Selective role for superoxide in InsP(3) 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 Ca(2+) ([Ca(2+)](i)) transient in endothelial cells that was ablated by a combination of superoxide dismutase and an anion channel blocker. [Ca(2+)](i) store depletion, but not extracellular Ca(2+) chelation, prevented [Ca(2+)](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 [Ca(2+)](i) transient. Importantly, the O(2) (.−)-triggered Ca(2+) 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 [Ca(2+)](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.