Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

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

Abstract

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.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Time course of action potential–induced [Na+]i changes is different in different compartments.
Figure 2: Active transport cannot account for the rapid Na+ clearance in the axon.
Figure 3: Axonal Na+ transients reflect localized Na+ influx into the AIS followed by diffusion to the soma and first myelinated internode.
Figure 4: The shape of spike-evoked Na+ transients constrains the ratio of Na+ channel densities in different compartments.
Figure 5: Relative spike-evoked Na+ flux in different neuronal compartments.
Figure 6: Action potential–evoked Na+ charge transfer in nodes of Ranvier is comparable to the transfer in the AIS.
Figure 7: At subthreshold voltages, persistent Na+ current is generated predominately in the AIS.
Figure 8: Compartmental model of an action potential that matches the fast maximal rates of rise of recorded spikes and initiates in the axon without requiring a high AIS Na+ channel density.

Similar content being viewed by others

References

  1. Kole, M.H. & Stuart, G.J. Is action potential threshold lowest in the axon? Nat. Neurosci. 11, 1253–1255 (2008).

    Article  CAS  Google Scholar 

  2. Colbert, C.M. & Pan, E. Ion channel properties underlying axonal action potential initiation in pyramidal neurons. Nat. Neurosci. 5, 533–538 (2002).

    Article  CAS  Google Scholar 

  3. Kole, M.H. et al. Action potential generation requires a high sodium channel density in the axon initial segment. Nat. Neurosci. 11, 178–186 (2008).

    Article  CAS  Google Scholar 

  4. Hu, W. et al. Distinct contributions of Na(v)1.6 and Na(v)1.2 in action potential initiation and backpropagation. Nat. Neurosci. 12, 996–1002 (2009).

    Article  CAS  Google Scholar 

  5. Stuart, G. & Sakmann, B. Amplification of EPSPs by axosomatic sodium channels in neocortical pyramidal neurons. Neuron 15, 1065–1076 (1995).

    Article  CAS  Google Scholar 

  6. Astman, N., Gutnick, M.J. & Fleidervish, I.A. Persistent sodium current in layer 5 neocortical neurons is primarily generated in the proximal axon. J. Neurosci. 26, 3465–3473 (2006).

    Article  CAS  Google Scholar 

  7. Mainen, Z.F., Joerges, J., Huguenard, J.R. & Sejnowski, T.J. A model of spike initiation in neocortical pyramidal neurons. Neuron 15, 1427–1439 (1995).

    Article  CAS  Google Scholar 

  8. Colbert, C.M. & Johnston, D. Axonal action-potential initiation and Na+ channel densities in the soma and axon initial segment of subicular pyramidal neurons. J. Neurosci. 16, 6676–6686 (1996).

    Article  CAS  Google Scholar 

  9. Minta, A. & Tsien, R.Y. Fluorescent indicators for cytosolic sodium. J. Biol. Chem. 264, 19449–19457 (1989).

    CAS  PubMed  Google Scholar 

  10. Callaway, J.C. & Ross, W.N. Spatial distribution of synaptically activated sodium concentration changes in cerebellar Purkinje neurons. J. Neurophysiol. 77, 145–152 (1997).

    Article  CAS  Google Scholar 

  11. Palmer, L.M. & Stuart, G.J. Site of action potential initiation in layer 5 pyramidal neurons. J. Neurosci. 26, 1854–1863 (2006).

    Article  CAS  Google Scholar 

  12. Lelievre, L., Zachowski, A., Charlemagne, D., Laget, P. & Paraf, A. Inhibition of (Na+ + K+)–ATPase by ouabain: involvement of calcium and membrane proteins. Biochim. Biophys. Acta 557, 399–408 (1979).

    Article  CAS  Google Scholar 

  13. Kushmerick, M.J. & Podolsky, R.J. Ionic mobility in muscle cells. Science 166, 1297–1298 (1969).

    Article  CAS  Google Scholar 

  14. Clark, B.A., Monsivais, P., Branco, T., London, M. & Hausser, M. The site of action potential initiation in cerebellar Purkinje neurons. Nat. Neurosci. 8, 137–139 (2005).

    Article  CAS  Google Scholar 

  15. Rose, C.R., Kovalchuk, Y., Eilers, J. & Konnerth, A. Two-photon Na+ imaging in spines and fine dendrites of central neurons. Pflugers Arch. 439, 201–207 (1999).

