Molecular and functional properties of two-pore-domain potassium channels.

The two-pore-domain K(+) channels, or K(2P) channels, constitute a novel class of K(+) channel subunits. They have four transmembrane segments and are active as dimers. The tissue distribution of these channels is widespread, and they are found in both excitable and nonexcitable cells. K(2P) channels produce currents with unusual characteristics. They are quasi-instantaneous and noninactivating, and they are active at all membrane potentials and insensitive to the classic K(+) channel blockers. These properties designate them as background K(+) channels. They are expected to play a major role in setting the resting membrane potential in many cell types. Another salient feature of K(2P) channels is the diversity of their regulatory mechanisms. The weak inward rectifiers TWIK-1 and TWIK-2 are stimulated by activators of protein kinase C and decreased by internal acidification, the baseline TWIK-related acid-sensitive K(+) (TASK)-1 and TASK-2 channels are sensitive to external pH changes in a narrow range near physiological pH, and the TWIK-related (TREK)-1 and TWIK-related arachidonic acid-stimulated K(+) (TRAAK) channels are the first cloned polyunsaturated fatty acids-activated and mechanogated K(+) channels. The recent demonstration that TASK-1 and TREK-1 channels are activated by inhalational general anesthetics, and that TRAAK is activated by the neuroprotective agent riluzole, indicates that this novel class of K(+) channels is an interesting target for new therapeutic developments.