POTASSIUM CHANNELS ACTIVATED BY SODIUM

¹ Department of Physiology, University of Colorado School of Medicine, Denver, CO 80262, USA
² Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA

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.