Comparison of hypoxic effects induced by chemical and physical hypoxia on cardiomyocytes.

The degree and duration of chemical hypoxia induced by sodium dithionite (NaSO) have not been reported. It is not yet clear how much reduction in the O concentration (physical hypoxia) can lead to hypoxia in cultured cardiomyocytes. In this study, oxygen microelectrodes were used to measure changes in the O concentration in media containing different concentrations of NaSO. Then, hypoxic effects of 0.8, 1.0, and 2.0 mM NaSO or 1%, 3%, and 5% O in cultured cardiomyocytes from neonatal rats were observed and compared. The results showed that the O concentration failed to remain constant by NaSO treatment during the 180-minute observation period. Only the 2.0 mM NaSO group significantly increased the expression of hypoxia-inducible factor 1α (HIF-1α) and hypoxic responses. Notably, 3% O only significantly increased the expression of HIF-1α in cardiomyocytes, while 1% O not only increased the expression of HIF-1α but also increased the apoptotic rate in cardiomyocytes. These results suggest that NaSO is not suitable for establishing a hypoxic model in cultured neonatal rat cardiomyocytes, and neonatal rat cardiomyocytes cultured at or below 1% O induced significant hypoxic effects, which can be used as a starting O concentration for establishing a hypoxic cell model.