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  • 1
    Digitale Medien
    Digitale Medien
    HMR 1098: An Inhibitor of Cardiac ATP-Sensitive Potassium Channels (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Cardiovascular drug reviews 18 (2000), S. 0 
    Details
    ISSN: 1527-3466
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1527-3466.2000.tb00040.x
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Transport characteristics of a murine renal Na/Pi (1995)
    Springer
    Pflügers Archiv 430 (1995), S. 830-836 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Renal proximal tubule ; Na/Pi-cotransport ; Xenopus laevis oocytes ; Electrogenicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract A complementary deoxyribonucleic acid (cDNA) corresponding to a murine renal cortical Na/phosphate-(Na/Pi-) cotransporter was isolated and its transport properties characterized by electrophysiological techniques after expression in Xenopus laevis oocytes. A Na-dependent inward movement of positive charges (“short-circuit current”) was observed upon superfusion with Pi (and with arsenate). Increasing the Na concentration led to a sigmoidal elevation in Pi-induced short-circuit current; the apparent Michaelis constant, K m, (around 40 mM Na) was increased by lowering the pH of the superfusate but was not influenced by altering the Pi concentration. Increasing the Pi (and arsenate) concentration led to a hyperbolic elevation in Na-dependent short-circuit current (apparent Km for Pi at 100 mM Na was around 0.1 mM; apparent Km for arsenate was around 1 mM); lowering the Na concentration decreased the apparent affinity for Pi. The Pi-induced short-circuit current was lower at more acidic pH values (at pH 6.3 it was about 50% of the value at pH 7.8); this pH dependence was similar if the Pi concentration was calculated in total, or if distinction was made between its mono- and divalent forms. Thus, the pH dependence of Na-dependent Pi transport (total Pi) may not be related primarily to a pH-dependent alteration in the availability of divalent Pi, but includes also a competitive interaction of Na with protons. The effect of Pi and Na concentration on the apparent Km values for Na or Pi, respectively, provides evidence for an ordered interaction of “cosubstrate” (Na first) and “substrate” (Pi or arsenate second).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00386183
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Inhibitory effects of oxidants on n-type K+ channels in T lymphocytes and Xenopus oocytes (1997)
    Springer
    Pflügers Archiv 433 (1997), S. 626-632 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Key words T lymphocytes ; Xenopus oocytes ; Voltage-gated potassium currents ; Oxidative agents ; Apoptosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Reactive oxygen species (ROS) appear to be involved in Fas-induced programmed cell death. We have previously demonstrated a tyrosine-kinase-dependent inhibition of the n-type K+ channels (Kn) by Fas stimulation. Thus, the effect of hydrogen peroxide (H2O2) on the function of Kn was examined using the patch-clamp technique. Incubation of Jurkat human T lymphocytes with 100 μM H2O2 resulted in a 46 ± 5% inhibition of the macroscopic whole-cell current. Experiments performed at the single-channel level using the cell-attached configuration revealed that the probability of the channel being open diminished upon incubation in H2O2. The effect was not dependent on src-like kinases, since H2O2 did not trigger tyrosine phosphorylation of the Kn channel protein and herbimycin A did not prevent channel inhibition. Kv1.3 channels underly the Kn of T lymphocytes and were expressed in Xenopus oocytes and subjected to electrophysiological analysis by the two-electrode voltage-clamp technique. Application of 1 mM H2O2 and 500 μM t-BOOH (tert, butylhydroperoxide) resulted in a marked inhibition of the K+ current within 20 min. Both the membrane-permeable thiol-group oxidizing agent DTNP [2,2′-dithiobis-(5-nitropyridine)] and the membrane-impermeable DTNB [5,5′-Dithiobis-(2-nitrobenzoic acid)] (50 μM) inhibited Kv1.3 channels, suggesting that extracellular domains of Kv1.3 are affected. These results point to a direct modulation of Kn by various oxidative agents.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004240050323
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Molecular and functional characterization of s-KCNQ1 potassium channel from rectal gland of Squalus acanthias (1999)
    Springer
    Pflügers Archiv 437 (1999), S. 298-304 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Key words Chloride secretion ; Electrophysiology ; IsK(minK) ; Rapid amplification of cDNA ends/polymerase chain reaction (RACE/PCR) ; Xenopus oocytes ; 293B
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Functional and pharmacological data point to the involvement of KCNQ1/IsK potassium channels in the basolateral potassium conductance of secretory epithelia. In this study, we report the cloning and electrophysiological characterization of the KCNQ1 protein from the salt secretory rectal gland of the spiny dogfish (Squalus acanthias). The S. acanthias KCNQ1 (s-KCNQ1) cDNA was cloned by polymerase chain reaction (PCR) intensive techniques and showed overall sequence similarities with the KCNQ1 potassium channel subunits of Man, mouse and Xenopus laevis of 64, 70 and 77%, respectively, at the translated amino acid level. Analysis of s-KCNQ1 expression on a Northern blot containing RNA from heart, rectal gland, kidney, brain, intestine, testis, liver and gills revealed distinct expression of 7.4-kb s-KCNQ1 transcripts only in rectal gland and heart. Voltage-clamp analysis of s-KCNQ1 expressed in Xenopus oocytes showed pronounced electrophysiological similarities to human and murine KCNQ1 isoforms, with a comparable sensitivity to inhibition by the chromanol 293B. Coexpression of s-KCNQ1 with human-IsK (h-IsK) induced currents with faster activation kinetics and stronger rectification than observed after coexpression of human KCNQ1 with h-IsK, with the voltage threshold of activation shifted to more negative potentials. The low activation threshold at approximately –60 mV in combination with the high expression in rectal gland cells make s-KCNQ1 a potential candidate responsible for the basolateral potassium conductance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004240050783
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Protein kinase C consensus sites and the regulation of renal Na/Pi-cotransport (NaPi-2) expressed in XENOPUS laevis oocytes (1995)
    Springer
    Pflügers Archiv 430 (1995), S. 819-824 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Na/Pi cotransport ; Parathyroid hormone ; Protein phosphorylation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Renal brush border membrane sodium/phosphate (Na/Pi)-cotransport activity is inhibited by hormonal mechanisms involving activation of protein kinases A and C. The recently cloned rat renal Na/Pi cotransporter (NaPi-2) contains several protein kinase C but no protein kinase A consensus sites [17, 20]. In the present study we have expressed wild type and polymutant (protein kinase C consensus sites removed) NaPi-2-transporters in Xenopus laevis oocytes. The expression of transport function as well as the basic transport properties were unaffected by the removal of the consensus sites. Pharmacological activation of protein kinase C with phorbol 12,13-didecanoate (PDD) led to a time-dependent inhibition of expressed wild type Na/Picotransport function; simultaneous exposure to staurosporine (0.3) prevented the PDD induced (50 nM) inhibition. The kinase-C-mediated inhibition was not prevented by the removal of the protein kinase C consensus sites. Pharmacological activation of protein kinase A (dibutyryl adenosine 3′:5′:cyclic monophosphate (cAMP)/forskolin) had no effect on wild type NaPi-2-induced oocyte Na/Pi cotransport. It is concluded that the protein-kinase-C-mediated regulation of expressed Na/Pi-cotransport does not involve the predicted consensus sites. The involvement of “cryptic” phosphorylation sites and/or of a phosphorylated “regulatory” protein is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00386181
    Standort Signatur Einschränkungen Verfügbarkeit
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