Skip to main content
  • Poster presentation
  • Open access
  • Published:

Axon initial segment potassium channel density in cortical neurons

There is a growing interest in estimating actual density ranges of Na+ channels in the very thin axon, especially in the action potential (AP) initiation zone, i.e., the axon initial segment (AIS, 20-50 microns away from the cell body). Both immunostaining studies and patch-clamp recordings indicated a relatively high density of Na+ channels in AIS of either pyramidal regular-spiking (RS) cells [1] or fast-spiking (FS) GABAergic interneurons [2, 3]. Here, we investigated potassium channel densities in AISs of both RS and FS cells in same recording conditions.

Our axonal recordings directly revealed that there is a very lower potassium density gK = 185.8±19 pS/µm2 N = 16) for the RS AIS while a higher gK (495.7±108 pS/µm2, N = 11) for FS AIS, see Figure 1A. For both the RS pyramidal cells and FS PV cells, partially blocking K+ channels by applying 4-AP broadened the spike duration and decreased the dV/dt ratio significantly (P < 0.05) (For RS cells: N = 5; For RS cells: N = 4). Interestingly, we observed that the AP dV/dt ratio is an exponentially decaying function of the spike duration for both RS- and FS-spikings (see Figure 1B), such that y = 0.12+0.16EXP((0.5-x)/0.2), where y represents the dV/dt ratio and × represents the AP duration. These observations suggest strongly that potassium channel density is one of the major intrinsic factors dominating the spike shape properties, especially half-height spike duration and dV/dt ratio.

Figure 1
figure 1

A. The bar graph shows peak K+ conductance density recorded in axon initial segment of cells (16 recording axons for RS pyramidal cell, 11 for FS interneuron) by outside-out axon patch recording technique. B. Summary of the results from partially blocking K+ channels. The AP dV/dt ratio is an exponentially decaying function of the spike duration.

In sum, the significant difference in potassium channel density in axonal initial segment where action potentials are initiated may play a critical role in controlling action potential properties of both RS- and FS-spiking cells in nervous system by the same general biophysical rule. These results may be important for constructing computational models of different types of cortical neurons.


  1. Hu W, Tian C, Li T, Yang M, Hou H, Shu Y: Distinct contributions of Na(v)1.6 and Na(v)1.2 in action potential initiation and backpropagation. Nat Neurosci. 2009, 12 (8): 996-1002.

    Article  PubMed  CAS  Google Scholar 

  2. Hu H, Jonas P: A supercritical density of Na(+) channels ensures fast signaling in GABAergic interneuron axons. Nat Neurosci. 2014, 17 (5): 686-693.

    Article  PubMed  CAS  PubMed Central  Google Scholar 

  3. Li T, Tian C, Scalmani P, Frassoni C, Mantegazza M, Wang Y, Yang M, Wu S, Shu Y: Action potential initiation in neocortical inhibitory interneurons. PLoS Biol. 2014, 12 (9): e1001944-

    Article  PubMed  PubMed Central  Google Scholar 

Download references


This project is funded by NNSF of China (31271170) and Eastern Scholar SHH1140004) at Shanghai Institutions of Higher Learning.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Yuguo Yu.

Rights and permissions

Open Access  This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.

The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

To view a copy of this licence, visit

The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Zhang, W., Fan, B., Zheng, P. et al. Axon initial segment potassium channel density in cortical neurons. BMC Neurosci 16 (Suppl 1), P295 (2015).

Download citation

  • Published:

  • DOI: