Journal
JOURNAL OF NEUROSCIENCE
Volume 30, Issue 30, Pages 10233-10242Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.6335-09.2010
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Funding
- Deutsche Forschungsgemeinschaft [SFB 780/B3, Bi 642/2]
- Gatsby Charitable Foundation
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Action potentials (APs) are initiated in the proximal axon of most neurons. In myelinated axons, a 50-times higher sodium channel density in the initial segment compared to the soma may account for this phenomenon. However, little is known about sodium channel density and gating in proximal unmyelinated axons. To study the mechanisms underlying AP initiation in unmyelinated hippocampal mossy fibers of adult mice, we recorded sodium currents in axonal and somatic membrane patches. We demonstrate that sodium channel density in the proximal axon is similar to 5 times higher than in the soma. Furthermore, sodium channel activation and inactivation are similar to 2 times faster. Modeling revealed that the fast activation localized the initiation site to the proximal axon even upon strong synaptic stimulation, while fast inactivation contributed to energy-efficient membrane charging during APs. Thus, sodium channel gating and density in unmyelinated mossy fiber axons appear to be specialized for robust AP initiation and propagation with minimal current flow.
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