KIR6.1 - A POSSIBLE SUBUNIT OF ATP-SENSITIVE K+ CHANNELS IN MITOCHONDRIA

We have investigated the subcellular localization of the inwardly rect ifying K+ channel subunit Kir6.1 (uK(ATP)-1). Immunoblot analysis of t he mitochondrial fractions prepared from rat skeletal muscle and liver detected a single band of Kir6.1 at 51 kDa, the intensity of which wa s stronger than that found in the total homogenate of each tissue. By immunofluorescence staining, the labelling for Kir6.1 was observed as a dispersed array of fine dots throughout all the tissues examined in the rat, including skeletal muscle, cardiac muscle, liver, and pancrea s. Electron-microscopic examination revealed that the punctate stainin g distribution was due to a specific labelling of Kir6.1 in the mitoch ondria. Immune-positive colloidal gold particles were scattered over t he mitochondria, suggesting that Kir6.1 was located on the inner membr ane. Although gold particles were not observed at plasma membrane, a 4 7kDa protein was detected in the isolated plasma membrane vesicles by immunoblot analysis against Kir6.1. These results suggest that Kir6.1 might be a subunit of the ATP-sensitive K+ channel in the mitochondrio n, as well as in the plasma membrane. (C) 1997 Academic Press.