Peroxynitrite Mediates Disruption of Ca 2+ Homeostasis by Carbon Monoxide via Ca 2+ ATPase Degradation

Abstract

Aim: Sublethal carbon monoxide poisoning causes prolonged neurological damage involving oxidative stress. Given the central role of Ca²⁺ homeostasis and its vulnerability to stress, we investigated whether CO disrupts neuronal Ca²⁺ homeostasis. Results: Cytosolic Ca²⁺ transients evoked by muscarine in SH-SY5Y cells were prolonged by CO (applied via the donor CORM-2), and capacitative Ca²⁺ entry (CCE) was dramatically enhanced. Ca²⁺ store mobilization by cyclopiazonic acid was similarly augmented, as was the subsequent CCE, and that evoked by thapsigargin. Ca²⁺ rises evoked by depolarization were also enhanced by CO, and Ca²⁺ levels often did not recover in its presence. CO increased intracellular nitric oxide (NO) and all effects of CO were prevented by inhibiting NO formation. However, NO donors did not mimic the effects of CO. The antioxidant ascorbic acid inhibited effects of CO on Ca²⁺ signaling, as did the peroxynitrite scavenger, FeTPPS, and CO increased peroxynitrite formation. Finally, CO caused significant loss of plasma membrane Ca²⁺ATPase (PMCA) protein, detected by Western blot, and this was also observed in brain tissue of rats exposed to CO in vivo. Innovation: The cellular basis of CO-induced neurotoxicity is currently unknown. Our findings provide the first data to suggest signaling pathways through which CO causes neurological damage, thereby opening up potential targets for therapeutic intervention. Conclusion: CO stimulates formation of NO and reactive oxygen species which, via peroxynitrite formation, inhibit Ca²⁺ extrusion via PMCA, leading to disruption of Ca²⁺ signaling. We propose this contributes to the neurological damage associated with CO toxicity. Antioxid. Redox Signal. 17, 744—755.