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.