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  • basolateral membrane  (2)
  • apical membrane  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 95 (1987), S. 91-103 
    ISSN: 1432-1424
    Keywords: nystatin ; amiloride ; basolateral membrane ; toad urinary bladder ; Na+ transport ; epithelial impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Exposing the apical membrane of toad urinary bladder to the ionophore nystatin lowers its resistance to less than 100 Ω cm2. The basolateral membrane can then be studied by means of transepithelial measurements. If the mucosal solution contains more than 5mm Na+, and serosal Na+ is substituted by K+, Cs+, or N-methyl-d-glucamine, the basolateral membrane expresses what appears to be a large Na+ conductance, passing strong currents out of the cell. This pathway is insensitive to ouabain or vanadate and does not require serosal or mucosal Ca2+. In Cl-free SO 4 2− Ringer's solution it is the major conductive pathway in the basolateral membrane even though the serosal side has 60mm K+. This pathway can be blocked by serosal amiloride (K i=13.1 μm) or serosal Na+ ions (K i∼ 10 to 20mm). It also conducts Li+ and shows a voltage-dependent relaxation with characteristic rates of 10 to 20 rad sec−1 at 0 mV.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 95 (1987), S. 151-162 
    ISSN: 1432-1424
    Keywords: amiloride ; apical membrane ; Ca2+ inhibition ; epithelial transport ; membrane vesicles ; Na+ channels ; toad bladder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Direct inhibitory effects of Ca2+ and other ions on the epithelial Na+ channels were investigated by measuring the amiloride-blockable22Na+ fluxes in toad bladder vesicles containing defined amounts of mono- and divalent ions. In agreement with a previous report (H.S. Chase, Jr., and Q. Al-Awqati,J. Gen. Physiol. 81:643–666, 1983) we found that the presence of micromolar concentrations of Ca2+ in the internal (cytoplasmic) compartment of the vesicles substantially lowered the channel-mediated fluxes. This inhibition, however, was incomplete and at least 30% of the amiloride-sensitive22Na+ uptake could not be blocked by Ca2+ (up to 1mm). Inhibition of channels could also be induced by millimolar concentrations of Ba2+, Sr2+, or VO2+, but not by Mg2+. The Ca2+ inhibition constant was a strong function of pH, and varied from 0.04 μm at pH 7.8 to 〉10 μm at pH 7.0 Strong pH effects were also demonstrated by measuring the pH dependence of22Na+ uptake in vesicles that contained 0.5 μm Ca2+. This Ca2+ activity produced a maximal inhibition of22Na+ uptake at pH≥7.4 but had no effect at pH≤7.0. The tracer fluxes measured in the absence of Ca2+ were pH independent over this range. The data is compatible with the model that Ca2+ blocks channels by binding to a site composed of several deprotonated groups. The protonation of any one of these groups prevents Ca2+ from binding to this site but does not by itself inhibit transport. The fact that the apical Na+ conductance in vesicles, can effectively be modulated by minor variations of the internal pH near the physiological value, raises the possibility that channels are being regulated by pH changes which alter their apparent affinity to cytoplasmic Ca2+, rather than, or in addition to changes in the cytoplasmic level of free Ca2+.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 77 (1984), S. 213-222 
    ISSN: 1432-1424
    Keywords: basolateral membrane ; current-voltage relations ; nystatin ; potassium transport ; tight epithelia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Exposure of the mucosal side of toad(Bufo bufo) urinary bladder and frog(Rana ridibunda) skin to the polyene ionophore nystatin, resulted in stable preparations in which the apical resistance was negligible compared to the basolateral resistance. The preparations support passive K currents in both directions and an amiloride-insensitive Na current in the apicalserosal direction which is blocked by ouabain. The nystatintreated toad bladder was used to study the electrical properties of the basolateral membrane by means of current-voltage curves recorded transepithelially. The K current showed strong rectification at cellular potentials negative with respect to the interstitial space. The ouabain-sensitive current increased with membrane voltage at negative voltages but saturated above+20 mV.
    Type of Medium: Electronic Resource
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