Potassium Channels Activated by Sodium

Na+-activated K+ currents have been reported in snail neurones, crayfish giant motoneurones, cardiac myocytes, and in ganglion cells and brain stem cells from chick embryos. Such currents are seen in voltage-clamp experiments, following depolarization-induced Na+ influx. A variety of experiments have shown that the currents through the conductance pathways are indeed carried by K+ ions and that they are quantitatively dependent upon Na+ influx into the cells. Theoretical calculations indicate that such currents must make a substantial contribution to action potential repolarization. The conductances are activated by Li+ in invertebrate neurones, but not in the embryonic vertebrate neurones. Single-channel recordings from vertebrate brain stem cells reveal channels with conductances of about 50 pS, activated by Na+ concentrations in the 10-100 mM range.