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Changes in intracellular pH (pHi) of alveolar type II (ATII) cells have been involved in the pathophysiology of pulmonary edema. ATII cells have evolved several ions transporters to regulate their pHi, including a Na + H + antiporter. Because halothane alters the activity of ion transporters in various cells types, it may also affect the activity of this Na + H + antiporter. This study was performed 1) to characterize a Na + H + antiporter in a model of ATII cells and 2) to investigate the effect of halothane on the activity of this antiporter. ATII cells were obtained from primary rat ATII cells transfected with a mutant of simian virus SV40 large T antigen (SV40-T2), and their pHi was monitored using the pH-sensitive fluorescent probe 2'-7' (bis carboxyethyl)-5(6')-carboxyfluorescein. We demonstrated in vitro that 1) a Na + H + antiporter (apparent Km 6.8 n 3.4 mM, Vmax 0.0105 n 0.0013 ΔUpHi/s) regulates the pHi of SV40-T2 cells and 2) at clinically relevant concentrations (10 -3 to 10 -5 M) and for a short exposure duration (60 min), halothane enhances the activity of this antiporter. Because ATII cell acidification has been associated with alterations in the alveolar epithelial barrier, halothane-induced intracellular alkalinization might exhibit some protective effect in clinical situations, such as aspiration pneumonia. Implications: In vitro, halothane induces an intracellular alkalinization of pneumocytes II via the activation of a Na + H + antiporter. Because acidification of these cells has been associated with alterations in the alveolar epithelial barrier, halothane might exhibit some protective effect in clinical situations, such as aspiration pneumonia.

Background Halothane alters surfactant biosynthesis and metabolism of alveolar type II cells. In addition to synthesizing surfactant, alveolar type II cells actively transport sodium (Na) from the alveolar space to the interstitium. Na enters the cells through amiloride-sensitive Na channels or Na cotransporters and is extruded by a Na pump. The purpose of this study was to examine the effects of halothane on Na transport activities. Methods Epithelial type II cells from adult rat lungs were exposed to halothane concentrations of 1, 2, and 4% from 0.5-4 h. In some experiments, cells that were exposed to 1% halothane for 1 h were allowed to recover after replacement of the medium for 15 and 30 min. Na transport was then evaluated by direct measurement of radiolabeled ions uptake. In addition, the effects of halothane were assessed in the absence of extracellular calcium (Ca) with or without 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an intracellular Ca chelating agent. Results Exposure of epithelial type II cells to halothane reduced the activity of sodium, potassium-adenosine triphosphatase, and amiloride-sensitive Na channels, whereas Na cotransporters were unchanged. The decrease in sodium, potassium-adenosine triphosphatase activity was maximal for 30 min of exposure and reached 50, 42, and 56% for halothane concentrations of 1, 2, and 4%, respectively, and did not change for longer exposure times. This effect was not prevented by either the absence of extracellular Ca or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid pretreatment. Exposure for 45 min to 1% halothane also decreased Na channel activity by 46%. These effects were completely reversible after 30 min of recovery. Conclusions Sodium, potassium-adenosine triphosphatase, and amiloride-sensitive Na channel activities are impaired by halothane in alveolar type II cells in vitro. This inhibition could reduce transepithelial Na transport.