The effect of atp-dependent potassium uptake on mitochondrial functions under acute hypoxia

Diazoxide Needs Mitochondrial Connexin43 to Exert Its Cytoprotective Effect in a Cellular Model of CoCl2-Induced Hypoxia

Hypoxia is the leading cause of death in cardiomyocytes. Cells respond to oxygen deprivation by activating cytoprotective programs, such as mitochondrial connexin43 (mCx43) overexpression and the opening of mitochondrial K_ATP channels, aimed to reduce mitochondrial dysfunction. In this study we used an in vitro model of CoCl₂-induced hypoxia to demonstrate that mCx43 and K_ATP channels cooperate to induce cytoprotection. CoCl₂ administration induces apoptosis in H9c2 cells by increasing mitochondrial ROS production, intracellular and mitochondrial calcium overload and by inducing mitochondrial membrane depolarization. Diazoxide, an opener of K_ATP channels, reduces all these deleterious effects of CoCl₂ only in the presence of mCx43. In fact, our results demonstrate that in the presence of radicicol, an inhibitor of Cx43 translocation to mitochondria, the cytoprotective effects of diazoxide disappear. In conclusion, these data confirm that there exists a close functional link between mCx43 and K_ATP channels.

Inhibition of ATP-sensitive potassium channels exacerbates anoxic coma in Locusta migratoria

We demonstrate the involvement of ATP-sensitive K+ (KATP) channels during recovery from spreading depolarization (SD) induced via anoxic coma in locusts. KATP inhibition using glybenclamide impaired ion homeostasis across the blood-brain barrier, resulting in a longer time to recovery of transperineurial potential following SD. Comparison with ouabain indicates that the effects of glybenclamide are not mediated by the Na+/K+-ATPase but are a result of KATP channel inhibition.

Diazoxide affects mitochondrial bioenergetics by the opening of mKATP channel on submicromolar scale

Background

Cytoprotection afforded by mitochondrial ATP-sensitive K⁺-channel (mK_ATP-channel) opener diazoxide (DZ) largely depends on the activation of potassium cycle with eventual modulation of mitochondrial functions and ROS production. However, generally these effects were studied in the presence of Mg∙ATP known to block K⁺ transport. Thus, the purpose of our work was the estimation of DZ effects on K⁺ transport, K⁺ cycle and ROS production in rat liver mitochondria in the absence of Mg∙ATP.

Results

Without Mg·ATP, full activation of native mK_ATP-channel, accompanied by the increase in ATP-insensitive K⁺ uptake, activation of K⁺-cycle and respiratory uncoupling, was reached at ≤0.5 μM of DZ,. Higher diazoxide concentrations augmented ATP-insensitive K⁺ uptake, but not mK_ATP-channel activity. mK_ATP-channel was blocked by Mg·ATP, reactivated by DZ, and repeatedly blocked by mK_ATP-channel blockers glibenclamide and 5-hydroxydecanoate, whereas ATP-insensitive potassium transport was blocked by Mg²⁺ and was not restored by DZ. High sensitivity of potassium transport to DZ in native mitochondria resulted in suppression of mitochondrial ROS production caused by the activation of K⁺-cycle on sub-micromolar scale. Based on the oxygen consumption study, the share of mK_ATP-channel in respiratory uncoupling by DZ was found.

Conclusions

The study of mK_ATP-channel activation by diazoxide in the absence of MgATP discloses novel, not described earlier, aspects of mK_ATP-channel interaction with this drug. High sensitivity of mK_ATP-channel to DZ results in the modulation of mitochondrial functions and ROS production by DZ on sub-micromolar concentration scale. Our experiments led us to the hypothesis that under the conditions marked by ATP deficiency affinity of mK_ATP-channel to DZ can increase, which might contribute to the high effectiveness of this drug in cardio- and neuroprotection.