Sodium Currents in Subthalamic Nucleus Neurons From Nav1.6-Null Mice

Abstract

In some central neurons, including cerebellar Purkinje neurons and subthalamic nucleus (STN) neurons, TTX-sensitive sodium channels show unusual gating behavior whereby some channels open transiently during recovery from inactivation. This “resurgent” sodium current is effectively activated immediately after action potential-like waveforms. Earlier work using Purkinje neurons suggested that the great majority of resurgent current originates from Na_v1.6 sodium channels. Here we used a mouse mutant lacking Na_v1.6 to explore the contribution of these channels to resurgent, transient, and persistent components of TTX-sensitive sodium current in STN neurons. The resurgent current of STN neurons from Na_v1.6^−/− mice was reduced by 63% relative to wild-type littermates, a less dramatic reduction than that observed in Purkinje neurons recorded under identical conditions. The transient and persistent currents of Na_v1.6^−/− STN neurons were reduced by ∼40 and 55%, respectively. The resurgent current present in Na_v1.6^−/− null STN neurons was similar in voltage dependence to that in wild-type STN and Purkinje neurons, differing only in having somewhat slower decay kinetics. These results show that sodium channels other than Na_v1.6 can make resurgent sodium current much like that from Na_v1.6 channels.