Diazoxide-induced cardioprotection via ΔΨm loss depending on timing of application

Abstract

Although the role of mitochondrial ATP-sensitive potassium (mitoK ATP) channels in cardioprotection is widely accepted, it remains unclear when their opening is critical for protection. We tested the hypothesis that the mitoK ATP channel acts as a trigger or mediator of protection against apoptosis through loss of mitochondrial inner membrane potential (ΔΨm). Exposure of neonatal rat cardiomyocytes to H 2O 2 (0.5 mmol/L) resulted in apoptosis associated with severe ΔΨm loss. Pretreatment with diazoxide (20 to 100 μmol/L) prevented H 2O 2-induced apoptosis and ΔΨm loss at 2 but not 18 h after exposure, while the latter was prevented by cotreatment with diazoxide. Lack of protection by pretreatment with diazoxide was observed in cardiomyocytes cultured in a medium containing H 2O 2 for 2 h and then not containing for 16 h. The slopes of the regression lines of the relationship between the proportion of apoptotic cells and ΔΨm loss ( y = − 0.89 vs. − 0.42) and the proportion of cells with high side scatter signal differed between cardiomyocytes exposed H 2O 2 for 2 and 18 h. Diazoxide per se caused a transient ΔΨm loss (within 30 min) with a recovery followed by persistent ΔΨm loss (after 6 h). Inhibition of the former by 5-hydroxydecanoate (5-HD, 0.5 mmol/L) abolished protection of pretreatment with diazoxide (trigger phase), while that of the latter prevented the protection of cotreatment with diazoxide (mediator phase). Our results suggest that mitoK ATP channels act as a trigger and mediator of cardioprotection through a transient or persistent ΔΨm loss depending on phenotypic consequence in response to oxidants.