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© The Rockefeller University Press, 0021-9525/1998//675 $5.00
The Journal of Cell Biology, Volume 140, Number 3, , 1998 675-684

Article

β-Spectrin Is Colocalized with Both Voltage-gated Sodium Channels and AnkyrinG at the Adult Rat Neuromuscular Junction



S.J. Wood and C.R. Slater

School of Neurosciences, The Medical School, University of Newcastle upon Tyne NE2 4HH, United Kingdom

Voltage-gated sodium channels (VGSCs) are concentrated in the depths of the postsynaptic folds at mammalian neuromuscular junctions (NMJs) where they facilitate action potential generation during neuromuscular transmission. At the nodes of Ranvier and the axon hillocks of central neurons, VGSCs are associated with the cytoskeletal proteins, β-spectrin and ankyrin, which may help to maintain the high local density of VGSCs. Here we show in skeletal muscle, using immunofluorescence, that β-spectrin is precisely colocalized with both VGSCs and ankyrinG, the nodal isoform of ankyrin. In en face views of rat NMJs, acetylcholine receptors (AChRs), and utrophin immunolabeling are organized in distinctive linear arrays corresponding to the crests of the postsynaptic folds. In contrast, β-spectrin, VGSCs, and ankyrinG have a punctate distribution that extends laterally beyond the AChRs, consistent with a localization in the depths of the folds. Double antibody labeling shows that β-spectrin is precisely colocalized with both VGSCs and ankyrinG at the NMJ. Furthermore, quantification of immunofluorescence in labeled transverse sections reveals that β-spectrin is also concentrated in perijunctional regions, in parallel with an increase in labeling of VGSCs and ankyrinG, but not of dystrophin. These observations suggest that interactions with β-spectrin and ankyrinG help to maintain the concentration of VGSCs at the NMJ and that a common mechanism exists throughout the nervous system for clustering VGSCs at a high density.

Abbreviations used in this paper: AChRs, acetylcholine receptors; BgTx, bungarotoxin; ETA, epitrochleoanconeous; J, junctional; NMJ, neuromuscular junction; PJ, perijunctional; RBC, red blood cell; VGSC, voltage-gated sodium channel; XJ, extrajunctional.

This project was supported by grants from the Muscular Dystrophy Group of Great Britain and the Myasthenia Gravis Association.

Address all correspondence to S.J. Wood's present address, Department of Physiology, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK. Tel.: 44-117-928-7821. Fax: 44-117-928-8923. E-mail: s.j.wood{at}bristol.ac.uk


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