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Am J Physiol Renal Physiol (January 21, 2003). doi:10.1152/ajprenal.00255.2002
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Submitted on July 16, 2002
Accepted on January 16, 2003

Regulation by glucocorticoids and osmolality of expression of ROMK (Kir 1.1), the apical K channel of thick ascending limb

Morgan Gallazzini1, Amel Attmane-Elakeb1, David B. Mount2, Steven C. Hebert3, and Maurice Bichara1*

1 Faculte de Medecine Xavier Bichat, INSERM U.426, Institut Federatif Regional Claude Bernard, Paris, France
2 Harvard Medical School, Renal Division, West Roxbury VA Medical Center and Brigham and Women's Hospital, Boston, Massachusetts, USA
3 Yale University School of Medicine, Department of Cellular and Molecular Physiology, New Haven, Connecticut, USA

* To whom correspondence should be addressed. E-mail: bichara{at}bichat.inserm.fr.

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 mOsm; 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<0.05). 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<0.05). 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.




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