Differential expression of Na-K-ATPase isoforms in rat alveolar epithelial cells.
Lung Na-K-ATPase has been shown to contribute to vectorial Na+ transport and edema clearance. The alpha 1- and beta 1-Na-K-ATPase subunits have been localized to alveolar type II (ATII) cells, and the alpha 2-Na-K-ATPase has been reported in rat lung homogenates. Expression of Na-K-ATPase alpha 1-, alpha 2-, and beta 1-subunits was investigated in rat ATII cells cultured for 7 days, a period during which they lose their phenotypic markers and differentiate to an alveolar type I (ATI)-like cell phenotype. Differentiation of ATII cells to an ATI-like phenotype resulted in a decrease of alpha 1- and an increase of alpha 2-mRNA and protein abundance without changes in the beta 1-subunit. Thus ATI-like cells exhibited a mixture of alpha 1- and alpha 2-isoforms. Nuclear run-on analysis suggests that these changes were transcriptionally regulated. The existence of the distinct functional classes of Na-K-ATPase in ATII and ATI-like cells was confirmed by ouabain inhibition of Na-K-ATPase activity. Ouabain inhibition of ATII cells was consistent with expression of the alpha 1-isozyme [50% inhibitory concentration (IC50) = 4 x 10(-5) M], whereas, in ATI-like cells, it was consistent with the presence of both alpha 1- and alpha 2-isozymes (IC50 = 9.0 x 10(-5) and 1.5 x 10(-7) M, respectively); [3H]ouabain binding studies corroborated these findings. Our results indicate that, during ATII cell cytodifferentiation with time in culture, there is a shift in isoform composition that may reflect physiological functions of alveolar epithelial cells.
Ridge
K M
KM
Department of Pulmonary and Critical Care Medicine, Michael Reese Hospital, Chicago 60616, USA.
Rutschman
D H
DH
Factor
P
P
Katz
A I
AI
Bertorello
A M
AM
Sznajder
J L
JL
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004847:Epithelial Cells; D004848:Epithelium / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007527:Isoenzymes / Q000096:biosynthesis* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology; D010641:Phenotype; D011650:Pulmonary Alveoli / Q000166:cytology / Q000201:enzymology*; D015347:RNA Probes; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis* / Q000378:metabolism; D014158:Transcription, Genetic
D007527:Isoenzymes; D015347:RNA Probes; D012333:RNA, Messenger; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase