KCNK9 or TASK-3 (TWIK-related Acid sensitive K+ channel) is a member of the potassium channel family of proteins that contain two-pore domain and four transmembrane domains. These channels are characterized as leak K+ channels that are sensitive to changes in the extracellular pH. The physiological functions of TASK channels are largely unknown; it has been proposed that they may be involved in the regulation of breathing, aldosterone secretion and anesthetic-mediated neuronal activity. They were found to act in neurons' membrane potential and in resting K+ currents. KCNK9 gene has been localized to the chromosomal region 8q24. The protein is expressed at high levels mainly in the brain and at low levels in other tissues. In contrast to normal tissues, it was found that KCNK9 is amplified in some human carcinomas such as breast, lung, colon and metastatic prostate. In 10% of breast cancer patients this gene is amplified, and in 44% the protein is over expressed. Monoclonal antibodies to KNCK9 are an important tool for studying the potassium channel family of proteins in different tissues.