    CAS  PubMed  Google Scholar 

  16. Peters, A. The node of Ranvier in the central nervous system. Q. J. Exp. Physiol. Cogn. Med. Sci. 51, 229–236 (1966).

    CAS  PubMed  Google Scholar 

  17. Fleidervish, I.A. & Gutnick, M.J. Kinetics of slow inactivation of persistent sodium current in layer V neurons of mouse neocortical slices. J. Neurophysiol. 76, 2125–2130 (1996).

    Article  CAS  Google Scholar 

  18. Alzheimer, C., Schwindt, P.C. & Crill, W.E. Modal gating of Na+ channels as a mechanism of persistent Na+ current in pyramidal neurons from rat and cat sensorimotor cortex. J. Neurosci. 13, 660–673 (1993).

    Article  CAS  Google Scholar 

  19. Kole, M.H., Letzkus, J.J. & Stuart, G.J. Axon initial segment Kv1 channels control axonal action potential waveform and synaptic efficacy. Neuron 55, 633–647 (2007).

    Article  CAS  Google Scholar 

  20. Engel, D. & Jonas, P. Presynaptic action potential amplification by voltage-gated Na+ channels in hippocampal mossy fiber boutons. Neuron 45, 405–417 (2005).

    Article  CAS  Google Scholar 

  21. Royeck, M. et al. Role of axonal NaV1.6 sodium channels in action potential initiation of CA1 pyramidal neurons. J. Neurophysiol. 100, 2361–2380 (2008).

    Article  CAS  Google Scholar 

  22. Carter, B.C. & Bean, B.P. Sodium entry during action potentials of mammalian neurons: incomplete inactivation and reduced metabolic efficiency in fast-spiking neurons. Neuron 64, 898–909 (2009).

    Article  CAS  Google Scholar 

  23. Bender, K.J. & Trussell, L.O. Axon initial segment Ca2+ channels influence action potential generation and timing. Neuron 61, 259–271 (2009).

    Article  CAS  Google Scholar 

  24. Lasser-Ross, N. & Ross, W.N. Imaging voltage and synaptically activated sodium transients in cerebellar Purkinje cells. Proc. Biol. Sci. 247, 35–39 (1992).

    Article  CAS  Google Scholar 

  25. Alle, H., Roth, A. & Geiger, J.R. Energy-efficient action potentials in hippocampal mossy fibers. Science 325, 1405–1408 (2009).

    Article  CAS  Google Scholar 

  26. Nevian, T., Larkum, M.E., Polsky, A. & Schiller, J. Properties of basal dendrites of layer 5 pyramidal neurons: a direct patch-clamp recording study. Nat. Neurosci. 10, 206–214 (2007).

    Article  CAS  Google Scholar 

  27. Acker, C.D. & Antic, S.D. Quantitative assessment of the distributions of membrane conductances involved in action potential backpropagation along basal dendrites. J. Neurophysiol. 101, 1524–1541 (2009).

    Article  Google Scholar 

  28. Bean, B.P. The action potential in mammalian central neurons. Nat. Rev. Neurosci. 8, 451–465 (2007).

    Article  CAS  Google Scholar 

  29. Sugihara, I., Lang, E.J. & Llinas, R. Uniform olivocerebellar conduction time underlies Purkinje cell complex spike synchronicity in the rat cerebellum. J. Physiol. (Lond.) 470, 243–271 (1993).

    Article  CAS  Google Scholar 

  30. Markram, H., Lubke, J., Frotscher, M. & Sakmann, B. Regulation of synaptic efficacy by coincidence of postsynaptic APs and EPSPs. Science 275, 213–215 (1997).

    Article  CAS  Google Scholar 

  31. Shrager, P. The distribution of sodium and potassium channels in single demyelinated axons of the frog. J. Physiol. (Lond.) 392, 587–602 (1987).

    Article  CAS  Google Scholar 

  32. Zhang, C.L., Wilson, J.A., Williams, J. & Chiu, S.Y. Action potentials induce uniform calcium influx in mammalian myelinated optic nerves. J. Neurophysiol. 96, 695–709 (2006).

