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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 61 (1981), S. 127-134 
    ISSN: 1432-1424
    Keywords: Frog skin ; microelectrodes ; membrane potentials ; intracellular activities ; amiloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Intracellular Na+, K+, and Cl− activities (a Na i ,a K i ,a Cl i ) and transapical membrane potentials (V o) were measured with liquid ion-exchanger and open-tip microelectrodes in isolated short-circuited frog skins (R. pipiens) incubated at 23°C in normal amphibian Ringer's solution. Under control conditionsa Na i =14±3mm,a K i =132±10mm anda Cl i =18±3mm (sd). The value ofa Cl i is 4.4 times the value corresponding to electrochemical equilibrium for this ion. Thus, Cl− is actively accumulated by epithelial cells of the frog skin. Shortly after addition of amiloride (2–5 μm) to the apical bathing medium,a K i ,a Na i , anda Cl i were essentially unchanged althoughV o had hyperpolarized by about 30–40 mV. During long-term exposure to amiloridea K i anda Cl i did not change significantly,V o depolarized by about 16 mV from the maximal value anda Na i decreased to 8±3mm. Immediately after exposure to amiloride the transmembrane driving force for Na+ increased from 124 to 154 mV. During further exposure to amiloride, despite changes in bothV o anda Na i , this driving force remained virtually constant. SinceI sc during this period was close to zero, it is suggested that the observed driving force for Na+ under these conditions approximates the maximal driving force generated by the Na+−K+ ATP-ase pump in the basolateral cell membrane.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 399 (1983), S. 336-341 
    ISSN: 1432-2013
    Keywords: Frog skin ; Junctional conductance ; Voltagedivider ratio ; Paracellular conductance ; Membrane conductances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It has been suggested that distribution of lateral interspace resistance in association with a highly conductive junction can significantly affect the measurement of outer membrane(o)/epithelial(t) voltage divider ratios (F o=δV o/δV t), thereby leading to erroneous inferences regarding the outer membrane fractional resistance [fR o=R o/R c=R o/(R o+R i)], whereR o andR i are the outer and inner cell membrane resistance respectively andR c is the total cell membrane resistance. We present here experimental evidence for this point of view. During seasons when frog skins were highly permeable to Cl, transepithelial conductanceg t often exceeded 2 mS/cm2. High concentrations of external amiloride rapidly blocked cellular transport, butg t initially remained high andF o remained appreciably less than 1.0. These values ofF o were found here to result from low junctional resistanceR j: increase ofR j, either gradually following the administration of amiloride, or abruptly with external replacement of Cl by other anions, was associated with increase ofF o to near unity, without effect on the membrane potential or significant change in the short-circuit current. Experimental results following amiloride validated a simple equivalent circuit model predicting near-linear increase inF o with progressive decrease ing t and led to plausible values ofR j and lateral space resistanceR l. The possible influence of the paracellular resistance pattern on the evaluation of cell membrane resistances from voltage divider ratios is discussed.
    Type of Medium: Electronic Resource
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