Traditional AMPA receptor antagonists partially block Nav1.6-mediated persistent current

Voltage-gated Na channels and AMPA receptors play key roles in neuronal physiology. Moreover, both channels have been implicated in the pathophysiology of both grey and white matter in a variety of conditions. Dissecting out the roles of these channels requires specific pharmacological tools. In this study we examined the potential non-specific effects on Nav1.6 channels of five widely used AMPA receptor blockers. Using whole-cell patch clamp electrophysiology, we identified a TTX-sensitive persistent Na channel current in HEK cells stably expressing the Nav1.6 channel. From a holding potential of −120 mV, slow ramp depolarization to +75 mV generated an inward current that peaked at approximately −15 mV. Superfusion of purportedly specific AMPA antagonists, 1-naphthylacetyl spermine, SYM2206, CP465022, GYKI52466, blocked Nav1.6-mediated persistent currents in a dose-dependent manner. Each of these AMPA receptor blockers significantly inhibited (to ≈70% of control levels) the persistent Na current at concentrations routinely used to selectively block AMPA receptors. The AMPA/kainate blocker, NBQX, did not significantly affect persistent Na channel currents. Furthermore, peak transient current was insensitive to NBQX, but was reversibly inhibited by SYM2206, CP465022 and GYKI52466. These results indicate that many commonly used AMPA receptor antagonists have modest but significant blocking effects on the persistent components of Nav1.6 channel activity; therefore caution should be exercised when ascribing actions to AMPA receptors based on use of these inhibitors.