Persistent mitoK_ATP Activation Is Involved in the Isoflurane-induced Cytotoxicity

Isoflurane exposure induces apoptosis in cultured cells and in the developing brain, while the underlying mechanism remains largely unclarified. This study was designed to determine whether the disruption of mitoK_ATP-mediated ATP balance was involved in the cytotoxicity of isoflurane. Human neuroglioma cells U251 and 7-day-old mice were treated with isoflurane. A specific mitoK_ATP antagonist 5-HD was used, and the cellular ATP levels, NAD⁺/NADH ratios, and mitochondrial transmembrane potential (ΔΨ_m) were measured. Our data showed that the blockage of mitoK_ATP by 5-HD mitigated the isoflurane-induced ΔΨ_m disruption, reactive oxygen species (ROS) accumulation, and apoptosis in U251 cells. Moreover, we found that the toxic effect of isoflurane was not observed in the first 2-h exposure; instead, the cellular ATP levels and NAD⁺/NADH ratios were markedly increased. The reduction of ATP levels and NAD⁺/NADH ratios was only detected after this initial phase. This dynamical effect of isoflurane was blocked by 5-HD. In contrast, a ROS scavenger NAC sustained the isoflurane-induced ATP elevation. Similar results were observed in animal studies. And again, 5-HD attenuated isoflurane-induced cognitive disorders in the Intellicage test, a system that assesses place learning behavior in a social environment. Our study uncovered a potential mechanism underlying isoflurane's toxicity with a therapeutic future.