Roles of NHE1 and iPLA2 in ischemia/reperfusion‐induced damage in HL‐1 mouse cardiomyocytes

The Na + /H + exchanger, NHE1, and the Ca 2+ ‐independent phospholipase A 2 (iPLA 2 ) play complex roles in modulation of cell death. Here, we address the roles of NHE1 and iPLA 2 , specifically iPLA 2 β in simulated ischemia/reperfusion (I/R) (0.5% O 2 , 5 h, reperfusion 4‐8 h) in HL‐1 cardiomyocytes. I/R elicited mitochondrial fragmentation, F‐actin degradation, and cell death by necrosis and other non‐caspase pathways. Cell viability after I/R was greater at pH o 6.0 than at pH o 7.4. The NHE1 inhibitor EIPA decreased cell viability and increased necrosis during normoxia and in I/R pH o 6.0. The iPLA 2 inhibitor bromoenol‐lactone (BEL) substantially decreased viability and increased necrosis during normoxia and, to a lesser extent, in I/R. BEL treatment alone elicited F‐actin degradation in normoxia. NHE1 expression was reduced by 40 and 50% at the mRNA and protein level, respectively, by hypoxia, followed by an increase in mRNA level above control value during reperfusion at pH o 6.0. A comparable, yet less pronounced pattern was observed for iPLA 2 β. Finally, I/R elicited translocation of iPLA 2 β to the nuclear region. In conclusion, NHE1 and iPLA 2 exert net pro‐survival effects under normoxia and in simulated I/R in HL‐1 cardiomyocytes, in part by counteracting necrotic cell death. This effect of iPLA 2 is reduced by I/R, either due to iPLA 2 downregulation or because of an additional, I/R‐ associated detrimental effect of iPLA 2 activity.