Acta Pharmacologica Sinica 2008 August; 29 (8): 899-905; doi 10.1111/j.1745-7254.2008.00842.x

Aim: Na⁺-activated K⁺ (K_Na) channels set and stabilize resting membrane potential in rat small dorsal root ganglion (DRG) neurons. However, whether K_Na channels play the same role in other size DRG neurons is still elusive. The aim of this study is to identify the existence and potential physiological functions of K_Na channels in medium diameter (25_35 μm) DRG neurons.

Methods: Inside-out and whole-cell patch-clamp were used to study the electrophysiological characterizations of native K_Na channels. RT_PCR was used to identify the existence of Slack and Slick genes.

Results: We report that K_Na channels are required for depolarizing afterpotential (DAP) in medium sized rat DRG neurons. In inside-out patches, K_Na channels represented 201 pS unitary chord conductance and were activated by cytoplasmic Na⁺ [the half maximal effective concentration (EC₅₀): 35 mmol/L] in 160 mmol/L symmetrical K⁺_o/K⁺_i solution. Additionally, these K_Na channels also represented cytoplasmic Cl^_-dependent activation. RT_PCR confirmed the existence of Slack and Slick genes in DRG neurons. Tetrodotoxin (TTX, 100 nmol/L) completely blocked the DRG inward Na⁺ currents, and the following outward currents which were thought to be K_Na currents. The DAP was increased when extracellular Na⁺ was replaced by Li⁺.

Conclusion: We conclude that Slack and Slick K_Na channels are required for DAP of medium diameter rat DRG neurons that regulate DRG action potential repolarization.

Keywords: Slack; Slick; Na⁺-activated K⁺ channels; depolarizing afterpotential; dorsal root ganglion