NA-ACTIVATED K+ CHANNELS - A NEW FAMILY OF LARGE-CONDUCTANCE ION CHANNELS()

Sodium-activated K+ channels (I(K(Na))) are a class of large-conductan ce ion channels expressed in several populations of vertebrate neurons , mammalian cardiac myocytes and Xenopus oocytes. These channels are a ctivated by the binding of Na+ to sites located an the cytoplasmic fac e of the channel. The physiological functions of I(K(Na)) channels hav e been difficult to ascertain, in part because their activation typica lly requires Na+ concentrations considerably higher than those that ar e normally present in the cytosol. However, there is now evidence sugg esting that I(K(Na)) can play a role in the regulation of neuronal exc itability, the modulation of the action-potential waveform, and the re sponses of excitable cells to hypoxia and ischemia.