title: Characteristics of spontaneous calcium oscillations in renal tubular epithelial cells.
abstract: BACKGROUND
  The kidney is a major organ involved in calcium (Ca(2+)) metabolism. Ca(2+) is transported through renal tubular epithelial cells. The intracellular free calcium concentration ([Ca(2+)](i)) is tightly controlled at a low concentration, but transient increases and oscillations in [Ca(2+)](i) are induced by various conditions. In this study, we investigated the mechanisms underlying the spontaneous [Ca(2+)](i) oscillations observed in MDCK cells.
  
  
  METHODS
  [Ca(2+)](i) was monitored in fura-2-loaded Madin-Darby canine kidney (MDCK) cells using a calcium imaging system. We investigated the mechanism by which [Ca(2+)](i) changed by applying drugs or by changing the extracellular Ca(2+) concentration.
  
  
  RESULTS
  Spontaneous [Ca(2+)](i) oscillations occurred in MDCK cells. The oscillations occurred irregularly and were not transmitted to neighboring cells. Spontaneous [Ca(2+)](i) oscillations in MDCK cells were initiated by Ca(2+) release from ryanodine/IP(3)-sensitive intracellular calcium stores, and their frequency was largely unaffected by the extracellular Ca(2+) concentration. Moreover, the frequency of the oscillations was increased by extracellular nucleotide, but was decreased when the nucleotides were removed.
  
  
  CONCLUSIONS
  Our study suggested that [Ca(2+)](i) release from ryanodine/IP(3)-sensitive intracellular calcium stores mediates spontaneous [Ca(2+)](i) oscillations in MDCK cells. Calcium oscillations may be associated with the function of the renal tubular epithelial cells.
authors.affiliation: Division of Kidney and Hypertension, Department of Internal Medicine, The Jikei University School of Medicine, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Udagawa
authors.forename: Kazushige
authors.initials: K
authors.lastname: Hanaoka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kawamura
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Hosoya
mesh_terms: D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002460:Cell Line; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D004963:Estrenes / Q000494:pharmacology; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007684:Kidney Tubules / Q000378:metabolism*; D011339:Probenecid / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology
chemical_list: D001896:Boron Compounds; D004963:Estrenes; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D012433:Ryanodine; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; C109986:2-aminoethoxydiphenyl borate; D011339:Probenecid; D002118:Calcium; D016257:Fura-2