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  • Springer  (74)
  • 1995-1999  (74)
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  • 1
    Electronic Resource
    Electronic Resource
    Photofrin II Sensitized Modifications of Ion Transport Across the Plasma Membrane of an Epithelial Cell Line: I. Electrical Measurements at the Whole-Cell Level (1998)
    Springer
    The journal of membrane biology 166 (1998), S. 179-185 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Photosensitization — Photofrin II — Patch-clamp — OK-cells — Membrane potential — Membrane conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Photofrin II is a photosensitizer frequently applied in photodynamic therapy. Light-induced tumor cell inactivation observed in the presence of this substance has been suggested to start with modifications at the level of cellular membranes. In the present study electrophysiological techniques are applied in order to investigate the action of photofrin II on functional properties of the plasma membrane of opossum kidney (OK) cells (as an epithelial model system) and of fibroblasts. Illumination of the cells in the presence of photofrin II (or Zn-phthalocyanine) leads to comparatively fast depolarization of the membrane potential. It is caused by a strong change of the membrane conductance which proceeds in two phases. Both phases contribute to a loss of ion selectivity of the plasma membrane between K+ and Na+. In the first phase, specific pathways for K+, which determine the resting potential under physiological conditions, are inactivated. The second phase is distinguished by a marked increase of a nonselective conductance. The increase of the latter — after light-induced initiation — continues in the dark. The conclusions are derived from light-induced, time-dependent changes of the membrane conductance and of the shape of the current-voltage relationship detected under different experimental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900459
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of Free Radicals on Partial Reactions of the Na,K-ATPase (1997)
    Springer
    The journal of membrane biology 156 (1997), S. 63 -71 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Na,K–ATPase — Partial reactions — Free radicals — Ionizing radiation — Ion transport — Enzymatic activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The function of the Na,K-ATPase is known to be considerably impaired in the presence of free radicals such as OH•. While previous experiments were largely based on the loss of enzymatic activity of the protein, this is the first communication dealing with partial reactions of the pump cycle in the presence of free radicals produced by water radiolysis. Three different system states, which are directly involved in ion transfer catalyzed by the enzyme, showed similar sensitivity to free radical action. This is indicated by largely identical D37-doses of the decay of the reaction amplitudes investigated. The decrease in the efficiency of the enzyme functions was largely due to a lethal damage of pump molecules. A kinetic analysis of the ATP-induced conformational transition E1→ E2 revealed, however, that a minor component of the inactivation is due to a reduction of the transition rate constant. The decrease of the enzymatic activity could be simulated by the decay of the rate-limiting conformational transition. This finding indicates the conservation of a close coupling between ATP-hydrolysis and sodium translocation process throughout free-radical induced inactivation. As a result of the tight coupling, enzyme modification at different system states leads to similar functional consequences for the protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900188
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  • 3
    Electronic Resource
    Electronic Resource
    Modelling the control of ovulation and polycystic ovary syndrome (1997)
    Springer
    Journal of mathematical biology 36 (1997), S. 95-118 
    Details
    ISSN: 1432-1416
    Keywords: Key words: Ovulation ; Lacker models ; Polycystic ovary syndrome ; PCOS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract.  The control of ovulation in mammalian species appears to be a highly robust process. The primary mechanism is believed to be competition amongst a group of developing follicles, mediated by a hormonal feedback loop involving in the first instance the pituitary. Successful follicles reach maturity and ovulate, the remainder atrophy and die. A model of this control process has been derived by Lacker and his group. Based on simple qualitative assumptions about the hormonal feedback loop, this is able to reflect many of the basic physiological features of ovulation in mammals. However, a fundamental hypothesis of Lacker’s work is that all follicles are identical and respond to hormonal signals in precisely the same way. Not only is this improbable, but it also leads to several aspects of the model which are qualitatively unrealistic, most notable of these is its inability to accurately model the condition known as Polycystic Ovary Syndrome. This common malfunction of the ovulatory control mechanism accounts for up to three-quarters of cases of anovulatory infertility in humans and its understanding is therefore of considerable medical significance. In this paper we extend the analysis of Lacker’s model to the case of non-identical follicles; this allows us to obtain behaviour much closer to that observed in PCOS patients and to draw some tentative conclusions about the mechanisms underlying this condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002850050092
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  • 4
    Electronic Resource
    Electronic Resource
    Photofrin II Sensitized Modifications of Ion Transport Across the Plasma Membrane of an Epithelial Cell Line: II. Analysis at the Level of Membrane Patches (1998)
    Springer
    The journal of membrane biology 166 (1998), S. 187-196 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Photosensitization — Photofrin II — Patch-clamp — OK-cells — Ion channels — Leak conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. In the first part of this study, photofrin II sensitized membrane modifications of OK-cells were investigated at the level of macroscopic membrane currents. In this second part, the inside-out configuration of the patch-clamp technique is applied to analyze the phenomena at the microscopic level. It is shown that the characteristic single channel fluctuations of the electric current disappear after the start of illumination of membrane patches in the presence of photofrin II. This holds for all three types of ion channels investigated: the large-conductance Ca2+-dependent K+ channel (maxi-KCa), a K+ channel of small conductance (sK), and a stretch-activated nonselective cation channel (SA-cat). Part of the experiments show a transient activation of the channels (indicated by an increase of the probability in the open-channel state) before the channels are converted into a closed nonconductive state. Inactivation of all three channel types proceeds by a continuous reduction of their open probability, while the single channel conductance values are not affected. The process of photodynamically induced channel inactivation is followed by a pronounced increase of the leak conductance of the plasma membrane. The latter process — after light-induced initiation — is found to continue in the dark. The ionic pathways underlying the leak conductance also allow permeation of Ca2+ ions. The resulting Ca2+-flux may contribute to the photodynamically induced increase of the intracellular Ca2+ concentration observed in various cell lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900460
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  • 5
    Electronic Resource
    Electronic Resource
    Transfer of a grapevine stilbene synthase gene to rice (Oryza sativa L.) (1997)
    Springer
    Plant cell reports 16 (1997), S. 668-673 
    Details
    ISSN: 1432-203X
    Keywords: Key wordsOryza sativa ; Pyricularia oryzae ; Transformation ; Stilbene synthase ; Phytoalexin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A gene derived from grapevine (Vitis vinifera) coding for stilbene synthase has been transferred into protoplasts of the commercially important japonica rice cultivar Nipponbare using PEG-mediated direct gene transfer. Transgenic plants were regenerated from calli selected on kanamycin. Southern blot analysis of genomic DNA isolated from regenerants and progeny plants demonstrated that the stilbene synthase gene is stably integrated in the genome of transgenic rice plants and inherited in the offspring. The transient formation of stilbene-synthase-specific mRNA shortly after inoculation with the fungus of the rice blast Pyricularia oryzae has demonstrated that the grapevine stilbene synthase promoter is also active in monocotyledonous plants. Preliminary results indicate an enhanced resistance of transgenic rice to P. oryzae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002990050299
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of the activity of fatty-acid epoxide hydrolase in seeds of castor bean (Ricinus communis L.) (1995)
    Springer
    Planta 197 (1995), S. 84-88 
    Details
    ISSN: 1432-2048
    Keywords: Epoxide hydrolase ; Epoxy fatty acid ; Glyoxysome kw]Ricinus ; Seed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Epoxide hydrolase (EC 3.3.2.3) activity was measured with [1-14C]cis-9,10-epoxystearic acid as the substrate. Homogenates were prepared from the endosperm tissue of germinating seeds of castor bean (Ricinus communis L. zanzibariensis). The activity of fatty-acid epoxide hydrolase was characterized with respect to dependence on time, amount of protein, pH and temperature. Analyses of enzyme distribution in endosperm, cotyledons, root and hypocotyl showed the highest total activity in the endosperm, less in the cotyledons and low activity in the root and hypocotyl. The specific activity was similar for cotyledons and endosperm. Analysis of the temporal expression of the enzyme in the endosperm during germination revealed high activity already in the imbibed seed. Activity was maximal between days four to six and then decreased at the end of one week. Subcellular fractionation of endosperm revealed a dual distribution of activity between the glyoxysomal and the cytosolic fractions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239943
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  • 7
    Electronic Resource
    Electronic Resource
    Cloning and expression of the Vitreoscilla hemoglobin gene in pseudomonads: effects on cell growth (1995)
    Springer
