Targeting Mitochondrial Large-Conductance Calcium-Activated Potassium Channel by Hydrogen Sulfide via Heme-Binding...

Reperfusion together with the preceding ischemic period results in serious damage to brain and heart tissues. Activation of potassium channels from the inner mitochondrial membrane leads to cytoprotection during such events. The mitochondrial large-conductance calcium-activated potassium channel (mitoBK_Ca) is one of these cytoprotective channels. It was previously shown that BK_Ca channels are blocked by hemin, which is present in excess during hemorrhage. In the experiments described in this work, we checked whether NaHS, known as a donor of gasotransmitter hydrogen sulfide (H₂S), which can play an important role in cytoprotection, interacts with mitoBK_Ca channels. Indeed, using the biotin-switch method, it was found that mitoBK_Ca channels undergo S-sulfhydration in the presence of NaHS. Although patch-clamp experiments showed that NaHS has negligible effects on the activity of mitoBK_Ca channels, NaHS has been shown to almost fully activate hemin-inhibited mitoBK_Ca channels. The effects of NaHS were mimicked by imidazole, suggesting a common mechanism of activation of mitoBK_Ca channels inhibited by heme/hemin by molecules able to coordinate the iron ion of porphyrin. A set of absorption spectroscopy experiments with the 23 amino acid model peptides containing the heme-binding motif CXXCH suggested previously unrecognized roles of cysteines in heme binding. SIGNIFICANCE STATEMENT: The activity of mitochondrial channels including mitoBK_Ca seems to play a significant role in cytoprotection during ischemia/reperfusion. Hemin, which is present in excess during hemorrhage, can potentially bind to and inhibit mitoBK_Ca activity. We found that hydrogen sulfide does not affect mitoBK_Ca activity unless it is blocked by hemin. In this case, hydrogen sulfide activates hemin-inhibited mitoBK_Ca by binding to hemin iron. The hydrogen sulfide effect could be mimicked in patch-clamp experiments by imidazole probably acting by a similar mechanism.