Dexamethasone and cyclic AMP regulate sodium phosphate cotransporter (NaPi-IIb and Pit-1) mRNA and phosphate uptake in rat alveolar type II epithelial cells.
Alveolar epithelial type II (AT II) cells need phosphate (Pi) for surfactant synthesis. The Na-dependent (Na(d)) Pi transporters NaPi-IIb and Pit-1 are expressed in lung, but their expression, regulation, and function in AT II cells remain unclear. We studied NaPi-IIb and Pit-1 mRNA expression in cultured AT II cells isolated from adult rat lung, their regulation by agents known to enhance surfactant production, dexamethasone (dex) and dibutyryl cyclic AMP (cAMP), and the effects of dex and cAMP on Na(d) Pi uptake by this cell type. By Northern analysis, cultured AT II cells expressed both NaPi-IIb (4.8 and 4.0 kb) and Pit-1 (4.3 kb) mRNA. Treatment with 100 nmol/l dex for 24 h decreased the expression of both mRNAs (to 0.48 +/- 0.06 and 0.77 +/- 0.05, respectively, as compared to control), while 0.1 mmol/l cAMP stimulated NaPi-IIb (1.94 +/- 0.22) but not Pit-1 mRNA (0.90 +/- 0.05, compared to vehicle-treated cells). NaPi-IIb and Pit-1 proteins could not be identified by western analysis of plasma membrane preparations of cultured AT II cells. AT II cells take up Pi in a Na(d) manner. Uptake was slightly (to 0.78-fold of the control) decreased by 100 nmol/l dex but not affected by 0.1 mmol/l cAMP treatment. Although NaPi-IIb mRNA expression was maintained to some extent by AT II cells kept in primary culture, Pi uptake was more closely related to Pit-1 mRNA expression.
Jin
Chengluo
C
Division of Endocrinology and Diabetology, Department of Internal Medicine, University Hospital, 8091, Zurich, Switzerland.
Zoidis
Evangelos
E
Ghirlanda
Claudia
C
Schmid
Christoph
C
D000818:Animals; D001692:Biological Transport; D015152:Blotting, Northern; D015153:Blotting, Western; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002794:Choline / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D050611:Sodium-Phosphate Cotransporter Proteins, Type III / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
D010710:Phosphates; D012333:RNA, Messenger; C493588:Slc20a1 protein, rat; C493559:Slc34a2 protein, rat; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb; D003907:Dexamethasone; D012964:Sodium; D000242:Cyclic AMP; D002794:Choline