Na+ imaging reveals little difference in action potential-evoked Na+ influx between axon and soma

Nat Neurosci. 2010 Jul;13(7):852-60. doi: 10.1038/nn.2574. Epub 2010 Jun 13.


In cortical pyramidal neurons, the axon initial segment (AIS) is pivotal in synaptic integration. It has been asserted that this is because there is a high density of Na(+) channels in the AIS. However, we found that action potential-associated Na(+) flux, as measured by high-speed fluorescence Na(+) imaging, was about threefold larger in the rat AIS than in the soma. Spike-evoked Na(+) flux in the AIS and the first node of Ranvier was similar and was eightfold lower in basal dendrites. At near-threshold voltages, persistent Na(+) conductance was almost entirely axonal. On a time scale of seconds, passive diffusion, and not pumping, was responsible for maintaining transmembrane Na(+) gradients in thin axons during high-frequency action potential firing. In computer simulations, these data were consistent with the known features of action potential generation in these neurons.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Action Potentials / physiology*
  • Animals
  • Axons / metabolism*
  • Cell Membrane
  • In Vitro Techniques
  • Ion Transport / physiology
  • Pyramidal Cells / metabolism*
  • Ranvier's Nodes / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Signal Transduction / physiology*
  • Sodium / metabolism
  • Sodium Channels / metabolism*
  • Somatosensory Cortex / cytology
  • Somatosensory Cortex / metabolism
  • Synaptic Transmission


  • Sodium Channels
  • Sodium