Slack and Slick KNa channels are required for the depolarizing afterpotential of acutely isolated, medium diameter rat dorsal root ganglion neurons

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 mu m) 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.