Endothelin-1 Aggravates Hypoxia/Reoxygenationinduced Injury in Renal Epithelial Cells through the Activation of a Na+/Ca2+ Exchanger

Abstract

We analyzed the role of the Na/Ca2+ exchanger (NCX) in hypoxia/reoxygenation-induced injury and also its interaction with endothelin-1 in the proximal epithelial cell line LLC-PK1. The hypoxia/reoxygenation protocol caused a significant leakage of lactate dehydrogenase from parental LLC-PK1 cells, which was markedly suppressed by KB-R7943, a selective NCX inhibitor. Overexpression of wild-type NCX1 into LLC-PK1 cells enhanced the release of lactate dehydrogenase and produced more severe morphological changes, such as bleb formation, during reoxygenation. Endothelin-1 significantly aggravated hypoxia/reoxygenation- induced injuries in parental and NCX1-overexpressing LLC-PK1 cells. Such aggravation by endothelin-1 was not observed in cells overexpressing a deregulated NCX1 mutant, which displays no protein kinase C-dependent activation. KB-R7943 suppressed those cell injuries aggravated by endothelin-1, but not those in cells overexpressing a KB-R7943-insensitive NCX1 mutant. We confirmed that these cell injuries were relevant to their cellular Ca accumulations induced by hypoxia/reoxygenation. These results suggest that Ca2+ overload via NCX plays a critical role in hypoxia/reoxygenation-induced renal tubular injury, and that endothelin-1 aggravates the cell damage through the activation of NCX.