Glucocorticoid regulation of genes in the amiloride-sensitive sodium transport pathway by semicircular canal duct epithelium of neonatal rat

• Published in: Physiological genomics 2006-01, Vol.24 (2), p.114-123
• Main Authors: Pondugula, Satyanarayana R, Raveendran, Nithya N, Ergonul, Zuhal, Deng, Youping, Chen, Jun, Sanneman, Joel D, Palmer, Lawrence G, Marcus, Daniel C
• Format: Article
• Language: English
• Subjects: 11-beta-Hydroxysteroid Dehydrogenases - metabolism; Amiloride - pharmacology; Animals; Animals, Newborn; Biological Transport - drug effects; Cation Transport Proteins - genetics; Cells, Cultured; Dimethyl Sulfoxide - pharmacology; Endosomal Sorting Complexes Required for Transport; Epithelial Sodium Channels - metabolism; Epithelium - drug effects; Epithelium - metabolism; Gene Expression Regulation - drug effects; Glucocorticoids - pharmacology; Immediate-Early Proteins - genetics; Nedd4 Ubiquitin Protein Ligases; Protein-Serine-Threonine Kinases - genetics; Rats; Rats, Wistar; Receptors, Glucocorticoid - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Semicircular Canals - metabolism; Sodium - metabolism; Ubiquitin-Protein Ligases - genetics
• ISSN: 1094-8341; 1531-2267
• DOI: 10.1152/physiolgenomics.00006.2005

1 Cellular Biophysics Laboratory, Department of Anatomy and Physiology 2 Division of Biology, Bioinformatics Center, Kansas State University, Manhattan, Kansas 3 Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York The lumen of the inner ear has an unusually low concentration of endolymphatic Na + , which is important for transduction processes. We have recently shown that glucocorticoid receptors (GR) stimulate absorption of Na + by semicircular canal duct (SCCD) epithelia. In the present study, we sought to determine the presence of genes involved in the control of the amiloride-sensitive Na + transport pathway in rat SCCD epithelia and whether their level of expression was regulated by glucocorticoids using quantitative real-time RT-PCR. Transcripts were present for -, ß-, and -subunits of the epithelial sodium channel (ENaC); the 1 -, 3 -, ß 1 -, and ß 3 -isoforms of Na + -K + -ATPase; inwardly rectifying potassium channels [IC 50 of short circuit current ( I sc ) for Ba 2+ : 210 µM] Kir2.1, Kir2.2, Kir2.3, Kir2.4, Kir3.1, Kir3.3, Kir4.1, Kir4.2, Kir5.1, and Kir7.1; sulfonyl urea receptor 1 (SUR1); GR; mineralocorticoid receptor (MR); 11ß-hydroxysteroid dehydrogenase (11ß-HSD) types 1 and 2; serum- and glucocorticoid-regulated kinase 1 (Sgk1); and neural precursor cell-expressed developmentally downregulated 4-2 (Nedd4-2). On the other hand, transcripts for the 4 -subunit of Na + -K + -ATPase, Kir1.1, Kir3.2, Kir3.4, Kir6.1, Kir6.2, and SUR2 were found to be absent, and I sc was not inhibited by glibenclamide. Dexamethasone (100 nM for 24 h) not only upregulated the transcript expression of -ENaC ( 4-fold), ß 2 -subunit ( 2-fold) and ß 3 -subunit ( 8-fold) of Na + -K + -ATPase, Kir2.1 ( 5-fold), Kir2.2 ( 9-fold), Kir2.4 ( 3-fold), Kir3.1 ( 3- fold), Kir3.3 ( 2-fold), Kir4.2 ( 3-fold ), Kir7.1 ( 2-fold), Sgk1 ( 4-fold), and Nedd4-2 ( 2-fold) but also downregulated GR ( 3-fold) and 11ß-HSD1 ( 2-fold). Expression of GR and 11ß-HSD1 was higher than MR and 11ß-HSD2 in the absence of dexamethasone. Dexamethasone altered transcript expression levels ( -ENaC and Sgk1) by activation of GR but not MR. Proteins were present for the -, ß-, and -subunits of ENaC and Sgk1, and expression of - and -ENaC was upregulated by dexamethasone. These findings are consistent with the genomic stimulation by glucocorticoids of Na + absorption by SCCD and provide an understanding of the therapeutic action of glucocorticoids in