title: Non-lethal levels of oxidative stress in response to short-term intermittent hypoxia enhance ca²⁺ handling in neonatal rat cardiomyocytes.
abstract: OBJECTIVE
  Intermittent hypoxia (IH) may exert pre-conditioning-like cardioprotective effects and alter Ca(2+) regulation; however, the exact mechanism of these effects remains unclear. Thus, we examined Ca(2+)-handling mechanisms induced by IH in rat neonatal cardiomyocytes.
  
  
  METHODS
  Cardiomyocytes were exposed to repetitive hypoxia-re-oxygenation cycles for 1-4 days. Mitochondrial reactive oxygen species (ROS) generation was determined by flow cytometry, and intracellular Ca(2+) concentrations were measured using a live-cell fluorescence imaging system. Protein kinase C (PKC) isoforms and Ca(2+)-handling proteins were analysed using immunofluorescence and western blotting.
  
  
  RESULTS
  After IH exposure for 4 days, the rate of Ca(2+) extrusion from the cytosol to the extracellular milieu during 40-mM KCl-induced Ca(2+) mobilization increased significantly, whereas ROS levels increased mildly. IH activated PKC isoforms, which translocated to the membrane from the cytosol, and Na(+)/Ca(2+) exchanger-1, leading to enhanced Ca(2+) efflux capacity. Simultaneously, IH increased sarcoplasmic reticulum (SR) Ca(2+)-ATPase and ryanodine receptor 2 (RyR-2) activities and RyR-2 expression, resulting in improved Ca(2+) uptake and release capacity of SR in cardiomyocytes.
  
  
  CONCLUSIONS
  IH-induced mild elevations in ROS generation can enhance Ca(2+) efflux from the cytosol to the extracellular milieu and Ca(2+)-mediated SR regulation in cardiomyocytes, resulting in enhanced Ca(2+)-handling ability.
authors.affiliation: Center of Physical Education, Office of General and Basic Education, Tzu Chi University, Hualien, Taiwan.
authors.forename: Tsung-I
authors.initials: TI
authors.lastname: Chen
authors.forename: Yu-Cheng
authors.initials: YC
authors.lastname: Hsu
authors.forename: Chih-Feng
authors.initials: CF
authors.lastname: Lien
authors.forename: Jian-Hong
authors.initials: JH
authors.lastname: Lin
authors.forename: Hung-Wen
authors.initials: HW
authors.lastname: Chiu
authors.forename: Kun-Ta
authors.initials: KT
authors.lastname: Yang
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D015687:Cell Hypoxia; D002478:Cells, Cultured; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D018384:Oxidative Stress; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D017382:Reactive Oxygen Species; D002118:Calcium