title: Osmolar regulation of endothelin-1 production by the inner medullary collecting duct.
abstract: OBJECTIVE
  Endothelin-1 (ET-1) is an autocrine inhibitor of collecting duct (CD) Na(+) and water reabsorption. CD ET-1 production is increased by a high salt diet and is important in promoting a natriuretic response. The mechanisms by which a high salt diet enhances CD ET-1 are being uncovered. In particular, elevated tubule fluid flow, as occurs in salt loading, enhances CD ET-1 synthesis. Tubule fluid solute content and interstitial osmolality can also be altered by a high salt diet, however their effect on CD ET-1 alone, or in combination with flow, is poorly understood.
  
  
  METHODS
  ET-1 mRNA production by a mouse inner medullary CD cell line (mIMCD3) in response to changing flow and/or osmolality was assessed.
  
  
  RESULTS
  Flow or hyperosmolality (using NaCl, mannitol or urea) individually caused an ~2-fold increase in ET-1 mRNA, while flow and hyperosmolality together increased ET-1 mRNA by ~14 fold. The hyperosmolality effect alone and the synergistic effect of flow + hyperosmolality was inhibited by chelation of intracellular Ca(2+), however were not altered by blockade of downstream Ca(2+)-signaling pathways (calcineurin or NFATc), inhibition of cellular Ca(2+) entry channels (purinergic receptors or polycystin-2), or blockade of the epithelial Na(+) channel. Inhibition of NFAT5 with rottlerin or NFAT5 siRNA greatly reduced the stimulatory effect of osmolality alone and osmolality + flow on mIMCD3 ET-1 mRNA levels.
  
  
  CONCLUSIONS
  Both flow and osmolality individually and synergistically stimulate mIMCD3 ET-1 mRNA content. These findings may be relevant to explaining high salt diet induction of CD ET-1 production.
authors.affiliation: Division of Nephrology, University of Utah Health Sciences Center, Salt Lake City, UT, USA; Department of Pharmaceutics and Pharmaceutical Chemistry, Salt Lake City, UT, USA.
authors.forename: Meghana M
authors.initials: MM
authors.lastname: Pandit
authors.affiliation: Division of Nephrology, University of Utah Health Sciences Center, Salt Lake City, UT, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Division of Nephrology, University of Utah Health Sciences Center, Salt Lake City, UT, USA.
authors.forename: Alfred
authors.initials: A
authors.lastname: van Hoek
authors.affiliation: Division of Nephrology, University of Utah Health Sciences Center, Salt Lake City, UT, USA; Department of Pharmaceutics and Pharmaceutical Chemistry, Salt Lake City, UT, USA; Salt Lake Veterans Affairs Medical Center, Salt Lake City, UT, USA. Electronic address: donald.kohan@hsc.utah.edu.
authors.forename: Donald E
authors.initials: DE
authors.lastname: Kohan
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D019332:Endothelin-1 / Q000096:biosynthesis* / Q000235:genetics; D007679:Kidney Medulla / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D051379:Mice; D009994:Osmolar Concentration; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D019332:Endothelin-1; D012333:RNA, Messenger; D002118:Calcium
keywords: Collecting duct; Endothelin; Flow; Osmolality