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  • Title: Delayed shrinkage triggered by the Na+-K+ pump in terbutaline-stimulated rat alveolar type II cells.
    Author: Hosoi K, Min KY, Iwagaki A, Murao H, Hanafusa T, Shimamoto C, Katsu K, Kato M, Fujiwara S, Nakahari T.
    Journal: Exp Physiol; 2004 Jul; 89(4):373-85. PubMed ID: 15123552.
    Abstract:
    Terbutaline (10 microm) 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. Ba2+, 2,3-diaminopyridine and a high [K+]o (30 mm) 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.
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