 1) as well as stretch-activated channels. In symmetrical 150 mm Cl(-) media, VAC1 was most frequently observed and had a single channel conductance of 36 +/- 7 pS (n = 4) in the outside-out and 33 +/- 5 pS (n = 10) in the cell-attached configuration. The reversal potential of the corresponding current-voltage curves was within 0 +/- 4 mV (n = 4, outside-out) and 9 +/- 7 mV (n = 10, cell-attached) close to the Nernst potential of Cl(-) and shifted towards more negative values when cell-attached experiments were performed in asymmetrical 50:150 mm Cl(-) media (bath/pipette; E(Cl(-)) -20 +/- 7 mV (n = 4); Nernst potential -28 mV). Consistent with a selectivity for Cl(-), VAC1 was inhibited by 100 micronM DIDS (4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid). VAC1 was activated by a hyperpolarization of the patch. Boltzmann fits of the channel activity under symmetrical 150 mm Cl(-) conditions yielded a midpoint potential of -12 +/- 5 mV (n = 4, outside-out) and -3 +/- 6 mV (n = 9, cell-attached) and corresponding apparent minimum gating charges of 15 +/- 3 (n = 4) and 18 +/- 5 (n = 9). The midpoint potential shifted to more negative values in the presence of a Cl(-) gradient. VAC2 was activated by voltages more negative than E(Cl(-)) and was always observed together with VAC1, but less frequently. It showed a "flickering" gating. The single channel conductance was 99 +/- 10 pS (n = 6). VAC3 was activated by membrane depolarization and frequently exhibited several subconductance states. The single channel conductance of the main conductance state was 36 +/- 5 pS (n = 5). VKC1 was also activated by positive clamped voltages. Up to three conductance states occurred whereby the main conductance state had a single channel conductance of 124 +/- 27 pS (n = 6). In the light of the above results it seems to be likely that VAC1 contributes mainly to the Cl(-) conductance of the plasmalemma of the turgescent "mother cells" and that this channel (as well as VAC2) can operate in the physiological membrane potential range. The physiological significance of VAC3 and VKC1 is unknown, but may be related (as the stretch-activated channels) to processes involved in turgor regulation.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1999

Differential expression of trkB.T1 and trkB.T2, truncated trkC, and p75(NGFR) in the cochlea prior to hearing function.

Prior to the onset of hearing, synchronous cellular, neuronal, and morphogenetic processes participate in the development of a functional cochlea. We have studied the expression of different splice forms of trkB and trkC as well as p75(NGFR) in rat and mouse cochlea within this critical developmental period, using in situ hybridization, PCR, Northern blotting, and immunohistochemical analyses. An antibody to full-length trkB receptors proved to detect full-length trkB receptors as well as truncated trkB.T2 but not trkB. T1 isoforms. Full-length trkB and trkC isoforms as well as trkB.T2 but not trkB.T1 receptors were noted in cochlear neurons. A transient expression of trkB.T1 and trkB.T2 was observed at the epithelial-mesenchymal border of the spiral ligament during this time. A sequential appearance of trkB.T1, the low-affinity neurotrophin receptor p75(NGFR), and trkB.T2 in epithelial cochlear cells correlated with the formation of the inner sulcus of the organ. A differential expression of presumptive trkB.T2 in hair and supporting cells was observed concomitant with the maturation of the distinct innervation pattern of these cells. A gradual shift from p75(NGFR) to truncated trkC receptors in Pillar cells occurred during the formation of the tunnel of Corti. A distinct expression of full-length trkC correlated with the time of differentiation of the stria vascularis. Finally, an expression of trkB.T1 and trkB.T2 in oligodendrocytes, full-length trkB and trkC in nerve fibers, and p75(NGFR) in Schwann cells was noted at the glial interface of the VIIIth nerve during the establishment of the glial transition zone. These various transitory neurotrophin receptor expression patterns, which were related to final maturation processes of the cochlea, may provide new insights into the as yet obscure role of neurotrophin receptors in nonneuronal tissue.

