 The association of four Kir6.x and four SUR subunits form an ion conducting channel commonly referred to as the KATP channel.Three forms of the sulfonylurea receptor are known, SUR1 encoded by the "ABCC8" gene, and SUR2A and SUR2B, which are splice variants arising from a single "ABCC9" gene.The primary function of the sulfonylurea receptor is to sense intracellular levels of the nucleotides ATP and ADP and in response facilitate the open or closing its associated Kir6.x potassium channel.