Regulation by glucocorticoids and osmolality of expression of ROMK (Kir 1.1), the apical K channel of thick ascending limb.
Mechanisms of regulation of ROMK channel mRNA and protein expression in medullary thick ascending limb (MTAL) were assessed in rat MTAL fragments incubated for 7 h. ROMK mRNA was quantified by quantitative RT-PCR and ROMK protein by immunoblotting analysis of crude membranes. Medium hyperosmolality (450 mosmol/kgH(2)O; NaCl plus urea added to isoosmotic medium) increased ROMK mRNA (P < 0.04) and protein (P < 0.006), and 10 nM dexamethasone also increased ROMK mRNA (P < 0.02). Hyperosmolality and dexamethasone had no additive effects on ROMK mRNA. NaCl alone, but not urea or mannitol, reproduced the hyperosmolality effect on ROMK mRNA. 1-Deamino-(8-d-arginine) vasopressin (1 nM) or 0.5 mM 8-bromo-cAMP had no effect per se on ROMK mRNA and protein. However, 8-bromo-cAMP abolished the stimulatory effect of dexamethasone on ROMK mRNA in the isoosmotic but not in the hyperosmotic medium (P < 0.004). In in vivo studies, the abundance of ROMK protein and mRNA increased in adrenalectomized (ADX) rats infused with dexamethasone compared with ADX rats (P < 0.02). These results establish glucocorticoids and medium NaCl concentration as direct regulators of MTAL ROMK mRNA and protein expression, which may be modulated by cAMP-dependent factors.
Gallazzini
Morgan
M
Institut National de la Santé et de la Recherche Médicale U.426, Institut Fédératif Régional Claude Bernard, Faculté de Médecine Xavier Bichat, Université Paris 7, 75018 Paris, France.
Attmane-Elakeb
Amel
A
Mount
David B
DB
Hebert
Steven C
SC
Bichara
Maurice
M
D000315:Adrenalectomy; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D005938:Glucocorticoids / Q000494:pharmacology*; D066298:In Vitro Techniques; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D015221:Potassium Channels / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012965:Sodium Chloride / Q000008:administration & dosage
D003470:Culture Media; D005938:Glucocorticoids; C510692:Kcnj1 protein, rat; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D012965:Sodium Chloride; D003907:Dexamethasone