Persistent sodium current decreases transient gain in turtle motoneurons

Abstract

Voltage dependent ion channels can influence signal integration in neurons dramatically. In addition to the classical fast-inactivating Na(+) current that mediates action potentials, many neurons also express persistent sodium current (I(NaP)). Activating at membrane potentials below the threshold for action potentials, this current may amplify excitatory postsynaptic potentials and shape the firing patterns. To determine the qualitative contribution of I(NaP) to the intrinsic firing properties of motoneurons, we eliminated this current by dynamic clamp. As expected, we found that elimination of I(NaP) shifted the rheobase to more positive currents. More interestingly, elimination of I(NaP) increased the steepness of initial frequency-to-current (fI) relation. This suggests that I(NaP) decreases the transient gain and broadens the integration window for short synaptic inputs in spinal motoneurons.