title: Reduced expression of Na-K-2Cl cotransporter in medullary TAL in vitamin D-induced hypercalcemia in rats.
abstract: Chronic hypercalcemia (HC) is accompanied by urinary concentration defects, and functional studies indicate defects in the thick ascending limb (TAL). We hypothesize that dysregulation of renal sodium transporters may play an important role in this. Vitamin D-induced HC in rats resulted in polyuria, natriuresis, and phosphaturia. Immunoblotting revealed a marked reduction in the abundance of rat type 1 bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1) in inner stripe of the outer medullary (ISOM; 36 +/- 5%) and whole kidney (51 +/- 11%) in HC. Consistent with this finding, immunocytochemistry and immunoelectron microscopy demonstrated reduced BSC-1 labeling of the apical plasma membrane. Immunoblotting and immunohistochemical labeling of the K channel Kir 1.1 (ROMK) was also reduced in HC. In contrast, there were no reductions in the expression of Na/H exchanger (NHE)3 and Na,K-ATPase in ISOM. The abundance of the proximal tubule type II Na-P(i) cotransporter (NaPi-2) (but not Na,K-ATPase and NHE3) was significantly reduced (25 +/- 4%), consistent with a dramatic increase in urinary phosphate excretion. In conclusion, 1) the reduced abundance of BSC-1 and ROMK in TAL is likely to play a major role in the urinary concentration defects associated with HC and 2) the reduced abundance of NaPi-2 is likely to play a role in the increased urinary phosphate excretion.
authors.affiliation: Water and Salt Research Center, University of Aarhus, DK-8000 Aarhus C, Denmark.
authors.forename: Weidong
authors.initials: W
authors.lastname: Wang
authors.forename: Tae-Hwan
authors.initials: TH
authors.lastname: Kwon
authors.forename: Chunling
authors.initials: C
authors.lastname: Li
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; D006934:Hypercalcemia / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D015151:Immunoblotting; D007150:Immunohistochemistry; D007671:Kidney Concentrating Ability / Q000502:physiology*; D007679:Kidney Medulla / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D007687:Kidney Tubules, Proximal / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D008138:Loop of Henle / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D016253:Microscopy, Immunoelectron; D009318:Natriuresis / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D011141:Polyuria / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D015221:Potassium Channels / Q000032:analysis / Q000096:biosynthesis; D024661:Potassium Channels, Inwardly Rectifying; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000032:analysis; D028021:Sodium-Potassium-Chloride Symporters / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D064466:Solute Carrier Family 12, Member 1; D014807:Vitamin D; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: C510692:Kcnj1 protein, rat; D010710:Phosphates; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; C578716:Slc12a1 protein, rat; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D014807:Vitamin D; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase