For K⁺ channels, Na⁺ is the new Ca²⁺

Although K⁺ channels activated by Ca²⁺ have long been known to shape neuronal excitability, evidence is accumulating that K ⁺ channels sensitive to intracellular Na⁺, termed K _Na channels, have an equally significant role. K_Na channels contribute to adaptation of firing rate and to slow afterhyperpolarizations that follow repetitive firing. In certain neurons, they also appear to be activated by Na⁺ influx accompanying a single spike. Two genes encoding these channels, Slick and Slack, are expressed throughout the brain. The spatial localization of K_Na channels along axons, dendrites and somata appears to be highly cell-type specific. Their molecular properties also suggest that these channels contribute to the response of neurons to hypoxia.