title: Ciclosporin reduces paracellin-1 expression and magnesium transport in thick ascending limb cells.
abstract: BACKGROUND
  Renal magnesium (Mg2+) wasting is one of the ciclosporin (CsA) tubular effects. The major site of Mg2+ transport is the thick ascending limb (TAL), where 70% of the ultrafiltrable Mg2+ is reabsorbed paracellularly. Paracellin-1 is a tight junction protein, which regulates the paracellular Mg2+ transport in the TAL. We hypothesize that CsA reduces the expression and function of paracellin-1 and accounts for the observed renal Mg2+ wasting.
  
  
  METHODS
  We established an immortalized cultured cortical TAL (cTAL) cell line from L-PK/Tag1 transgenic mice by microdissection. The cultured cells expressed paracellin-1 and the characteristics of cTAL cells. Real-time PCR and western blotting were used to test the CsA effects on paracellin-1 expression of cultured cTAL cells. Cytosolic-free Mg2+ concentration [Mg2+]i change with time in a single cTAL cell was used as an indicator of transcellular Mg2+ transport and assessed by using fluorescence dye Mag-fura-2 AM. Paracellular Mg2+ transport was measured by cells grown in porous filters.
  
  
  RESULTS
  The results showed that CsA significantly reduced paracellin-1 mRNA and protein expression in a dose-dependent manner. CsA (100 ng/ml) incubation for 24 h induced a decrease of paracellin-1 mRNA by 89.4% and paracellin-1 protein by 75.4%. CsA (100 ng/ml) did not change transcellular Mg2+ transport, but paracellular Mg2+ transport was decreased in CsA-treated cTAL cells by 74.4%.
  
  
  CONCLUSIONS
  These results suggested that reduced PCLN-1 expression and paracellular Mg2+ transport might play a role in the renal Mg2+ wasting in the CsA tubular effect.
authors.affiliation: Graduate Institute of Clinical Medical Sciences, Chang Gung University, Taoyuan, and Kidney Research Institue, Chang Gung Memorial Hospital, Taipei, Taiwan.
authors.forename: Chiz-Tzung
authors.initials: CT
authors.lastname: Chang
authors.forename: Cheng-Chieh
authors.initials: CC
authors.lastname: Hung
authors.forename: Ya-Chung
authors.initials: YC
authors.lastname: Tian
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Yang
authors.forename: Mai-Szu
authors.initials: MS
authors.lastname: Wu
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D057167:Claudins; D016572:Cyclosporine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D008138:Loop of Henle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D057167:Claudins; D007166:Immunosuppressive Agents; D008565:Membrane Proteins; D012333:RNA, Messenger; C502010:claudin 16; D016572:Cyclosporine; D008274:Magnesium