The mitochondrial K(ATP) channel opener BMS-191095 induces neuronal preconditioning

Effects of ATP-sensitive potassium channel activators diazoxide and BMS-191095 on membrane potential and reactive oxygen species production in isolated piglet mitochondria

Mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel openers protect the piglet brain against ischemic stress. Effects of mitoK(ATP) channel agonists on isolated mitochondria, however, have not been directly examined. We investigated the effects of K(ATP) channel openers and blockers on membrane potential and on the production of reactive oxygen species (ROS) in isolated piglet mitochondria. Diazoxide and BMS-191095, putative selective openers of mitoK(ATP), decreased the mitochondrial membrane potential (delta psi(m)). On a molar basis, diazoxide was less effective than BMS-191095. In contrast, diazoxide but not BMS-191095 increased ROS production by mitochondria. Since diazoxide also inhibits succinate dehydrogenase (SDH), we examined the effects of 3-nitropropionic acid (3-NPA), an inhibitor of SDH. 3-NPA failed to change the delta psi(m) but increased ROS production. Inhibitors of K(ATP) channels did not affect resting delta psi(m) or ROS production, but glibenclamide and 5-hydroxydecanoate (5-HD) blocked effects of diazoxide and BMS-191095 on delta psi(m) and diazoxide effects on ROS production. We conclude that BMS-191095 has selective effects on mitoK(ATP) channels while diazoxide also increases ROS production probably via inhibition of SDH.

Targeting mitochondrial ATP-sensitive potassium channels--a novel approach to neuroprotection

Mitochondrial responses to ischemic stress play an important role in necrosis and apoptosis of brain cells. Recent studies using several different experimental preparations have shown that activation of ATP-sensitive potassium channels in mitochondria (mitoK(ATP) channels) is able to protect neurons and astroglia against injury and death. Thus, targeting of mitoK(ATP) channels appears to be a novel approach to neuroprotection. However, little is known about the mechanisms involved. The purpose of this review is to detail the current state of knowledge about this important, emerging area of investigation, and to provide suggestions for future studies.

Diazoxide preconditioning protects against neuronal cell death by attenuation of oxidative stress upon glutamate stimulation

We examined the effects of diazoxide, the putative mitochondrial adenosine triphosphate-sensitive potassium (mitoK(ATP)) channel opener, against glutamate excitotoxicity in primary cultures of rat cortical neurons. Cells were treated with diazoxide for 24 hr and then exposed to 200 microM glutamate. Cell viability was measured 24 hr after glutamate exposure. We found that treatment 24 hr before glutamate exposure with 250 and 500 microM diazoxide but not with another mitoK(ATP) channel opener, nicorandil, increased neuronal viability from 54 +/- 2% to 84 +/- 2% and 92 +/- 3%, respectively (n = 25-40). These effects were not inhibited by the putative mitoK(ATP) channel blocker 5-hydroxydecanoic acid. Diazoxide application increased production of reactive oxygen species (ROS) and coapplication of M40401, a superoxide dismutase mimetic, prevented delayed preconditioning. The 24 hr preconditioned neurons showed significantly reduced ROS production upon glutamate stimulation compared to that in untreated cells. These results suggest that diazoxide induces delayed preconditioning in cultured cortical neurons via increased ROS production and attenuation of oxidative stress upon glutamate stimulation.