title: Exogenous nitric oxide triggers classic ischemic preconditioning by preventing intracellular Ca2+ overload in cardiomyocytes.
abstract: The involvement of nitric oxide (NO) in the late phase of ischemic preconditioning is well established. However, the role of NO as a trigger or mediator of "classic preconditioning" remains to be determined. The present study was designed to investigate the effects of NO on calcium homeostasis in cultured newborn rat cardiomyocytes in normoxia and hypoxia. We found that treatment with the NO donor, sodium nitroprusside (SNP) induced a sustained elevation of intracellular calcium level ([Ca(2+)](i)) followed by a decrease to control levels. Elevation of extracellular calcium, which generally occurs during ischemia, caused an immediate increase in [Ca(2+)](i) and arrhythmia in cultures of newborn cardiomyocytes. Treatment with SNP decreased [Ca(2+)](i) to control levels and re-established synchronized beating of cardiomyocytes. A decrease in extracellular [Na(+)], which inhibits the Na(+)/Ca(2+) exchanger, did not prevent [Ca(2+)](i) reduction by SNP. In contrast, application of thapsigargin, an inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a), increased [Ca(2+)](i), and in its presence, SNP did not reduce [Ca(2+)](i), indicating that Ca(2+) reduction is achieved via activation of SERCA2a. The results obtained suggest that activation of SERCA2a by SNP increases Ca(2+) uptake into the sarcoplasmic reticulum (SR) and prevents cytosolic Ca(2+) overload, which might explain the protective effect of SNP from hypoxic damage.
authors: Gonda (Goldschmied) Medical Diagnostic Research Center, The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors: Ophra
authors: O
authors: Rickover
authors: Tova
authors: T
authors: Zinman
authors: Doron
authors: D
authors: Kaplan
authors: Asher
authors: A
authors: Shainberg
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D006706:Homeostasis; D000860:Hypoxia; D019194:Ischemic Preconditioning; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000378:metabolism; D009599:Nitroprusside / Q000378:metabolism; D051381:Rats; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism
chemical_list: D020030:Nitric Oxide Donors; D009599:Nitroprusside; D009569:Nitric Oxide; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium