Subunit of ATP-sensitive potassium channels (KATP). Can form cardiac and smooth muscle-type KATP channels with KCNJ11. KCNJ11 forms the channel pore while ABCC9 is required for activation and regulation. Interacts with KCNJ11. Expressed at high levels in heart, skeletal muscle and ovary. Moderate levels are found in brain, tongue and pancreatic islets. Low levels are found in lung, testis and adrenal gland. Expressed at very low levels in stomach, colon, thyroid and pituitary. Belongs to the ABC transporter superfamily. ABCC family. Conjugate transporter (TC 3.A.1.208) subfamily.