title: Glucocorticoid regulation of genes in the amiloride-sensitive sodium transport pathway by semicircular canal duct epithelium of neonatal rat.
abstract: 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 alpha-, beta-, and gamma-subunits of the epithelial sodium channel (ENaC); the alpha1-, alpha3-, beta1-, and beta3-isoforms of Na+-K+-ATPase; inwardly rectifying potassium channels [IC50 of short circuit current (Isc) for Ba2+: 210 microM] 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); 11beta-hydroxysteroid dehydrogenase (11beta-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 alpha4-subunit of Na+-K+-ATPase, Kir1.1, Kir3.2, Kir3.4, Kir6.1, Kir6.2, and SUR2 were found to be absent, and Isc was not inhibited by glibenclamide. Dexamethasone (100 nM for 24 h) not only upregulated the transcript expression of alpha-ENaC (approximately 4-fold), beta2-subunit (approximately 2-fold) and beta3-subunit (approximately 8-fold) of Na+-K+-ATPase, Kir2.1 (approximately 5-fold), Kir2.2 (approximately 9-fold), Kir2.4 (approximately 3-fold), Kir3.1 (approximately 3- fold), Kir3.3 (approximately 2-fold), Kir4.2 (approximately 3-fold), Kir7.1 (approximately 2-fold), Sgk1 (approximately 4-fold), and Nedd4-2 (approximately 2-fold) but also downregulated GR (approximately 3-fold) and 11beta-HSD1 (approximately 2-fold). Expression of GR and 11beta-HSD1 was higher than MR and 11beta-HSD2 in the absence of dexamethasone. Dexamethasone altered transcript expression levels (alpha-ENaC and Sgk1) by activation of GR but not MR. Proteins were present for the alpha-, beta-, and gamma-subunits of ENaC and Sgk1, and expression of alpha- and gamma-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 the treatment of Meniere's disease.
authors.affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas 66506-5802, USA.
authors.forename: Satyanarayana R
authors.initials: SR
authors.lastname: Pondugula
authors.forename: Nithya N
authors.initials: NN
authors.lastname: Raveendran
authors.forename: Zuhal
authors.initials: Z
authors.lastname: Ergonul
authors.forename: Youping
authors.initials: Y
authors.lastname: Deng
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.forename: Joel D
authors.initials: JD
authors.lastname: Sanneman
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Palmer
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Marcus
mesh_terms: D042842:11-beta-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001692:Biological Transport / Q000187:drug effects; D027682:Cation Transport Proteins / Q000235:genetics; D002478:Cells, Cultured; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D017874:Immediate-Early Proteins / Q000235:genetics; D000075702:Nedd4 Ubiquitin Protein Ligases; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D012665:Semicircular Canals / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D042842:11-beta-Hydroxysteroid Dehydrogenases; D000584:Amiloride; D027682:Cation Transport Proteins; D004121:Dimethyl Sulfoxide; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D005938:Glucocorticoids; D017874:Immediate-Early Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D012964:Sodium; D044767:Ubiquitin-Protein Ligases; D000099184:Serum-Glucocorticoid Regulated Kinases; C000618479:NEDD4L protein, rat; C000618484:Nedd4 protein, rat