Animals↗
PubMed1999

Resistivity of red blood cells against high-intensity, short-duration electric field pulses induced by chelating agents.

The interaction of human red blood cells (RBCs) with diethylenetriamine-pentaacetic acid (DTPA) or its Gd-complex (Magnevist, a widely used clinical magnetic resonance contrast agent containing free DTPA ligands) led to the following, obviously interrelated phenomena. (i) Both compounds protected erythrocytes against electrohemolysis in isotonic solutions caused by a high-intensity DC electric field pulse. (ii) The inhibition of electrohemolysis was observed only when cells were electropulsed in low-conductivity solutions. (iii) The uptake of Gd-DTPA by electropulsed RBCs was relatively low. (iv) (Gd-) DTPA reduced markedly deformability of erythrocytes, as revealed by the electrodeformation experiments using high-frequency electric fields. Taken together, the results indicate that (Gd-) DTPA produce stiffer erythrocytes that are more resistant to electric field exposure. The observed effects of the chelating agents on the mechanical properties and the electropermeabilization of RBCs must have an origin in molecular changes of the bilayer or membrane-coupled cytoskeleton, which, in turn, appear to result from an alteration of the ionic equilibrium (e.g., Ca(2+) sequestration) in the vicinity of the cell membrane.

Chelating Agents↗
PubMed1999

Electric field pulses can induce apoptosis.

Injection of electric field pulses of high intensity (kV/cm) and short duration (microsecond range) into a cell suspension results in a temporary increase of the membrane permeability due to a reversible electric breakdown of the cell membrane. Here we demonstrate that application of supercritical field pulses between 4. 5 and 8.1 kV/cm strength and 40 microsec duration induce typical features of apoptosis in Jurkat T-lymphoblasts and in HL-60 cells including DNA fragmentation and cleavage of the poly(ADP ribose) polymerase. Apoptosis induction did not depend on the presence of any particular electrolyte in the extracellular medium. However, no apoptosis was observed in solutions without a minimum amount of salt. Apoptotic DNA fragmentation was prevented by the caspase inhibitor zVAD.

Apoptosis↗
PubMed1999

Determination of the individual electrical and transport properties of the plasmalemma and the tonoplast of the giant marine alga Ventricaria ventricosa by means of the integrated perfusion/charge-pulse technique: evidence for a multifolded tonoplast.

