Delayed shrinkage triggered by the Na+–K+ pump in terbutaline-stimulated rat alveolar type II cells

• Published in: Experimental physiology 2004-07, Vol.89 (4), p.373-385
• Main Authors: Hosoi, Keita, Min, Kyong‐Yob, Iwagaki, Akitaka, Murao, Hitoshi, Hanafusa, Toshiaki, Shimamoto, Chikao, Katsu, Ken‐ichi, Kato, Masumi, Fujiwara, Shoko, Nakahari, Takashi
• Format: Article
• Language: English
• Subjects: Amiloride - analogs & derivatives; Amiloride - pharmacology; Animals; Enzyme Inhibitors - pharmacology; Ionophores - pharmacology; Male; Ouabain - pharmacology; Potassium - pharmacokinetics; Potassium Channel Blockers - pharmacology; Pulmonary Alveoli - cytology; Pulmonary Alveoli - metabolism; Rats; Rats, Wistar; Sodium - pharmacokinetics; Sodium Channel Blockers - pharmacology; Sodium-Potassium-Exchanging ATPase - antagonists & inhibitors; Sodium-Potassium-Exchanging ATPase - metabolism; Sympathomimetics - pharmacology; Terbutaline - pharmacology; Tetraethylammonium - pharmacology; Valinomycin - pharmacology; Water-Electrolyte Balance - drug effects; Water-Electrolyte Balance - physiology
• ISSN: 0958-0670; 1469-445X
• DOI: 10.1113/expphysiol.2003.026617

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.