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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 1029 (1990), S. 185-187 
    ISSN: 0005-2736
    Keywords: (Frog skin) ; Apical membrane ; Basolateral membrane ; Conductance ; Isoproterenol ; Microelectrode
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 1069 (1991), S. 87-93 
    ISSN: 0005-2736
    Keywords: Circuit analysis ; Cultured renal cell line (A6) ; Membrane conductance ; Microelectrode ; Specific membrane conductance ; Voltage dependence
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 1110 (1992), S. 239-242 
    ISSN: 0005-2736
    Keywords: A6 cell ; Basolateral potassium ion conductance ; Hyposmotic challenge ; Microelectrode ; Potassium ion conductance
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 1066 (1991), S. 111-114 
    ISSN: 0005-2736
    Keywords: (Necturus kidney) ; Basolateral membrane potential ; Hyperpolarization ; Membrane potential ; Organic acid ; Proximal tubule ; Sodium-potassium ion exchange ; pH effect
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Comparative Biochemistry and Physiology -- Part A: Physiology 90 (1988), S. 835 
    ISSN: 0300-9629
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Comparative Biochemistry and Physiology -- Part A: Physiology 90 (1988), S. 826 
    ISSN: 0300-9629
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 412 (1988), S. 369-375 
    ISSN: 1432-2013
    Keywords: Renal proximal tubule ; Necturus ; Peritubular membrane potential ; Transepithelial membrane potential ; Potassium apparent transference number ; Alkalinization ; Barium ; Bicarbonate free
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Short-term peritubular alkalinization from 7.5 to 8.5 hyperpolarized (−8.8 mV) the basolateral membrane potential (V 1) in HCO 3 − free Hepes buffered Necturus renal proximal tubule cells. This sustained base induced hyperpolarization (BIH) was associated with an increase in the peritubular apparent transference number for potassium ( $$t_{K^ + } $$ ). The apparent transference number for potassium ( $$t_{K^ + } $$ ) was estimated at pH 7.5 and 8.5 by raising peritubular K+ from 2.5 to 10 mmol/l. $$t_{K^ + } $$ increased linearly asV 1 hyperpolarized, whereas $$t_{K^ + } $$ measured in the presence of peritubular Ba2+ at pH 7.5 and 8.5 was nearly zero. However, the BIH persisted in the presence of barium at the peritubular, luminal or both sides of the epithelium. Moreover this BIH was also accompanied by a small hyperpolarization (−0.4 mV) of the transepithelial membrane potential (V 3) in the absence or presence of peritubular and/or luminal Ba2+. Therefore we conclude that BIH must originate from additional mechanisms other than an increase in peritubular or luminal potassium conductance.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 417 (1991), S. 463-468 
    ISSN: 1432-2013
    Keywords: Renal tight cultured cell line (A6) ; Specific membrane conductances ; Barium ; Microelectrodes ; Circuit analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Confluent monolayers of the cultured renal distal tubule cell line (A6) were impaled with microelectrodes under short-circuit conditions. Specific membrane conductances were calculated from equivalent circuit equations. Transport properties of the apical and basolateral membranes were investigated during control conditions and short-term increases in basolateral potassium concentration [K+] from 2.5 to 20 mmol/l, with or without 0.5 mmol/l Ba2+ at the basolateral side. As in most other epithelia, the apical membrane represents the major resistive barrier. Transcellular, apical and basolateral membrane conductances (g c, g o and g i respectively), obtained from 22 acceptable microelectrode studies, averaged 61, 80 and 292 μS/cm2, respectively. There was a highly significant correlation between short-circuit current (I sc) and g o, whereas g i was unrelated to I sc. The I sc, which averaged 4.1 μA/cm2, was almost completely blocked by amiloride. This was associated with fast hyperpolarization; the intracellular potential (V sc) increased from −69 to −83 mV and the fractional apical resistance rose to nearly 100%. Using the values of V sc during amiloride at normal and high [K+], an apparent transference number for K+ at the basolateral membrane of 0.72 can be calculated. This value corresponds with the decrease in g i to about 25% of the control values after blocking the K+ channels with Ba2+. The nature of the remaining conductance is presently unclear. The cellular current decreased during high [K+] and Ba2+, in part resulting from reduction of the electrochemical gradient for apical Na+ uptake due to the depolarization. In addition, g o decreased to less than 40%, which is considerably lower than predicted by the constant-field equation; this might indicate voltage sensitivity of the apical Na+ permeability.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 420 (1992), S. 559-565 
    ISSN: 1432-2013
    Keywords: Microelectrodes ; Equivalent circuit analysis ; Dexamethasone ; Chloride channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Conductance of apical and basolateral membranes in short-circuited cultured renal distal cells (A6) was determined using microelectrodes. Epithelia were pre-incubated with 0.1 μmol/l dexamethasone in the presence of 4 μmol/l amiloride to prevent increase in apical Na+ entry. Omission of amiloride increased the I SC from 5.7 to 27.6 μA/cm2 due to the rise in apical membrane conductance from 21 to 595 μS/cm2. Apical fractional resistance decreased from 0.89 to 0.40 and cells depolarized from −52 to −4 mV. Basolateral membrane conductance, which was 320 μS/cm2 at partially inhibited transport, was not significantly altered during the first 2 min following establishment of high transport activity; it started to increase thereafter reaching a more than threefold higher value of 1324 μS/cm2 within 12 min. The gain cannot be explained by increase in partial K+ conductance. Disappearance of the conductance after reduction of basolateral Cl− or in the presence of the Cl− channel blocker 5-nitro-2-(3-phenylpropylamino)benzoate indicates a Cl− conductance, which appears to be activated by depolarization.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 422 (1993), S. 546-551 
    ISSN: 1432-2013
    Keywords: Microelectrodes ; Basolateral K+ conductance ; K+ currents ; Homocellular regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Homocellular regulation of K+ at increased transcellular Na+ transport implies an increase in K+ exit to match the intracellular K+ load. Increased K+ conductance, gK, was suggested to account for this gain. We tested whether such a mechanism is operational in A6 monolayers. Na+ transport was increased from 5.1±1.0 μA/cm2 to 20.7±1.3 μA/cm2 by preincubation with 0.1 μmol/l dexamethasone for 24 h. Basolateral K+ conductances were derived from transference numbers of K+, t K, and basolateral membrane conductances, gb, using conventional microelectrodes and circuit analysis with application of amiloride. Activation of Na+ transport induced an increase in gb from 0.333±0.067 mS/ cm2 to 1.160±0.196 mS/cm2 and t K was reduced to 0.22±0.01 from a value of 0.70±0.05 in untreated control tissues. As a result, gK remained virtually unchanged at increased Na+ transport rates. The increase in gb after dexamethasone was due to activation of a conductive leak pathway presumably for Cl−. Increased K+ efflux, I K, was a consequence of the larger driving force for K+ exit due to depolarization at an elevated Na+ transport rate. The relationship between calculated K+ fluxes and Na+ transport rate, measured as the I sc, is described by the linear function I K=0.624×I Na−0.079, which conforms with a stoichiometry 2∶3 for the fluxes of K+ and Na+ in the Na+/K+-ATPase pathway. Our data show that homocellular regulation of K+ in A6 cells is not due to up-regulation of g K .
    Type of Medium: Electronic Resource
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