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

Abstract

Background and Purpose - Mitochondrial ATP-sensitive potassium (mitoKATP) channels are present in the brain, and several reports have shown that mitoKATP channel openers protect the brain against ischemic injury. However, the precise mechanisms of this protection are not well established. We hypothesized that mitoKATP channel openers prevent apoptosis by preserving mitochondrial membrane potential. Methods - We investigated the effect of mitoKATP channel openers on apoptosis induced by oxidative stress using cultured cerebellar granule neurons. Results - The mitoKATP 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 (ΔΨm) induced by H2O2. These effects were abolished by 5-hydroxydecanoate (500 μmol/L), a mitoKATP channel blocker. Cyclosporin A and bongkrekic acid, inhibitors of the mitochondrial permeability transition pore, also prevented ΔΨm 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 KATP channels. Conclusions - MitoKATP channel openers inhibited apoptosis by preserving mitochondrial inner membrane potential. These beneficial effects may suggest a possible new target for neuroprotection.