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

Abstract

Aim: Na+-activated K+ (KNa) channels set and stabilize resting membrane potential in rat small dorsal root ganglion (DRG) neurons. However, whether KNa 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 KNa 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 KNa channels. RT-PCR was used to identify the existence of Slack and Slick genes. Results: We report that KNa channels are required for depolarizing afterpotential (DAP) in medium sized rat DRG neurons. In inside-out patches, KNa 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 KNa 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 KNa currents. The DAP was increased when extracellular Na+ was replaced by Li+. Conclusion: We conclude that Slack and Slick KNa channels are required for DAP of medium diameter rat DRG neurons that regulate DRG action potential repolarization. © 2008 CPS and SIMM.