An inhibitor of potassium mitochondrial channels quinidine (0.1 mM) closed the ATP-sensitive potassium channels isolated from mitochondria and reconstituted into a bilayer lipid membrane. Inhibitors of cytoplasm membrane K-channels (ouabain, tetraethyl ammonium, and cesium ions) produced no effect on the ATP-sensitive mitochondria K-channels; 0.5-2 microM glybenclamide did not affect the reconstituted channels, either. The multiplicity of jumps of conductivity at small concentration of the protein and the maintenance of ion selectivity at switching various levels of conductivity lead us to assume that the large channels are clusters of elementary channels. The average frequency of channel-cluster switchovers between various levels of conductivity is much higher than at the elementary channel.