Ion channels selective for potassium ions are present in the inner mitochondrial membranes. The mitochondrial ATP regulated potassium channel (mitoK_ATP channel) was identified by patch–clamp recordings in the inner membrane of liver mitochondria. Later, a similar channel was described in heart, brain and skeletal muscle mitochondria. Similarly to the plasma membrane K_ATP channel, the mitochondrial channel is inhibited by antidiabetic sulfonylureas and activated by potassium channel openers such as diazoxide or nicorandil. However, molecular properties and regulation by endogenous effectors of the mitoK_ATP channel remain unclear.

In our study, inner mitochondrial membranes from bovine heart were reconstituted using planar lipid bilayer technique. After incorporation, a potassium selective current was observed. The mean conductance was about 103 pS in symmetrical 150/150 mM KCl (cis/trans) solution. The effects of different K_ATP channel modulators on single channel activity were examined. The channel activity was inhibited by ATP/Mg²⁺ complex and 5-hydroxydecanoic acid. After ATP/Mg²⁺ inhibition activity of the channel was reversed upon BMS191095 application. Apart from this, inhibitors of a mitochondrial Ca²⁺ activated, large conductance potassium channel (mitoBK_Ca channel) – iberiotoxin and charybdotoxin had no effect on channel activity.

In further experiments the effects of pH on mitoK_ATP channel activity were studied. During trans side alkalization an increase in the current amplitude and opening probability was observed. The effect was reversed after perfusion. The cis side was not sensitive for alkalization. On the other hand, we observed that acidification of the cis side decreased opening probability of the channel. This effect was reversed by perfusion with neutral pH medium.

Next, the effects of different nucleotides on single channel activity were examined. The channel activity was inhibited by ATP/Mg²⁺ complex and activated by GDP or GTP. Detailed analysis of regulation of the mitoK_ATP channel by ATP-PNP/Mg²⁺ complex was performed. We did not observe inhibition of the mitoK_ATP channel activity by non-hydrolysable ATP analogues. Additionally we observed “run down” of the mitoK_ATP channel activity. Re-activation of the mitoK_ATP channel was observed upon transient/perfusion with ATP/Mg²⁺ complex. We conclude that ATP/Mg²⁺ complex regulate activity of the cardiac mitoK_ATP channel probably by phosphorylation reaction.

This work was supported by grant No. N301 053 31/1676 and Polish Mitochondrial Network MitoNet.pl .

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