Differential modulation of Nav1.7 and Nav1.8 peripheral nerve sodium channels by the local anesthetic lidocaine.

1 Voltage-gated Na+ channels are transmembrane proteins that are essential for the propagation of action potentials in excitable cells. Nav1.7 and Nav1.8 dorsal root ganglion Na+ channels exhibit different kinetics and sensitivities to tetrodotoxin (TTX). We investigated the properties of both channels in the presence of lidocaine, a local anesthetic (LA) and class I anti-arrhythmic drug. 2 Nav1.7 and Nav1.8 Na+ channels were coexpressed with the beta1-subunit in Xenopus oocytes. Na+ currents were recorded using the two-microelectrode voltage-clamp technique. 3 Dose-response curves for both channels had different EC50 (dose producing 50% maximum current inhibition) (450 microm for Nav1.7 and 104 microm for Nav1.8). Lidocaine enhanced current decrease in a frequency-dependent manner. Steady-state inactivation of both channels was also affected by lidocaine, Nav1.7 being the most sensitive. Only the steady-state activation of Nav1.8 was affected while the entry of both channels into slow inactivation was affected by lidocaine, Nav1.8 being affected to a larger degree. 4 Although the channels share homology at DIV S6, the LA binding site, they differ in their sensitivity to lidocaine. Recent studies suggest that other residues on DI and DII known to influence lidocaine binding may explain the differences in affinities between Nav1.7 and Nav1.8 Na+ channels. 5 Understanding the properties of these channels and their pharmacology is of critical importance to developing drugs and finding effective therapies to treat chronic pain.