title: Hypoxia-induced cytosolic calcium influx is mediated primarily by the reverse mode of Na+/Ca2+ exchanger in smooth muscle cells of fetal small pulmonary arteries.
abstract: OBJECTIVE
  Constriction of small pulmonary arteries and high resistance of pulmonary circulation are important for maintaining fetal circulation before birth. In this study, we investigated how cytosolic free calcium concentration ([Ca(2+)]i) in fetal lamb small pulmonary artery smooth muscle cells (SPASMC) was affected by hypoxia and regulated by calcium pumps during this process.
  
  
  METHODS
  (Ca(2+))i in response to acute hypoxia was determined spectrofluorometrically with fluo-3AM in cultured fetal SPASMC. Chemicals or solutions, including ryanodine, 2-aminoethoxydiphenyl borate, Ca(2+)-free solution with 20 mmol ethyleneglycoltetraacetic (EGTA), nimodipine, Na(+)-free medium and KB-R7943, were administrated at the same time point when samples were exposed to acute hypoxia.
  
  
  RESULTS
  (Ca(2+))i in fetal lamb SPASMC increased under acute hypoxia. 2-Aminoethoxydiphenyl borate, an inhibitor of inositol triphosphate calcium store, partially attenuated the (Ca(2+))i increase after 6-min treatment. Ryanodine, an inhibitor of ryanodine-sensitive calcium stores, had no effect on the (Ca(2+))i increase. Ca(2+)-free solution with EGTA completely abolished this increase. Both nimodipine, that blocks the voltage-gated calcium channel, and KB-R7943, that inhibits the reverse mode of Na(+)/Ca(2+) exchanger, greatly diminished the hypoxia-induced (Ca(2+))i increase. The inhibitory effect of KB-R7943 was stronger than nimodipine, evidenced by the fact that (Ca(2+))i dropped near to the baseline level in the presence of KB-R7943 at a later time point. Low extracellular Na(+) concentration enhanced the hypoxia-induced increase of (Ca(2+))i.
  
  
  CONCLUSIONS
  These results suggest that hypoxia-induced Ca(2+) increase in fetal SPASMC results from cytosolic Ca(2+) influx mediated primarily by the reverse mode of Na(+)/Ca(2+) exchanger.
authors.affiliation: Department of Cardiac and Thoracic Surgery, Shanghai Children's Medical Center, Shanghai Jiaotong University School of Medicine and Shanghai Pediatric Congenital Heart Disease Institute, Shanghai, China.
authors.forename: Yanjuan
authors.initials: Y
authors.lastname: Sun
authors.forename: Lincai
authors.initials: L
authors.lastname: Ye
authors.forename: Jinfen
authors.initials: J
authors.lastname: Liu
authors.forename: Haifa
authors.initials: H
authors.lastname: Hong
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005333:Fetus / Q000502:physiology; D000860:Hypoxia / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D011651:Pulmonary Artery / Q000196:embryology / Q000378:metabolism*; D011652:Pulmonary Circulation; D012756:Sheep; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D014661:Vasoconstriction
chemical_list: D015220:Calcium Channels; D019831:Sodium-Calcium Exchanger; D002118:Calcium
keywords: calcium pump; fetus; hypoxia; pulmonary artery; sodium/calcium exchanger