The charge-pulse relaxation spectrum of nonperfused and perfused (turgescent) cells of the giant marine alga Ventricaria ventricosa showed two main exponential decays with time constants of approximately 0.1 msec and 10 msec, respectively, when the cells were bathed in artificial sea water (pH 8). Variation of the external pH did not change the relaxation pattern (in contrast to other giant marine algae). Addition of nystatin (a membrane-impermeable and pore-forming antibiotic) to the vacuolar perfusion solution resulted in the disappearance of the slow exponential, whereas external nystatin decreased dramatically the time constant of the fast one. This indicated (by analogy to corresponding experiments with Valonia utricularis, J. Wang, I. Spiess, C. Ryser, U. Zimmermann, J. Membrane Biol. 157: 311-321, 1997) that the fast relaxation must be assigned to the RC-properties of the plasmalemma and the slow one to those of the tonoplast. Consistent with this, external variation of [K+]o or of [Cl-]o as well as external addition of K+- or Cl--channel/carrier inhibitors (TEA, Ba2+, DIDS) affected only the fast relaxation, but not the slow one. In contrast, addition of these inhibitors to the vacuolar perfusion solution had no measurable effect on the charge-pulse relaxation spectrum. The analysis of the data in terms of the "two membrane model" showed that K+- and (to a smaller extent) Cl--conducting elements dominated the plasmalemma conductance. The analysis of the charge-pulse relaxation spectra also yielded the following area-specific data for the capacitance and the conductance for the plasmalemma and tonoplast (by assuming that both membranes have a planar surface): (plasmalemma) Cp = 0.82 * 10(-2) F m-2, Rp = 1.69 * 10(-2) Omega m2, Gp = 5.9 * 10(4) mS m-2, (tonoplast) Ct = 7. 1 * 10(-2) F m-2, Rt = 14.9 * 10(-2) Omega m2 and Gt = 0.67 * 10(4) mS m-2. The electrical data for the tonoplast show that (in contrast to the literature) the area-specific membrane resistance of the tonoplast of these marine giant algal cells is apparently very high as reported already for V. utricularis. The exceptionally high value of the area-specific capacitance could be explained - among other interpretations - by assuming a 9-fold enlargement of the tonoplast surface. The hypothesis of a multifolded tonoplast was supported by transmission electronmicroscopy of cells fixed under maintenance of turgor pressure and of the electrical parameters of the membranes. This finding indicates that the tonoplast of this species exhibited a sponge-like appearance. Taking this result into account, it can be easily shown that the tonoplast exhibits a high-resistance (1.1 Omega m2). Vacuolar membrane potential measurements (performed in parallel with charge-pulse relaxation studies) showed that the potential difference across the plasmalemma was mainly controlled by the external K+-concentration which suggested that the resting membrane potential of the plasmalemma is largely a K+-diffusion potential. After permeabilization of the tonoplast with nystatin the potential of the intact membrane barrier dropped from about slightly negative or positive (-5.1 to +18 mV, n = 13) to negative values (-15 up to -68 mV; n = 8). This indicated that the cytoplasm of V. ventricosa was apparently negatively charged relative to the external medium. Permeabilization of the plasmalemma by addition of external nystatin resulted generally in an increase in the potential to slightly more positive values (-0.8 to +4.3 mV; n = 5), indicating that the vacuole is positively charged relative to the cytoplasm. These findings apparently end the long-term debate about the electrical properties of V. ventricosa. The results presented here support the findings of Davis (Plant Physiol. 67: 825-831, 1981), but are contrary to the results of Lainson and Field (J. Membrane Biol. 29: 81-94, 1976).

Action Potentials↗
PubMed1999

Distinct thyroid hormone-dependent expression of TrKB and p75NGFR in nonneuronal cells during the critical TH-dependent period of the cochlea.

Analyzing the thyroid hormone (TH)-dependent period of the inner ear, we observed that the presence of triiodothyronine (T3) between postnatal day 3 (P3) and P12 is sufficient for functional maturation of the auditory system. Within this short time period, an unusual transient TH-dependent expression of nonneuronal neurotrophin receptors (NT-R) trkB and p75(NGFR) was observed in correlation with neuronal and morphogenetic processes. The availability of thyroid hormone was revealed to be invariably correlated with (a) a transient expression of full-length trkB in TRalpha1-, TRalpha2- and TRbeta1-expressing hair cells concomitant to the segregation of afferent fibers and the synaptogenesis of efferent fibers; and (b) a transient expression of p75(NGFR) in TRalpha1- and TRbeta1-expressing great epithelia ridge cells in direct spatiotemporal correlation with the appearance of apoptotic cells and morphogenetic maturation of the organ. For the first time, these data suggest a TH dependency of the expression of neurotrophin receptors in nonneuronal cells. A potential role of these peculiar neurotrophin receptor expression for the conversion of the biological function of TH on innervation patterning and morphogenesis during the critical TH-dependent period of the inner ear may be considered.

Animals↗
PubMed1999

Dielectric properties of alginate beads and bound water relaxation studied by electrorotation.

The electrical and dielectric properties of Ba2+ and Ca2+ cross-linked alginate hydrogel beads were studied by means of single-particle electrorotation. The use of microstructured electrodes allowed the measurements to be performed over a wide range of medium conductivity from about 5 mS/m to 1 S/m. Within a conductivity range, the beads exhibited measurable electrorotation response at frequencies above 0.2 MHz with two well-resolved co- and antifield peaks. With increasing medium conductivity, both peaks shifted toward higher frequency and their magnitudes decreased greatly. The results were analyzed using various dielectric models that consider the beads as homogeneous spheres with conductive loss and allow the complex rotational behavior of beads to be explained in terms of conductivity and permittivity of the hydrogel. The rotation spectra could be fitted very accurately by assuming (a) a linear relationship between the internal hydrogel conductivity and the medium conductivity, and (b) a broad internal dispersion of the hydrogel centered between 20 and 40 MHz. We attribute this dispersion to the relaxation of water bound to the polysaccharide matrix of the beads. The dielectric characterization of alginate hydrogels is of enormous interest for biotechnology and medicine, where alginate beads are widely used for immobilization of cells and enzymes, for drug delivery, and as microcarriers for cell cultivation.

