Published 23 July 2001. doi:10.1083/jcb1542iti4
© The Rockefeller University Press,
0021-9525/2001/7/253-a $5.00
The Journal of Cell Biology, Volume 154, Number 2, July 23, 2001 253-a-253
Bringing channels into the node
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Sodium channels (white) cluster at nodes of Ranvier.
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Nodes of Ranvier, the unmyelinated segments of myelinated axons, bear high concentrations of sodium channels to propagate action potentials from node to node. Ratcliffe et al. (page 427) suggest that the sodium channels are recruited to the nodes by interacting through their ß subunits with neurofascin, one of the first molecules found in developing nodes of Ranvier.
The interaction of the ß subunits with neurofascin, long known to be a cell adhesion molecule in neurons, did not come entirely as a surprise, since ß subunits show sequence homology to cell adhesion molecules. This paper provides new evidence that the ß subunits of sodium channels perform a dual role: anchoring the sodium channel through lateral interactions in the plasma membrane, as well as their known function of speeding up the opening and closing of sodium channels.
The authors transfected cells in tissue culture to show that neurofascin interacts with the ß1 and ß3 subunits of sodium channels, but not the ß2 subunit, and that the interaction between neurofascin and ß1 occurs within the same cell, rather than between adjacent cells. The ß1 subunit and neurofascin are both concentrated at nodes of Ranvier in the developing rat brain, as well as in the adult brain. The authors propose that this interaction helps concentrate sodium channels at the nodes of Ranvier. Interestingly, both the ß1 subunit and neurofascin bind to ankyrin-G, a protein in the cytoplasm, suggesting that proteins inside the cell guide the assembly of proteins at the node. 
Karin Jegalian
jegalian{at}nasw.org
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