|Budget Amount *help
¥3,600,000 (Direct Cost : ¥3,600,000)
Fiscal Year 1998 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 1997 : ¥2,600,000 (Direct Cost : ¥2,600,000)
ATP-sensitive K^+(K_<ATP>) channels are key molecules which link the cell's metabolic status to its membrane potential. In pancreatic beta-cells, KK_<ATP> channel is not only a glucose sensor m insulin secretion but also a target for the insulin secretagogue, the sulfonylurea, widely used as oral hypoglycemic agents in the treatment of diabetes mellitus. In cardiac myocytes and neurons, K_<ATP> channels are supposed to be involved in cytoprotection in ischemia, We have shown that beta-cell K_<ATP> channel is a complex of the sulfonylurea receptor SURI and a newly cloned inward rectifier K_<ATP> channel member Kir6.2, and that cardiac myocyte K_<ATP> channel is a complex of the newly cloned sulfonylurea receptor SUR2 and the Kir6.2. Our purpose in this study is to clarify the molecular mechanisms underlying the regulation of K^+ channels.
Sensitivities of the [3-cell (SUR1/Kir6.2) and cardiac (SUR2/Kir6.2) K_<ATP> channels to the sulfonylurea glibenclamide and the K_<ATP> channel opener
diazoxide are different, and are determined by distinct SUR subunits. To determine the domains that confer glibenclamide and diazoxide sensitivities, we prepared a series of chimeras between SUR1 and SUR2, and studied the properties of the chimeric K_<ATP> channels. All chimeric SURs could generate currents when expressed in COS 1 cells with Kir6.2. Next, we have examined the effects of the glibenclamide and diazoxide on the chimeric currents measured as ^<86>Rb^+ efflux, and narrowed the region that confer the sensitivities to these reagents. Furthermore, we have constructed various chimeras between SUR1 and SUR2, and have almost determined the glibenclamide-responsive region by measuring the binding activities of @SH-labeled glibenclamide for the chimeras expressed in COS 1 cells (manuscript in 3@E1preparation).
In addition, we have investigated the effects of G-protein on the reconstituted K_<ATP> channels. We have shown that G-protein alpha subunit directly regulates the K_<ATP> channel activity, and that the regulation is different between [3-cell (SUR1/Kir6.2) and cardiac (SUR2/Kir6.2) K_<ATP> channels, suggesting that the difference is determined by distinct SUR subunits. Less