Mitochondria present in excised patches from pancreatic B-cells may form microcompartments with ATP-dependent potassium channels

Experiments with inside-out patches excised from pancreatic B-cells have yi elded evidence that mitochondria are often contained in the cytoplasmic plu g protruding into the tip of patch pipette. When intact B-cells were loaded with the fluorescent mitochondrial stain, rhodamine 123, and membrane patc hes excised from these cells, a green fluorescence could be observed in the lumen at the tip of the patch pipette. The same result was obtained with t he mitochondrial stain, MitoTracker Green FM, which is only fluorescent in a membrane-bound state. Furthermore, the open probability of ATP-dependent potassium (K-ATP) channels in inside-out patches was influenced by mitochon drial fuels and inhibitors. Respiratory substrates like tetramethyl phenyle ne diamine (2 mM) plus ascorbate (5 mM) or alpha-ketoisocaproic acid (10 mM ) reduced the open probability of K-ATP channels in inside-out patches sign ificantly (down to 57% or 65% of control, respectively). This effect was an tagonized by the inhibitor of cytochrome oxidase, sodium azide (5 mM). Like wise, the inhibitor of succinate dehydrogenase, malonate (5 mM), increased the open probability of K-ATP channels in the presence of succinate (1 mM). However, oligomycin in combination with antimycin and rotenone did not inc rease open probability. Although it cannot be excluded that these effects r esult from a direct interaction with the K-ATP channels, the presence of mi tochondria in the close vicinity permits the hypothesis that changes in mit ochondrial metabolism are involved, mitochondria and K-ATP channels thus fo rming functional microcompartments.