Two-pore domain potassium channels, such as KCNK18, give rise to background, or leak, potassium conductance, and they regulate diverse cellular functions by adjusting both the resting membrane potential and excitability. KCNK18 is unique among this family of potassium channels in that its activity is regulated by intracellular calcium (summary by Czirjak and Enyedi, 2006 [PubMed 16569637]).