The two-pore-domain potassium channel (not to be confused with the small family of two-pore channels) a family of 15 members form what is known as "leak channels" which possess Goldman-Hodgkin-Katz (open) rectification. These channels are regulated by several mechanisms including oxygen tension, pH, mechanical stretch, and G-proteins .[citation needed] Their name is derived from the fact that the α subunits consist of four transmembrane segments, each containing two pore loops. As such, they structurally correspond to two inward-rectifier α subunits and thus form dimers in the membrane.Below is a list of the 15 known two-pore-domain human potassium channels: