Selective role for superoxide in InsP3 receptor-mediated mitochondrial dysfunction and endothelial apoptosis

Reactive oxygen species (ROS) play a divergent role in both cell survival and cell death during ischemia/reperfusion (I/R) injury and associated inflammation. In this study, ROS generation by activated macrophages evoked an intracellular Ca2+ ([Ca2+](i)) transient in endothelial cells that was ablated by a combination of superoxide dismutase and an anion channel blocker. [Ca2+](i) store depletion, but not extracellular Ca2+ chelation, prevented [Ca2+](i) elevation in response to O-2(.-) that was inositol 1,4,5- trisphosphate (InsP(3)) dependent, and cells lacking the three InsP(3) receptor (InsP(3)R) isoforms failed to display the [Ca2+](i) transient. Importantly, the O-2(.-)-triggered Ca2+ mobilization preceded a loss in mitochondrial membrane potential that was independent of other oxidants and mitochondrially derived ROS. Activation of apoptosis occurred selectively in response to O-2(.-) and could be prevented by [Ca2+](i) buffering. This study provides evidence that O-2(.-) facilitates an InsP(3)R-linked apoptotic cascade and may serve a critical function in I/R injury and inflammation.