Ca2+ entry through NaV channels generates submillisecond axonal Ca2+ signaling
- Netherlands Institute for Neuroscience, Netherlands
- Netherlands Institute of Neuroscience, Netherlands
Abstract
Calcium ions (Ca2+) are essential for many cellular signaling mechanisms and enter the cytosol mostly through voltage-gated calcium channels. Here, using high-speed Ca2+ imaging up to 20 kHz in the rat layer 5 pyramidal neuron axon we found that activity-dependent intracellular calcium concentration ([Ca2+]i) in the axonal initial segment was only partially dependent on voltage-gated calcium channels. Instead, [Ca2+]i changes were sensitive to the specific voltage-gated sodium (NaV) channel blocker tetrodotoxin. Consistent with the conjecture that Ca2+ enters through the NaV channel pore, the optically resolved ICa in the axon initial segment overlapped with the activation kinetics of NaV channels and heterologous expression of NaV1.2 in HEK-293 cells revealed a tetrodotoxin-sensitive [Ca2+]i rise. Finally, computational simulations predicted that axonal [Ca2+]i transients reflect a 0.4% Ca2+ conductivity of NaV channels. The findings indicate that Ca2+ permeation through NaV channels provides a submillisecond rapid entry route in NaV-enriched domains of mammalian axons.
Data availability
All data generated or analyzed during this study are included in the manuscript and supporting files. Source data files have been provided for Figures 1 to 7 and Table 1 .
Article and author information
Author details
Naomi A K Hanemaaijer
Oriol Pavón Arocas
Funding
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (865.17.003)
- Maarten H P Kole
Stichting voor Fundamenteel Onderzoek der Materie (16NEPH02)
- Maarten H P Kole
National Multiple Sclerosis Society (RG 4924A1/1)
- Maarten H P Kole
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: All animal experiments were performed in compliance with the European Communities Council Directive 2010/63/EU effective from 1 January 2013. They were evaluated and approved by the national CCD authority (license AVD8010020172426) and by the KNAW animal welfare and ethical guidelines and protocols (DEC NIN 14.49, DEC NIN 12.13, IvD NIN 17.21.01 and 17.21.03).
Human subjects: Written informed consent was obtained from patients and all procedures on human tissue were performed with the approval of the Medical Ethical Committee of the Amsterdam UMC, location VuMC and in accordance with Dutch license procedures and the Declaration of Helsinki. All data were anonymized.
Copyright
© 2020, Hanemaaijer et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Ca2+ entry through NaV channels generates submillisecond axonal Ca2+ signaling
eLife 9:e54566.
https://doi.org/10.7554/eLife.54566
