Mitochondrial ATP-sensitive potassium channel activation protects cerebellar granule neurons from apoptosis induced by oxidative stress

Background and Purpose - Mitochondrial ATP-sensitive potassium (mitoK_ATP) channels are present in the brain, and several reports have shown that mitoK_ATP channel openers protect the brain against ischemic injury. However, the precise mechanisms of this protection are not well established. We hypothesized that mitoK_ATP channel openers prevent apoptosis by preserving mitochondrial membrane potential. Methods - We investigated the effect of mitoK_ATP channel openers on apoptosis induced by oxidative stress using cultured cerebellar granule neurons. Results - The mitoK_ATP channel opener diazoxide (100 μmol/L) significantly suppressed the number of cells with terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive nuclei and the increase in caspase-3 activity induced by 20 μmol/L H₂O₂. Diazoxide and another opener, pinacidil, prevented the loss of mitochondrial inner membrane potential (ΔΨ_m) induced by H₂O₂. These effects were abolished by 5-hydroxydecanoate (500 μmol/L), a mitoK_ATP channel blocker. Cyclosporin A and bongkrekic acid, inhibitors of the mitochondrial permeability transition pore, also prevented ΔΨ_m loss, confirming the involvement of the mitochondrial permeability transition in the apoptotic cascade in neurons. Furthermore, diazoxide prevented the increase in extracellular glutamate concentration induced by H₂O₂, but this effect was not attributable to activation of surface K_ATP channels. Conclusions - MitoK_ATP channel openers inhibited apoptosis by preserving mitochondrial inner membrane potential. These beneficial effects may suggest a possible new target for neuroprotection.