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Delayed shrinkage triggered by the Na + –K + pump in terbutaline‐stimulated rat alveolar type II cells
Author(s) -
Hosoi Keita,
Min KyongYob,
Iwagaki Akitaka,
Murao Hitoshi,
Hanafusa Toshiaki,
Shimamoto Chikao,
Katsu Kenichi,
Kato Masumi,
Fujiwara Shoko,
Nakahari* Takashi
Publication year - 2004
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2003.026617
Subject(s) - ouabain , tetraethylammonium , chemistry , depolarization , quinidine , ionophore , valinomycin , biophysics , channel blocker , hyperpolarization (physics) , membrane potential , ion transporter , membrane , sodium , potassium , medicine , stereochemistry , biochemistry , calcium , organic chemistry , nuclear magnetic resonance spectroscopy , biology
Terbutaline (10 μ m ) induced a triphasic volume change in alveolar type II (AT‐II) cells: an initial shrinkage (initial phase) followed by cell swelling (second phase) and a gradual shrinkage (third phase). The present study demonstrated that the initial and the third phases are evoked by the activation of K + and Cl − channels and the second phase is evoked by the activation of Na + and Cl − channels. Ouabain blocked the third phase, although it did not block the initial and second phases. This suggests that the third phase is triggered by the Na + –K + pump. Tetraethylammonium (TEA, a K + channel blocker) decreased the volume of AT‐II cells and enhanced the terbutaline‐stimulated third phase, although quinidine, another K + channel blocker, increased the volume of AT‐II cells. The TEA‐induced cell shrinkage was inhibited by ouabain, suggesting that TEA increases Na + –K + pump activity. Ba 2+ , 2,3‐diaminopyridine and a high [K + ] o (30 m m ) similarly decreased the volume of AT‐II cells. These findings suggest that depolarization induced by TEA increases Na + –K + pump activity, which increases [K + ] i . This [K + ] i increase, in turn, hyperpolarizes membrane potential. Valinomycin (a K + ionophore), which induces hyperpolarization, decreased the volume of AT‐II cells and enhanced the third phase in these cells. In conclusion, in terbutaline‐stimulated AT‐II cells, an increase in Na + –K + pump activity hyperpolarizes the membrane potential and triggers the third phase by switching net ion transport from NaCl entry to KCl release.