    Applied microbiology and biotechnology 44 (1995), S. 419-424 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  The gene (vgb) encoding the hemoglobin (VtHb) of Vitreoscilla sp. was cloned into a broad-host-range vector and stably transformed into Pseudomonas putida, Pseudomonas aeruginosa, and Xanthomonas maltophilia. vgb was stably maintained and expressed in functional form in all three species. When growth of the P. aeruginosa and X. maltophilia transformants in Luria-Bertani medium was compared with that of each corresponding untransformed strain, the VtHb-producing strains reached slightly higher maximum viable cell numbers, had significantly increased viability after extended times in culture, and, like E. coli that produces VtHb, had significantly lower respiration rates. The VtHb-producing strain of P. putida also reached a slightly higher maximum viable cell number than its corresponding untransformed strain, but was significantly less viable after extended times in culture and, unlike the case in E. coli, had a generally higher respiration rate than the untransformed strain. When growth was monitored by absorbance, the results were similar to those obtained with viable cell counts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530050576
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  • 8
    Electronic Resource
    Electronic Resource
    Cloning and expression of the Vitreoscilla hemoglobin gene in pseudomonads: effects on cell growth (1995)
    Springer
    Applied microbiology and biotechnology 44 (1995), S. 419-424 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The gene (vgb) encoding the hemoglobin (VtHb) of Vitreoscilla sp. was cloned into a broad-host-range vector and stably transformed into Pseudomonas putida, Pseudomonas aeruginosa, and Xanthomonas maltophilia. vgb was stably maintained and expressed in functional form in all three species. When growth of the P. aeruginosa and X. maltophilia transformants in Luria-Bertani medium was compared with that of each corresponding untransformed strain, the VtHb-producing strains reached slightly higher maximum viable cell numbers, had significantly increased viability after extebded times in culture, and, like E. coli that produces VtHb, had significantly lower respiration rates. The VtHb-producing strain of P. putida also reached a slightly higher maximum viable cell number than its corresponding untransformed strain, but was significantly less viable after extended times in culture and, unlike the case in E. coli, had a generally higher respiration rate than the untransformed strain. When growth was monitored by absorbance, the results were similar to those obtained with viable cell counts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169938
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  • 9
    Electronic Resource
    Electronic Resource
    Parathyroid Hormone-Related Protein (1–37) Induces cAMP Response in Human Osteoblast-Like Cells (1998)
    Springer
    Calcified tissue international 62 (1998), S. 250-254 
    Details
    ISSN: 1432-0827
    Keywords: Key words: PTHrP – PTH — cAMP — Human osteoblast-like cells — CHO cells — UMR 106-01 cells.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. During recent years parathyroid hormone-related protein (PTHrP) research has been focused on the physiological functions of different fragments of the PTHrP molecule. Here we demonstrate that PTHrP (1–37) induced cyclic adenosine monophosphate (cAMP) response in primary human osteoblast-like cells, which were well characterized by the presence of alkaline phosphatase activity and osteocalcin production after stimulation with 1,25-dihydroxyvitamin D3. However, there was no cAMP response to PTHrP (58–77). Furthermore, the response to PTHrP (1–37) was dose dependent, with a significant increase at 1 nM. The presence of PTHrP (1–37)-induced cAMP response in human osteoblast-like cells implies that aminoterminal PTHrP fragments may exert important functions in the bone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900425
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  • 10
    Electronic Resource
    Electronic Resource
    Volvox germline-specific genes that are putative targets of RegA repression encode chloroplast proteins (1999)
    Springer
    Current genetics 36 (1999), S. 363-370 
    Details
    ISSN: 1432-0983
    Keywords: Key words Germline ; Differentiation ; RegA repression ; Volvox carteri
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Volvox carteri, regA acts as a master gene to suppress all germ cell functions in somatic cells. Its product, RegA, has features of a transcriptional repressor. Here we report cDNA sequences representing 15 nuclear genes with properties expected of RegA targets: they are expressed strongly in germ cells and in regA −, but not regA +, somatic cells. Two of them encode polypeptides with no recognizable features, but ten (like three previously sequenced ones) encode chloroplast proteins of known function, and the remaining three encode putative chloroplast proteins of unknown function. This suggests that RegA blocks reproductive development in somatic cells by preventing chloroplast biogenesis, thereby making it impossible for the cells to grow enough to reproduce.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002940050511
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