title: Segment-specific ENaC downregulation in kidney of rats with lithium-induced NDI.
abstract: Lithium-induced nephrogenic diabetes insipidus is associated with increased renal sodium excretion in addition to severe urinary concentrating defects. However, the molecular basis for this altered renal sodium excretion remains undefined. The amiloride-sensitive sodium channel (ENaC) is expressed in the renal connecting tubule and collecting duct and is essential in renal regulation of body sodium balance and blood pressure. We hypothesized that dysregulation of ENaC subunits may be responsible for the increased sodium excretion associated with lithium treatment. Lithium treatment for 28 days resulted in severe polyuria, increased fractional excretion of sodium, and increased plasma aldosterone concentration. Immunoblotting revealed that lithium treatment induced a marked decrease in the protein abundance of beta-ENaC and gamma-ENaC in the cortex and outer medulla. Moreover, immunohistochemistry and laser confocal microscopy demonstrated an almost complete absence of beta-ENaC and gamma-ENaC labeling in cortical and outer medullary collecting duct, which was not affected by dietary sodium intake. In contrast, immunohistochemistry showed increased apical labeling of all ENaC subunits in the connecting tubule and inner medullary collecting duct in rats on a fixed sodium intake but not in rats with free access to sodium. Except for a modest downregulation of the thiazide-sensitive Na-Cl cotransporter, the key renal sodium transporters upstream from the connecting tubule (including the alpha1-subunit of Na-K-ATPase, type 3 Na/H exchanger, and Na-K-2Cl cotransporter) were unchanged. These results identify a marked and highly segment-specific downregulation of beta-ENaC and gamma-ENaC in the cortical and outer medullary collecting duct, chief sites for collecting duct sodium reabsorption, in rats with a lithium-induced increase in fractional excretion of sodium.
authors.affiliation: The Water and Salt Research Center, Institute of Anatomy (Bldg. 233), University of Aarhus, DK-8000 Aarhus, Denmark.
authors.forename: Jakob
authors.initials: J
authors.lastname: Nielsen
authors.forename: Tae-Hwan
authors.initials: TH
authors.lastname: Kwon
authors.forename: Jeppe
authors.initials: J
authors.lastname: Praetorius
authors.forename: Young-Hee
authors.initials: YH
authors.lastname: Kim
authors.forename: Jørgen
authors.initials: J
authors.lastname: Frøkiaer
authors.forename: Mark A
authors.initials: MA
authors.lastname: Knepper
authors.forename: Søren
authors.initials: S
authors.lastname: Nielsen
mesh_terms: D000818:Animals; D018500:Diabetes Insipidus, Nephrogenic / Q000139:chemically induced / Q000378:metabolism*; D015536:Down-Regulation; D053503:Epithelial Sodium Channels; D006977:Hypertension, Renal / Q000139:chemically induced / Q000378:metabolism; D007150:Immunohistochemistry; D007672:Kidney Cortex / Q000378:metabolism; D007679:Kidney Medulla / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008094:Lithium; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D064466:Solute Carrier Family 12, Member 1
chemical_list: D053503:Epithelial Sodium Channels; C578716:Slc12a1 protein, rat; D015222:Sodium Channels; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D008094:Lithium; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase