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Science 18 July 1986:
Vol. 233. no. 4761, pp. 361 - 364
DOI: 10.1126/science.2425432
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Articles

Science, Vol 233, Issue 4761, 361-364
Copyright © 1986 by American Association for the Advancement of Science

articles

Functional differences between two classes of sodium channels in developing rat skeletal muscle

RE Weiss and R Horn

Excitability is generated in developing skeletal muscle by the incorporation of sodium-selective ion channels into the surface membrane. Whole-cell and patch voltage-clamp recording from myotubes and their embryologic precursors, myoblasts, indicated that voltage-activated sodium current in myoblasts was more resistant to block by tetrodotoxin (TTX) than that in myotubes. Single-channel recording from both cell types showed two classes of sodium channels. One class had a lower single-channel conductance, activated at more hyperpolarized voltages, and was more resistant to TTX than the other. The proportion of TTX-resistant to TTX-sensitive sodium channels was higher in myoblasts than in myotubes. Thus, the difference in TTX sensitivity between myoblasts and myotubes can be explained by a difference in the proportion of the two classes of sodium channels. In addition, the lower conductance of TTX-resistant channels provides insight into the relationship between the TTX binding site and the external mouth of the sodium channel.


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