Flavonoid quercetin abolish paxilline inhibition of the mitochondrial BKCa channel.

• Quercetin potently activates the mitoBK Ca channel, and this effect is not inhibited by the canonical blocker of this channel, paxilline. • Analog of quercetin, isorhamnetin, has no effect on the mitoBK Ca channel activity. • Due to steric hindrance, the quercetin is large enough to block paxilline from reaching its binding site. Large-conductance calcium-regulated potassium channel (BK Ca) is known to play an important role in physiological and pathological processes. Despite the BK Ca channel being encoded by one gene, this channel has been found to be located not only in the cell membrane but also in the membranes of intracellular compartments, such as in the inner mitochondrial membrane. With some differences, the mitochondrial BK Ca (mitoBK Ca) channel has been shown to be activated or inhibited by both synthetic and natural compounds. One of them, paxilline, has been considered to be a canonical blocker of this channel. In the previous study, we showed that the natural origin substance quercetin activates the mitoBK Ca channel at ten times lower the concentration compared to channel present in the plasma membrane. Here, using the patch-clamp technique, we report that after inhibition of mitoBK Ca channels by paxilline, quercetin activates these channels, indicating a paxilline and quercetin binding competition in the regulation of the mitoBK Ca channel. To support our hypothesis, we used an analog of quercetin – isorhamnetin, a substance with one substituent changed. Isorhamnetin has no effect on the mitoBK Ca channel activity, and after its application, paxilline fully inhibits the channel. Additionally, the molecular modeling studies were used. The results of docking quercetin and paxilline to the BK Ca channel suggest that paxilline cannot bind after activation of the channel with quercetin. It seems that the likely mechanism of this phenomenon is the formation of spatial hindrance by quercetin. The results obtained shed a completely new, groundbreaking in the paxilline context, light on the current knowledge about mitochondrial potassium channel regulation. [ABSTRACT FROM AUTHOR]