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  • 1
    Digitale Medien
    Digitale Medien
    A constitutively open potassium channel formed by KCNQ1 and KCNE3 (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 403 (2000), S. 196-199 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] Mutations in all four known KCNQ potassium channel α-subunit genes lead to human diseases. KCNQ1 (KvLQT1) interacts with the β-subunit KCNE1 (IsK, minK) to form the slow, depolarization-activated potassium current IKs that is affected in some forms of cardiac ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/35003200
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    pH regulation in isolated in vitro perfused rat colonic crypts (2000)
    Springer
    Pflügers Archiv 441 (2000), S. 118-124 
    Details
    ISSN: 1432-2013
    Schlagwort(e): BCECF fluorescence Luminal permeability Na+-dependent HCO3–/Cl– exchanger Na+/H+ exchange Short-chain fatty acids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. We investigated disorders and regulation of cytosolic pH (pHi) in isolated perfused crypts from rat distal colon using the pH-sensitive dye BCECF. This preparation allows distinct examination of either luminal or basolateral transport. The effects of luminal weak organic acids and bases on pHi were examined. The physiological concentrations of both luminal CO2/HCO3 – and acetic acid/acetate acidified pHi significantly, but less than when applied from the basolateral side. Corresponding changes (luminal versus basolateral) in pHi were –0.17±0.04 versus –0.39±0.04, (n=8) and –0.15±0.02 versus –0.41±0.04, (n=8), respectively. Basolateral versus luminal application of NH3/NH4 + led to a more marked change in pHi, namely 0.35±0.03 versus 0.008±0.007 pH units, (n=19). The luminal perfusion of NH3/NH4 + was controlled by applying fura-2 acid to the luminal side and at the same time recording fura-2-specific fluorescence. Hence, the influence of luminal acid/base on colonic pHi homeostasis was limited. To examine pHi regulation, we investigated the recovery from an intracellular acid load using the NH3/NH4 + pulse method. Recovery was completely dependent on basolateral Na+, indicating that luminal acid/base transport does not play a major role in pHi homeostasis. The basolateral transporters involved in pHi recovery are probably the EIPA- and HOE694-inhibitable (IC50=0.2 and 2 µmol/l, respectively) Na+/H+ exchanger NHE1 and the DIDS-inhibitable Na+-dependent HCO3 – importer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004240000377
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Inwardly rectifying K+ channels in the basolateral membrane of rat pancreatic acini (2000)
    Springer
    Pflügers Archiv 441 (2000), S. 331-340 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Electrolyte secretion Inwardly rectifying K+ channels (Kir) K+ recycling Rat pancreatic acini
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. Previous studies of the whole-cell K+ conductance suggest the presence of inwardly rectifying K+ channels (Kir) in rat pancreatic acini (RPAs). Here we investigate the properties of Kir of RPAs using patch-clamp techniques. The whole-cell current-to-voltage relationship of freshly isolated RPAs was steeper for inward currents than for outward currents when the extracellular K+ concentration ([K+]o) was raised. With a high [K+]o (145 mM), external application of Ba2+ and Cs+ blocked the inward K+ current in a voltage-dependent manner. The apparent IC50 of Ba2+ was 8.5±1.9 µM and 1.1±0.2 µM at –70 mV and –130 mV, respectively (n=5). The IC50 of Cs+ was 3.5±1.1 mM and 0.2±0.1 mM at –60 mV and –120 mV, respectively (n=4). Application of Ba2+ (0.1 mM) to the extracellular solution reversibly depolarized RPAs from –43±1.1 mV to –37±1.2 mV (n=20). In the cell-attached configuration with 145 mM KCl in the pipette solution, we observed inwardly rectifying channels with a high open probability (P o) of 0.85±0.02 (n=6) and a slope conductance (G s) of 30±2.8 pS (n=13). The same type of channel was observed in the outside-out patch. We could also observe a very small conductance K+ channel which was resistant to 0.1 mM Ba2+ and did not show inward rectification (n=11). RT-PCR analysis of RPA confirmed the presence of transcripts for Kir2.1, Kir2.3 and Kir7.1 subfamilies as molecular candidates for the observed channels. The above results demonstrate the presence of Kir channels in the basolateral membrane of the RPA, which may be important for the K+ recycling process during electrolyte secretion as well as for maintaining a hyperpolarized membrane.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004240000427
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    KCNE1 reverses the response of the human K+ channel KCNQ1 to cytosolic pH changes and alters its pharmacology and sensitivity to temperature (2000)
    Springer
    Pflügers Archiv 441 (2000), S. 368-378 
    Details
    ISSN: 1432-2013
    Schlagwort(e): KvLQT1 minK Temperature Clotrimazole Tetrapentylammonium Mefenamic acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. Previous studies have shown that heteromultimeric KCNQ1/KCNE1 (KvLQT1/minK) channels and homomultimeric KCNQ1 (KvLQT1) channels exhibit different current properties, e.g. distinct kinetics and different sensitivities to drugs. In this study we report on the divergent responses to internal pH changes and further characterize some of the current properties of the human isoforms of KCNQ1 and KCNE1 expressed in Chinese hamster ovary (CHO) cells or Xenopus laevis oocytes. Decreasing the bath temperature from 37 °C to 20 °C increased the half-activation time by a factor of 5 for KCNQ1/KCNE1 currents (I Ks) but by only twofold (not significant) for KCNQ1 currents (I K) in CHO cells. Acidification of cytosolic pH (pHi) increased I Ks but decreased I K whereas intracellular alkalinization decreased I Ks but increased I K. pHi-induced changes in intracellular Ca2+ activity ([Ca2+]i) did not correlate with the current responses. At 20 °C mefenamic acid (0.1 mM) significantly augmented I Ks but slightly decreased I K. It changed the slow activation kinetics of I Ks to an instantaneous onset. The form of the current/voltage (I/V) curve changed from sigmoidal to almost linear. In contrast, at 37 °C, mefenamic acid also increased I Ks but slowed the activation kinetics and shifted the voltage activation to more hyperpolarized values without markedly affecting the sigmoidal shape of the I/V curve. The potassium channel blockers clotrimazole and tetrapentylammonium (TPeA) inhibited I Ks with a lower potency than I K. These results show that coexpression of KCNE1 reversed pH regulation of KCNQ1 from inhibition to activation by acidic pHi. In addition, KCNE1 altered the pharmacological properties and sensitivity to temperature of KCNQ1. The pH-dependence of I Ks might be of clinical and pathophysiological relevance in the pathogenesis of ischaemic cardiac arrhythmias.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004240000434
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    The very small-conductance K+ channel KVLQT1 and epithelial function (2000)
    Springer
    Pflügers Archiv 440 (2000), S. 202-206 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Cl– secretory epithelia Epithelial tissue KVLQT1 Very small conductance K+ channel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. KVLQT1 (KCNQ1) is a very small conductance K+ channel distributed widely in epithelial and non-epithelial tissues. Its specific biophysical and pharmacological properties are determined by the regulatory subunits IsK (KCNE1) and MiRP2 (KCNE3). In epithelial cells of the inner ear, pancreas, and airways it interacts with IsK to conduct a voltage-gated and slowly activating K+ current. In the colon it coassembles with KCNE3 to conduct an instantaneous and constitutively active K+ current. In Cl– secretory epithelia, such as the colon and pancreas, this K+ channel provides the driving force for Cl– exit and is located in the basolateral membrane. In the inner ear it enables luminal secretion of K+ into the endolymphatic space. The functional relevance of KVLQT1 to epithelial function is revealed by blocking it pharmacologically or by studying animals with a genetic defect for it, which result in the breakdown of colonic Cl– secretion and endolymph production, respectively. KVLQT1 K+ channels are activated via cAMP or Ca2+ and inhibited by the chromanol 293B. Interaction with as yet unknown regulatory subunits may determine the properties of KVLQT1 in the rectal gland and other epithelial tissues in which KVLQT1 is not inhibited by chromanols.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004240000257
    Standort Signatur Einschränkungen Verfügbarkeit
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