K⁺ channels sensitive to intracellular Na⁺, termed K_Na channels, shape neuronal excitability. K_Na channels contribute to the adaptation of firing rates and to slow after-hyperpolarizations that follow repetitive firing. In certain neurons, they also appear to be activated by Na⁺ influx accompanying single action potentials. Their molecular properties also suggest that these channels contribute to the response of neurons to hypoxia.