Alginates↗
PubMed1999

19F-MRI in vivo determination of the partial oxygen pressure in perfluorocarbon-loaded alginate capsules implanted into the peritoneal cavity and different tissues.

Semipermeable hydrogels formed with a biocompatible alginate solution and Ba(2+) ions protect encapsulated cells and tissues from a foreign immune system. For the viability and metabolic activity of the encapsulated materials, a sufficient oxygen supply inside the capsules is necessary. Quantitative (19)F-MRI was performed on perfluorocarbon-loaded alginate capsules implanted into the peritoneal cavity, the musculus quadriceps femoris, and beneath the kidney capsule of rats, in order to determine in vivo the partial oxygen pressure (pO(2)) inside the capsules at these implantation sites. The temporal behavior of the pO(2) values was observed for at least 3 months. The most stable values over time were observed in the kidney, where inter-rat pO(2) differences were considerable. In the muscle, the values were very high directly after implantation and decreased to nearly zero after 2 weeks. In the peritoneal cavity, values changed randomly over a wide range between different rats and over time. Magn Reson Med 42:1039-1047, 1999.

Alginates↗
PubMed1999

Fast NMR flow measurements in plants using FLASH imaging.

A fast method for quantitative NMR imaging of flow velocities in intact plants is described. The purpose of this method is to observe dynamic changes of flow velocity in the xylem of plants after fast changes of environmental conditions. The spatial image resolution is 47 x 188 micrometer(2) in-plane. The method applies a fast gradient echo sequence (FLASH). Compared to other flow NMR imaging sequences, the imaging time was reduced by a factor of 6 with comparable signal-to-noise ratio. A complete flow measurement consists of a set of 8 different flow weighted images with a total acquisition time of 3.5 min.

Magnetic Resonance Spectroscopy↗
PubMed1999

Fluorescence quenching of polycyclic aromatic compounds by humic substances. Part 1. Methodology for the determination of sorption coefficients.

An introduction to the methodology of fluorescence quenching measurements as an experimental tool for investigating the sorption of hydrophobic organic substances by dissolved organic matter (OM) is given. Special attention is paid to the implications of inner-filter effects (IFEs) on the determination of sorption coefficients. The essential aspects of the theoretical description of IFEs are outlined and various procedures for the IFE correction of fluorescence quenching measurements in the presence of dissolved OM are presented. Geometric parameters relevant for the quantitative description of IFE applying a 90 degrees arrangement between fluorescence excitation and detection are determined by different methods, newly developed or adapted from the literature, for the fluorescence spectrometer used in this work. Moreover, an experimental validation of the applicability of different IFE correction procedures is performed. In order to evaluate the variations of sorption coefficients that result from the use of different IFE correction procedures, the quenching of the fluorescence of the well-known polycyclic aromatic compound pyrene by a commercially available humic substance in aqueous solution is investigated. Compared to the apparent sorption coefficient, which is obtained without any IFE correction, the sorption coefficients determined with the correction of primary IFE or with the correction of primary and secondary IFE are on average ca. 40 or 60% lower. The application of different IFE correction procedures allows the determination of sorption coefficients with appropriate precision of +/- 15%.

Adsorption↗
PubMed1999

Cushing's syndrome due to an ectopic ACTH-secreting pituitary tumour mimicking occult paraneoplastic ectopic ACTH production.

