Reduced SERCA activity underlies dysregulation of Ca(2+) homeostasis under atmospheric O(2) levels

Unregulated increases in cellular Ca(2+) homeostasis are a hallmark of pathophysiological conditions and a key trigger of cell death. Endothelial cells cultured under physiologic O(2) conditions (5% O(2)) exhibit a reduced cytosolic Ca(2+) response to stimulation. The mechanism for reduced plateau [Ca(2+)](i) upon stimulation was due to increased sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA)-mediated reuptake rather than changes in Ca(2+) influx capacity. Agonist-stimulated phosphorylation of the SERCA regulatory protein phospholamban was increased in cells cultured under 5% O(2). Elevation of cytosolic and mitochondrial [Ca(2+)] and cell death after prolonged ionomycin treatment, as a model of Ca(2+) overload, were lower when cells were cultured long-term under 5% compared with 18% O(2). This protection was abolished by cotreatment with the SERCA inhibitor cyclopiazonic acid. Taken together, these results demonstrate that culturing cells under hyperoxic conditions reduces their ability to efficiently regulate [Ca(2+)](i), resulting in greater sensitivity to cytotoxic stimuli.—Keeley, T. P., Siow, R. C. M., Jacob, R., Mann, G. E. Reduced SERCA activity underlies dysregulation of Ca(2+) homeostasis under atmospheric O(2) levels.