Non-Lethal levels of oxidative stress in response to short-term intermittent hypoxia enhance Ca handling in neonatal rat cardiomyocytes

Abstract

Background/Aims: 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. Copyright © 2014 S. Karger AG, Basel.