Alveolar Epithelial Ion and Fluid Transport Na transport proteins are expressed by rat alveolar epithelial type I cells

Borok, Zea, Janice M. Liebler, Richard L. Lubman, Martha J. Foster, Beiyun Zhou, Xian Li, Stephanie M. Zabski, Kwang-Jin Kim, and Edward D. Crandall. Na transport proteins are expressed by rat alveolar epithelial type I cells. Am J Physiol Lung Cell Mol Physiol 282: L599–L608, 2002; 10.1152/ajplung.00130.2000.—Despite a presumptive role for type I (AT1) cells in alveolar epithelial transport, specific Na transporters have not previously been localized to these cells. To evaluate expression of Na transporters in AT1 cells, double labeling immunofluorescence microscopy was utilized in whole lung and in cytocentrifuged preparations of partially purified alveolar epithelial cells (AEC). Expression of Na pump subunit isoforms and the -subunit of the rat (r) epithelial Na channel ( -ENaC) was evaluated in isolated AT1 cells identified by their immunoreactivity with AT1 cell-specific antibody markers (VIIIB2 and/or anti-aquaporin-5) and lack of reactivity with antibodies specific for AT2 cells (anti-surfactant protein A) or leukocytes (anti-leukocyte common antigen). Expression of the Na pump 1-subunit in AEC was assessed in situ. Na pump subunit isoform and -rENaC expression was also evaluated by RT-PCR in highly purified ( 95%) AT1 cell preparations. Labeling of isolated AT1 cells with anti1 and anti1 Na pump subunit and anti-rENaC antibodies was detected, while reactivity with anti2 Na pump subunit antibody was absent. AT1 cells in situ were reactive with anti1 Na pump subunit antibody. Na pump 1and 1(but not 2-) subunits and -rENaC were detected in highly purified AT1 cells by RT-PCR. These data demonstrate that AT1 cells express Na pump and Na channel proteins, supporting a role for AT1 cells in active transalveolar epithelial Na transport.