In vitro activity: Nicorandil (100 mM) increases Flavoprotein oxidation but not membrane current; a 10-fold higher concentration recruits both mitoK(ATP) and surfaceK(ATP) channels. Nicorandil bluntes the rate of cell death in a pelleting model of ischemia; this cardioprotective effect is prevented by the mitoK(ATP) channel blocker 5-hydroxydecanoate but is unaffected by the surfaceK(ATP) channel blocker HMR1098. Nicorandil (100 mM) suppresses TUNEL positivity, cytochrome c translocation, caspase-3 activation and dissipation of mitochondrialinner membrane potential (Delta(Psi)(m)). Nicorandil prevents Delta(Psi)(m) depolarization in a concentration-dependent manner (EC(50) approximately 40 mM, with saturation by 100 mM), as shown by fluorescence-activated cell sorter analysis of cells stained with a fluorescent Delta(Psi)(m)-indicator, tetramethylrhodamine ethyl ester (TMRE). Nicorandil activates a weakly inwardly-rectifying, glibenclamide-sensitive 80 pS K+ channel in both the transfected cells. Nicorandil preferentially activates the K(ATP) channels containing SUR2B in HEK293T cells. Nicorandil (100 mM) significantly suppresses the number of cells with TUNEL-positive nuclei and the increase in caspase-3 activity induced by 20 mM H2O2. Nicorandil prevents the loss of DeltaPsim induced by H2O2 in a concentration-dependent manner.