RAT LUNG ALVEOLAR TYPE II CELL LINE MAINTAINS SODIUM TRANSPORT CHARACTERISTICS OF PRIMARY CULTURE

Culture of primary alveolar type II cells has been widely used to investigate the Na+ transport characteristics of alveolar epithelium. However, this model was restricted by early morphological and physiological dedifferentiation in culture. Recently, a cell line has been obtained by transfection of neonatal type II cells with the simian virus SV40 large T antigen gene (SV40-T2). SV40-T2 cells have retained proliferative characteristics of the primary type II cells (Clement et al., 1991, Exp. Cell Res., 196:198–205.) In the present study, we have characterized Na+ transport pathways in SV40-T2 cells. SV40-T2 cells retained most cardinal properties of the original alveolar epithelial cells. Na+ entry occurred, as in primary cultures, through both Na+-cotransporters and amiloride-sensitive Na+ channels. SV40-T2 cells expressed Na+-phosphate, Na+-amino acid and Na+-K+-Cl− cotransports which are quantitatively similar to that of primary cultures. The existence of amiloride-sensitive Na+ channels was supported by molecular and functional data. SV40-T2 expressed the cloned α-and γ-mRNAs for the rat epithelial Na+ channel (rENaC), whereas β subunit was not detected, and 22Na+ influx was significantly inhibited by 10 μM amiloride. Na+, which enters SV40-T2 cells, is extruded through a Na+, K+-ATPase: mRNA for α1 and β1 isoforms of Na+, K+-ATPase were present and Na+, K+-ATPase activity was evidenced either on intact cells by the presence of a ouabain-sensitive component of 86Rb+ influx or on cell homogenates by the measurement of ouabain-inhibitable ATP hydrolysis. These results indicate that SV40-T2 cell line displays most of the Na+ transport characteristics of well-differentiated primary cells in the first days of culture. We conclude that the SV40-T2 cell line provides a model of differentiated alveolar type II cells and may be a powerful tool to study, in vitro, the modulation of Na+ transport in pathophysiological conditions. © 1996 Wiley-Liss, Inc.