Sodium Channels in Axons and Glial Cells of the Optic Nerve of Necturus maculosa

I N T R O D U C T I O N It is generally accepted that glial cells provide mechanical and, perhaps, metabol ic support for the neuronal cells that they surround but do not par t ic ipate directly in the events of excitabil i ty (Nakai, 1963; Kuff ler and Nicholls, 1966). However, in 1976 Villegas et al. (1976) reported electrophysiological evidence for the existence of sodium channels in Schwann cells of squid giant axons. The m e m b r a n e of these Schwann cells was depolarized by drugs that were known to act ivate the vol tage-dependent sodium channels in resting excitable membranes , and such depolarizat ions were reversed by te t rodotoxin (TTX) , a d rug that specifically blocks these sodium channels (Kao, 1966). This provocative result, if t rue in other excitable tissues, demands J. GEN. PHYSIOL. 9 Rockefeller Universi ty Press 9 0022-1295 /79 /11 /0629 /14 SI.00 629 Volume 74 November 1979 629--642 on Jne 4, 2017 D ow nladed fom Published November 1, 1979