ATP-sensitive potassium channels (K_ATP channels) play important roles in various tissues by coupling cell metabolic status to electrical activity. Recently, molecular biological and electrophysiological techniques have revealed the molecular basis of the K_ATP channels to be a complex of the Kir6.0 subunit, a member of the inwardly rectifying K⁺ channel subfamily Kir6.0, and the sulfonylurea receptor (SUR) subunit, a member of ATP-binding cassette (ABC) superfamily; the functional diversity of the various K_ATP channels is being determined by a combination of the Kir6.0 subunit (Kir6.1 or Kir6.2) and the SUR subunit (SUR1 or SUR2) comprising it. Recent studies of the K_ATP channels have suggested mechanisms of K_ATP channel regulation and pathophysiology and also a new model in which ABC proteins regulate the functional expression of ion channels.