    Article  CAS  Google Scholar 

  33. Attwell, D. & Iadecola, C. The neural basis of functional brain imaging signals. Trends Neurosci. 25, 621–625 (2002).

    Article  CAS  Google Scholar 

  34. Mata, M., Fink, D.J., Ernst, S.A. & Siegel, G.J. Immunocytochemical demonstration of Na+,K+-ATPase in internodal axolemma of myelinated fibers of rat sciatic and optic nerves. J. Neurochem. 57, 184–192 (1991).

    Article  CAS  Google Scholar 

  35. Larkum, M.E., Watanabe, S., Nakamura, T., Lasser-Ross, N. & Ross, W.N. Synaptically activated Ca2+ waves in layer 2/3 and layer 5 rat neocortical pyramidal neurons. J. Physiol. (Lond.) 549, 471–488 (2003).

    Article  CAS  Google Scholar 

  36. Stuart, G.J., Dodt, H.U. & Sakmann, B. Patch-clamp recordings from the soma and dendrites of neurons in brain slices using infrared video microscopy. Pflugers Arch. 423, 511–518 (1993).

    Article  CAS  Google Scholar 

  37. Helmchen, F., Imoto, K. & Sakmann, B. Ca2+ buffering and action potential–evoked Ca2+ signaling in dendrites of pyramidal neurons. Biophys. J. 70, 1069–1081 (1996).

    Article  CAS  Google Scholar 

  38. Neher, E. & Augustine, G.J. Calcium gradients and buffers in bovine chromaffin cells. J. Physiol. (Lond.) 450, 273–301 (1992).

    Article  CAS  Google Scholar 

  39. Hodgkin, A.L. & Keynes, R.D. Experiments on the injection of substances into squid giant axons by means of a microsyringe. J. Physiol. (Lond.) 131, 592–616 (1956).

    Article  CAS  Google Scholar 

  40. Hines, M.L. & Carnevale, N.T. The NEURON simulation environment. Neural Comput. 9, 1179–1209 (1997).

    Article  CAS  Google Scholar 

  41. Stuart, G., Schiller, J. & Sakmann, B. Action potential initiation and propagation in rat neocortical pyramidal neurons. J. Physiol. (Lond.) 505, 617–632 (1997).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

We thank S. Manita for excellent help with the preparation of slices. This work was supported by a US-Israel Binational Science Foundation grant (2003082), a grant from the Israel Science Foundation (1376-06), a Grass Faculty grant from the Marine Biological Laboratory, a US National Institutes of Health grant (NS16295), a Multiple Sclerosis Society grant (PP1367) and a fellowship from the Gruss Lipper Foundation.

Author information

Authors and Affiliations

Authors

Contributions

I.A.F., N.L.-R., M.J.G. and W.N.R. designed the study, performed the cortical experiments and wrote the paper. N.L.-R. and W.N.R. performed the cerebellar experiments. I.A.F. constructed the computational models.

Corresponding author

Correspondence to Ilya A Fleidervish.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–5 (PDF 1489 kb)

Supplementary Movie 1

Single action potential elicited a prominent change in [Na+]i in the AIS. The changes in [Na+]i in the soma and in the nearby basal dendrites were too small to be detected. (MPG 942 kb)

Supplementary Movie 2

In a model with the equal Na+ channel density in soma and AIS (250 pS μm−2), somatic current injection (1 nA, 3 ms) produces a relatively slowly rising action potential that initiates simultaneously in soma and in nearby processes. Waveform represents membrane potential across the axo-dendritic axes at different time points starting 1 ms before the beginning of the current step and ending 0.5 ms after its end. (WMV 568 kb)

Supplementary Movie 3

In a model that assumes the AIS Na+ channel density threefold higher than in the soma, the time constant of Na+ channels activation accelerated (τm × 0.2; see Fig. 8a) and persistent Na+ conductance which comprises 5% of the total AIS Na+ conductance, the spike initiates in the AIS, propagates rapidly into the axon and more slowly into the soma and the apical dendrite. Same time window as in Supplementary Movie 2. (WMV 603 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Fleidervish, I., Lasser-Ross, N., Gutnick, M. et al. Na+ imaging reveals little difference in action potential–evoked Na+ influx between axon and soma. Nat Neurosci 13, 852–860 (2010). https://doi.org/10.1038/nn.2574

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nn.2574

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing