Single channel properties of mitochondrial large conductance potassium channel formed by BK-VEDEC splice variant

The activation of mitochondrial large conductance calcium-activated potassium (mitoBK_Ca) channels increases cell survival during ischemia/reperfusion injury of cardiac cells. The basic biophysical and pharmacological properties of mitoBK_Ca correspond to the properties of the BK_Ca channels from the plasma membrane. It has been suggested that the VEDEC splice variant of the KCNMA1 gene product encoding plasma membrane BK_Ca is targeted toward mitochondria. However there has been no direct evidence that this protein forms a functional channel in mitochondria. In our study, we used HEK293T cells to express the VEDEC splice variant and observed channel activity in mitochondria using the mitoplast patch-clamp technique. For the first time, we found that transient expression with the VEDEC isoform resulted in channel activity with the conductance of 290 ± 3 pS. The channel was voltage-dependent and activated by calcium ions. Moreover, the activity of the channel was stimulated by the potassium channel opener NS11021 and inhibited by hemin and paxilline, which are known BK_Ca channel blockers. Immunofluorescence experiments confirmed the partial colocalization of the channel within the mitochondria. From these results, we conclude that the VEDEC isoform of the BK_Ca channel forms a functional channel in the inner mitochondrial membrane. Additionally, our data show that HEK293T cells are a promising experimental model for expression and electrophysiological studies of mitochondrial potassium channels.