Journal of Neuroscience, Vol 3, 995-1003, Copyright © 1983 by Society for Neuroscience
Development of sodium channels during differentiation of chick skeletal muscle in culture. I. Binding studies
J Baumgold, JB Parent and I Spector
[125I]Scorpion toxin and [3H]saxitoxin, two neurotoxins that bind
specifically to different sites on sodium channels, were used to monitor
the development of sodium channels during synchronous differentiation of
chick skeletal muscle in culture. [3H]Saxitoxin- binding sites are not
detectable in myoblasts. They appear only after myoblasts fuse to form
myotubes and increase gradually to reach a maximal value of 58 fmol/mg of
protein by 8 days in culture. In contrast, [125I]scorpion toxin-binding
sites are first detected during the period of cell fusion and increase
after fusion to reach a maximum by 4 days in culture, well before either
the maximal value of the [3H]saxitoxin binding or the appearance of fully
developed sodium action potentials. Neither [3H]saxitoxin binding nor
[125I] scorpion toxin binding affinity changes during development; they
have values of 1.4 and 62 nM, respectively. These data, and data described
in the companion paper (Baumgold, J., J. B. Parent, and I. Spector (1983)
J. Neurosci. 3: 1004-1013), suggest that sodium channel development
involves two sequential steps: incorporation into the cell membrane of an
immature form of the sodium channel capable of binding scorpion toxin
alone, followed by the acquisition of the ability to bind saxitoxin and
thus to become a mature and functional channel.