Abstract
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 Mg(2+) 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.