Two-pore domain potassium channels: new sites of local anesthetic action and toxicity.

Potassium (K+) channels form the largest family of ion channels with more than 70 such genes identified in the human genome. They are organized in 3 superfamilies according to their predicted membrane topology: (1) subunits with 6 membrane-spanning segments and 1-pore domain, (2) subunits with 2 membrane-spanning segments and 1-pore domain, and (3) subunits with 4 membrane-spanning segments and 2-pore domains arrayed in a tandem position. The last family has most recently been identified and comprises the so-called 2-pore domain potassium (K2P) channels, believed responsible for background or leak K+ currents. Despite their recent discovery, interest in them is growing rapidly with more than 270 references in the literature reported (www.ipmc.cnrs.fr/~duprat/2p/ref2p.htm#2P, accessed October 30, 2004). K2P channels are widely expressed in the central nervous system and are involved in the control of the resting membrane potential and the firing pattern of excitable cells. This article will therefore review recent findings on actions of local anesthetics with respect to 2P channels. It begins with an overview of the role of background K+ channels in neuronal excitability and nerve conduction and is followed by a description of the K2P channel family including experimental evidence for the contribution of K2P channels to the mechanism of action and toxicity of local anesthetics.