title: Variations of dietary salt and fluid modulate calcium and magnesium transport in the renal distal tubule.
abstract: BACKGROUND
  The renal distal tubule fine-tunes renal epithelial calcium transport. Dietary intake of salt and fluid varies day-to-day and the kidney adapts accordingly to maintain homeostasis. The alternations in salt and fluid balance affect calcium and magnesium transport in the distal tubule, but the mechanisms are not fully understood.
  
  
  METHODS
  Sprague-Dawley rats were grouped into high-salt, low-salt and dehydration treatment. Daily intake, water consumption and urine output were recorded. At the end of the experiment, blood and urine samples were collected for hormonal and biochemical tests. Genetic analysis, immunoblotting and immunofluorescence studies were then performed to assess the alterations of calcium and magnesium transport-related molecules.
  
  
  RESULTS
  High-salt treatment increased urinary sodium, calcium and magnesium excretion. Low-salt treatment and dehydration were associated with decreased urinary excretion of all electrolytes. High-salt treatment was associated with increased intact parathyroid hormone levels. A significant increase in gene expression of TRPV5, TRPV6, calbindin-D28k and TRPM6 was found during high-salt treatment, while low salt and dehydration diminished expression. These findings were confirmed with immunofluorescence studies. High-salt and low-salt intake or dehydration did not cause any significant changes in WNK1, WNK3 and WNK4.
  
  
  CONCLUSIONS
  Alternations in salt and water intake affect renal calcium and magnesium handling. High-salt intake increases the distal delivery of the divalent cations which upregulates distal tubule calcium and magnesium transport molecules, while the opposite effects are associated with low-salt intake or dehydration.
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Kaohsiung Chang-Gung Memorial Hospital, Chang-Gung University College of Medicine, Kaohsiung, Taiwan.
authors.forename: Chien-Te
authors.initials: CT
authors.lastname: Lee
authors.forename: Yeong-Hau H
authors.initials: YH
authors.lastname: Lien
authors.forename: Li-Wen
authors.initials: LW
authors.lastname: Lai
authors.forename: Hwee-Yeong
authors.initials: HY
authors.lastname: Ng
authors.forename: Terry Ting-Yu
authors.initials: TT
authors.lastname: Chiou
authors.forename: Hung-Chun
authors.initials: HC
authors.lastname: Chen
mesh_terms: D000818:Animals; D064092:Calbindin 1 / Q000235:genetics* / Q000378:metabolism; D002118:Calcium / Q000652:urine; D015220:Calcium Channels / Q000378:metabolism*; D004326:Drinking; D005786:Gene Expression Regulation; D007686:Kidney Tubules, Distal / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism* / Q000652:urine; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000652:urine; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage* / Q000378:metabolism; D050053:TRPM Cation Channels / Q000235:genetics* / Q000378:metabolism; D050916:TRPV Cation Channels / Q000235:genetics* / Q000378:metabolism
chemical_list: D064092:Calbindin 1; D015220:Calcium Channels; D010281:Parathyroid Hormone; D017673:Sodium Chloride, Dietary; D050053:TRPM Cation Channels; C507531:TRPM6 protein, rat; D050916:TRPV Cation Channels; D012964:Sodium; D008274:Magnesium; D002118:Calcium