A variety of direct and indirect techniques have revealed the existence of ATP-sensitive potassium (K(ATP)) channels in the inner membranes of mitochondria. The molecular identity of these mitochondrial K(ATP) (mitoK(ATP)) channels remains unclear. We used a pharmacological approach to distinguish mitoK(ATP) channels from classical, molecularly defined cardiac sarcolemmal K(ATP) (surfaceK(ATP)) channels encoded by the sulfonylurea receptor SUR2A and the pore-forming subunit K(ir)6.2. SUR2A and K(ir)6.2 were expressed in human embryonic kidney (HEK)293 cells, and their activities were measured by patch-clamp recordings of membrane current. SurfaceK(ATP) channels are activated potently by 100 μM pinacidil but only weakly by 100 μM diazoxide; in addition, they are blocked by 10 μM glibenclamide, but are insensitive to 500 μM 5-hydroxydecanoate. This pharmacology, which was confirmed with patch-clamp recordings in intact rabbit ventricular myocytes contrasts with that of mitoK(ATP) channels as indexed by flavoprotein oxidation. MitoK(ATP) channels in myocytes are activated equally by 100 μM diazoxide and 100 μM pinacidil. In contrast to its lack of effect on surfaceK(ATP) channels, 5-hydroxydecanoate is an effective blocker of mitoK(ATP) channels. Glibenclamide's effects on mitoK(ATP) channels are difficult to assess, because it independently activates flavoprotein fluorescence, consistent with a previously described primary uncoupling effect. Confocal imaging of the subcellular distribution of expressed fluorescent K(ir)6.2 in HEK cells and in myocytes revealed no targeting of mitochondrial membranes. The differences in drug sensitivity and subcellular localization indicate that mitoK(ATP) channels are distinct from surface N(ATP) channels at a molecular level.
ASJC Scopus subject areas
- Molecular Medicine