|Budget Amount *help
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 1996: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1995: ¥1,900,000 (Direct Cost: ¥1,900,000)
In pancreatic beta-cells, ATP-sensitive potassium channels (K_<ATP> channels) are crucial for the regulation of glucoseinduced insulin secretion and are the target for the sulfonylureas, oral hypoglycemic agents widely used in the treatment of non-insulin-dependent diabetes mellitus (NIDDM), but the molecular basis of the K_<ATP> channels was unknown. Recently, a high affinity receptor for sulfonylureas (SUR1), a member of the ATP-binding cassette (ABC) superfamily, has been isolated, but it did not elicit K_<ATP> channel currents. We have cloned a member of the inward rectifier K^+ channel family, uK_<ATP>-1 (Kir6.1), which is expressed in various tissues including pancreatic islets, but not in clonal beta-cell lines. Subsequently, we also have cloned BIR (Kir6.2), which belongs to the same subfamily as Kir6.1 and is expressed predominantly in pancreatic islets and clonal beta-cell lines. We have shown that the properties of the K_<ATP> channel reconstituted from SUR1 and Kir6.2 are those described for native pancreatic beta-cells, demonstrating that the pancreatic beta-cell K_<ATP> channel is a complex composed of Kir6.2 and SUR1. We also have isolated a novel sulfonylurea receptor (SUR2) which shares 68% amino acisd identity with SUR1. SUR2 mRNA is abundant in heart and skeletal muscle. Coexpression of SUR2 and Kir6.2 in COS1 cells reconstitutes K_<ATP> channels found in native cardiac and skeletal muscle, indicating that the pharmacological properties of K_<ATP> channels are determined by a family of sulfonylurea receptor subunits. We also have determined the structure and chromosomal localization of human Kir6.2 gene, and have shown that human SUR1 and Kir6.2 genes are clustered at chromosome 11p15.1. We have found several polymorphysms in the Kir6.2 gene and microsatellite DNA polymorphysms close to the Kir6.2 gene, and have shown that genetic variation in the Kir6.2 gene does not play a major role in susceptibility to NIDDM in Japanese and Caucasian.