Decreases in metabolic ATP open K channels and reduce firing in an auditory brainstem neuron: A dynamic mechanism of firing control during intense activity.

Cartwheel (CW) neurons are glycinergic interneurons in the dorsal cochlear nucleus (DCN) that exhibit spontaneous firing, resulting in potent tonic inhibition of fusiform neurons. CW neurons expressing open ATP-sensitive potassium (K) channels do not fire spontaneously, and activation of K channels halts spontaneous firing in these neurons. However, the conditions that regulate K channel opening in CW neurons remain unknown. Here, we tested the hypothesis that fluctuations in metabolic ATP levels modulate K channels in CW neurons. Using whole-cell patch-clamp recordings in CW neurons from young rat brain slices (p17-22) with an ATP-free internal solution, we observed that the mitochondrial uncoupler CCCP hyperpolarized the membrane potential, reduced spontaneous firing, and generated an outward current, which was inhibited by the K channel antagonist tolbutamide. Additionally, a glucose-free external solution quickly activated K channels and ceased spontaneous firing. We hypothesized that intense membrane ion ATPase activity during strong depolarization would deplete intracellular ATP, leading to K channel opening. Consistent with this, depolarizing CW neurons with a 250 pA DC did not increase spontaneous firing because the depolarization activated K channels; however, the same depolarization after tolbutamide administration increased firing, suggesting that ATP depletion triggered K channel opening to limit action potential firing. These results indicate that K channels in the DCN provide dynamic control over action potential firing, preventing excessive excitation during high-firing activity.