Na+ imaging reveals little difference in action potential-evoked Na+ influx between axon and soma.
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.
Fleidervish
Ilya A
IA
Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel. ilya@bgu.ac.il
Lasser-Ross
Nechama
N
Gutnick
Michael J
MJ
Ross
William N
WN
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002462:Cell Membrane; D066298:In Vitro Techniques; D017136:Ion Transport / Q000502:physiology; D017966:Pyramidal Cells / Q000378:metabolism*; D011901:Ranvier's Nodes / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D013003:Somatosensory Cortex / Q000166:cytology / Q000378:metabolism; D009435:Synaptic Transmission
D015222:Sodium Channels; D012964:Sodium