A 32-year-old man presenting with typical features of Cushing's syndrome showed baseline cortisol and ACTH values indicating ACTH-dependent disease. Dynamic function tests (dexamethasone, corticotropin releasing hormone (CRH), desmopressin), were suggestive of paraneoplastic ectopic ACTH production. However, inferior petrosal sinus (IPS) ACTH sampling demonstrated a maximum baseline central (363 pmol/l)-peripheral (19 pmol/l) ACTH gradient of 19.1 for the right IPS, conventionally suggestive of Cushing's disease. However, again, IPS ACTH level did not increase after CRH stimulation. Magnetic resonance imaging, while showing no evidence of an intrasellar tumour, revealed an 1.5 x 1.0 cm mass in the left sphenoid sinus which was initially interpreted as most probably being a mucosal polyp. After neurosurgical removal of the tumour, transient secondary adrenal insufficiency was present. The structure and immunostaining characteristics of the tumour demonstrated an ACTH cell adenoma of the pituitary. Ectopic ACTH-secreting pituitary adenomas may cause significant difficulties in differential diagnosis, localisation and appropriate therapy. Thus, although these tumours are rare, they should be included in the list of possible causes of ACTH-dependent Cushing's syndrome.

ACTH Syndrome, Ectopic↗
PubMed1999

Renal involvement in Gambian children with cerebral or mild malaria.

Kidney function was studied in 80 Gambian children with cerebral malaria, 73 children with mild malaria, and in 19 children with other febrile illnesses. Serum creatinine was measured, and the excretion in urine of immunoglobulin G, transferrin, albumin and alpha 1 microglobulin was determined. Twenty-five percent of children with cerebral malaria, and 4% of children with mild malaria had an elevated serum creatinine above 62 mumol/l. Increased urinary protein excretion was frequent: 53% of children with cerebral malaria had a glomerulo-tubular pattern of protein excretion, and 46% a tubular pattern. Median albuminuria was 68 mg/l in children with cerebral malaria, 18 mg/l in children with mild malaria, and 9 mg/l in febrile children with other diseases (P < 0.0001). There was no significant association between the proteinuria and height of fever or the degree of parasitaemia, and there was no significant association between death and signs of renal impairment. Renal involvement is common in children with malaria in The Gambia, with prerenal, glomerular, and tubulo-interstitial factors contributing. It is more pronounced in children with cerebral malaria than in those with mild malaria. However, renal dysfunction is relatively mild and does not indicate a worse prognosis.

Alpha-Globulins↗
PubMed1999

Maxadilan interacts with receptors for pituitary adenylyl cyclase activating peptide in human SH-SY5Y and SK-N-MC neuroblastoma cells.

Receptors for pituitary adenylyl cyclase activating peptide (PACAP) have been identified in human SH-SY5Y neuroblastoma cells with PACAP being 1000-fold more potent than vasoactive intestinal peptide (VIP) in [(125)I]PACAP binding inhibition and stimulation of cAMP accumulation. Maxadilan, a vasodilator peptide from the salivary gland of the sand fly Lutzomyia longipalpis also specifically bound to SH-SY5Y cells, and was equipotent to PACAP in [(125)I]PACAP and [(125)I]maxadilan binding inhibition, and stimulation of cAMP accumulation. Maxadilan and PACAP also increased the cytosolic free calcium concentration. In human SK-N-MC neuroblastoma cells PACAP, VIP and maxadilan equipotently stimulated cAMP accumulation. The maximal effects of VIP and maxadilan were additive and reached those of PACAP alone. In human T47D breast carcinoma cells PACAP and VIP were also equipotent in the stimulation of cAMP accumulation, but maxadilan was inactive. The results are consistent with the interaction of maxadilan with PACAP specific PAC(1)receptors in SH-SY5Y cells, but not with VPAC receptors, not differentiating between VIP and PACAP in T47D cells. Moreover, maxadilan is a PAC(1)receptor specific agonist which allows discrimination of co-expressed PAC(1)and VPAC receptors in SK-N-MC cells.

Binding, Competitive↗
PubMed1999

Allosteric properties of cyanobacterial cytochrome c oxidase: inhibition of the coupled enzyme by ATP and stimulation by ADP.

Thorough analysis of the cta operon of Synechocystis sp. PCC6803 (grown in high-concentration salt medium to enhance the expression of respiratory proteins) showed that, apart from ctaCDE and Fb genes potentially encoding subunits I, II, III, and a small pseudo-bacteria-like subunit-IV of unknown function, a large mitochondria-like cta-Fm gene and a pronounced terminator structure are additional components of the operon. The deduced cta Fm gene product shows approximately 50% and 20% sequence identity to the Saccharomyces cerevisiae and beef heart mitochondrial COIV proteins, respectively. It also shows amino acid regions (near the N terminus, on the cytosolic side) with conspicuous sequence similarities to adenylate-binding proteins such as ATP synthase beta subunit Walker A and B consensus regions or to adenylate kinase. We suggest that, similar to the situation with beef heart mitochondria, it is the mitochondria-like subunit-IV of the cyanobacterial aa3-type cytochrome-c oxidase that confers allosteric properties to the cyanobacterial enzyme, the H+/e- ratios of cytochrome c oxidation being significantly lowered by ATP (intravesicular or intraliposomal) but enhanced by ADP. Therefore, the antagonistic action of ATP and ADP was in a way that the redox reaction proper, was always significantly less affected than the coupled proton translocation. Evolutionary and ecological implications of the unusual allosteric regulation of a prokaryotic cytochrome-c oxidase is discussed.

Adenosine Diphosphate↗
PubMed1999

[Quality of life following transplantation. The impact ofa new immunosuppressive substance].

The improvement of quality of life is one of the major goals in the treatment of patients after renal transplantation. While immunosuppressive therapy is present in almost all of these patients, little is known about the effects of newer immunosuppressive agents. We therefore investigated the impact of tacrolimus on life quality. From November 1997 to January 1998, a questionnaire was handed out which focussed on physical and mental problems as well as sexual capacity and the attitudes towards graft, donor and transplant related side effects. 50 kidney graft recipients treated with tacrolimus were matched to 50 patients with a cyclosporine-based immunosuppression (= controls). Values are given as mean +/- standard deviation. Tacrolimus treated patients had a mean creatinine of 1.8 +/- 0.8 mg/dl, as compared to 1.6 +/- 0.7 mg/dl in controls. The overall status of health was assessed to be good in 82% of the tacrolimus group (controls: 80%). 38% were working full-time (controls: 20%). Only 14% of patients described their physical condition as poor (16% in controls). Sexual function was good in 66% (controls: 74%) and poor in 10% (controls: 12%). Mental function was assessed to be good in 92% (controls: 82%). The majority of patients felt comfortable with their physical, sexual and mental capabilities. This was independent from the immunosuppressive regimen.

Cyclosporine↗
PubMed1998

The effect of electrical deformation forces on the electropermeabilization of erythrocyte membranes in low- and high-conductivity media.

Electrical breakdown of erythrocytes induces hemoglobin release which increases markedly with decreasing conductivity of the pulse medium. This effect presumably results from the transient, conductivity-dependent deformation forces (elongation or compression) on the cell caused by Maxwell stress. The deformation force is exerted on the plasma membrane of the cell, which can be viewed as a transient dipole induced by an applied DC electric field pulse. The induced dipole arises from the free charges that accumulate at the cell interfaces via the Maxwell-Wagner polarization mechanism. The polarization response of erythrocytes to a DC field pulse was estimated from the experimental data obtained by using two complementary frequency-domain techniques. The response is very rapid, due to the highly conductive cytosol. Measurements of the electrorotation and electrodeformation spectra over a wide conductivity range yielded the information and data required for the calculation of the deformation force as a function of frequency and external conductivity and for the calculation of the transient development of the deformation forces during the application of a DC-field pulse. These calculations showed that (i) electric force precedes and accompanies membrane charging (up to the breakdown voltage) and (ii) that under low-conductivity conditions, the electric stretching force contributes significantly to the enlargement of "electroleaks" in the plasma membrane generated by electric breakdown.

Cell Membrane Permeability↗