Summary
Intracellular Na+, K+, and Cl− activities (a iNa ,a iK ,a iCl ) 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 iNa =14±3mm,a iK =132±10mm anda iCl =18±3mm (sd). The value ofa iCl 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 iK ,a iNa , anda iCl were essentially unchanged althoughV o had hyperpolarized by about 30–40 mV. During long-term exposure to amiloridea iK anda iCl did not change significantly,V o depolarized by about 16 mV from the maximal value anda iNa 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 iNa , 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.
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Nagel, W., Garcia-Diaz, J.F. & Armstrong, W.M. Intracellular ionic activities in frog skin. J. Membrain Biol. 61, 127–134 (1981). https://doi.org/10.1007/BF02007639
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DOI: https://doi.org/10.1007/BF02007639