Loss of the large conductance calcium-activated potassium channel causes an increase in mitochondrial reactive oxygen species in glioblastoma cells

Mitochondrial potassium (mitoK) channels play an important role in cellular physiology. These channels are expressed in healthy tissues and cancer cells. Activation of mitoK channels can protect neurons and cardiac tissue against injury induced by ischemia–reperfusion. In cancer cells, inhibition of mitoK channels leads to an increase in mitochondrial reactive oxygen species, which leads to cell death. In glioma cell activity of the mitochondrial, large conductance calcium-activated potassium (mitoBK(Ca)) channel is regulated by the mitochondrial respiratory chain. In our project, we used CRISPR/Cas9 technology in human glioblastoma U-87 MG cells to generate knockout cell lines lacking the α-subunit of the BK(Ca) channel encoded by the KCNMA1 gene, which also encodes cardiac mitoBK(Ca). Mitochondrial patch-clamp experiments showed the absence of an active mitoBK(Ca) channel in knockout cells. Additionally, the absence of this channel resulted in increased levels of mitochondrial reactive oxygen species. However, analysis of the mitochondrial respiration rate did not show significant changes in oxygen consumption in the cell lines lacking BK(Ca) channels compared to the wild-type U-87 MG cell line. These observations were reflected in the expression levels of selected mitochondrial genes, organization of the respiratory chain, and mitochondrial morphology, which did not show significant differences between the analyzed cell lines. In conclusion, we show that in U-87 MG cells, the pore-forming subunit of the mitoBK(Ca) channel is encoded by the KCNMA1 gene. Additionally, the presence of this channel is important for the regulation of reactive oxygen species levels in mitochondria.