Roles of ATP-sensitive K+ channels as metabolic sensors: studies of Kir6.x null mice.

ATP-sensitive K+ channels (KATP channels) are present in various tissues, including pancreatic beta-cells, heart, skeletal muscles, vascular smooth muscles, and brain. KATP channels are hetero-octameric proteins composed of inwardly rectifying K+ channel (Kir6.x) and sulfonylurea receptor (SUR) subunits. Different combinations of Kir6.x and SUR subunits comprise KATP channels with distinct electrophysiological and pharmacological properties. Recent studies of genetically engineered mice have provided insight into the physiological and pathophysiological roles of Kir6.x-containing KATP channels. Analysis of Kir6.2 null mice has shown that Kir6.2/SUR1 channels in pancreatic beta-cells and the hypothalamus are essential in glucose-induced insulin secretion and hypoglycemia-induced glucagon secretion, respectively, and that Kir6.2/SUR2 channels are involved in glucose uptake in skeletal muscles. Kir6.2-containing KATP channels in brain also are involved in protection from hypoxia-induced generalized seizure. In cardiovascular tissues, Kir6.1-containing KATP channels are involved in regulation of vascular tonus. In addition, the Kir6.1 null mouse is a model of Prinzmetal angina in humans. Our studies of Kir6.2 null and Kir6.1 null mice reveal that KATP channels are critical metabolic sensors in acute metabolic changes, including hyperglycemia, hypoglycemia, ischemia, and hypoxia.