SkM2, a Na+ channel cDNA clone from denervated skeletal muscle, encodes a tetrodotoxin-insensitive Na+ channel

• Published in: Molecular pharmacology Vol. 39; no. 5; p. 604
• Main Authors: White, M M, Chen, L Q, Kleinfield, R, Kallen, R G, Barchi, R L
• Format: Journal Article
• Language: English
• Published: United States 01-05-1991
• Subjects: Animals; Base Sequence; Cloning, Molecular; Conotoxins; DNA - genetics; Female; Molecular Sequence Data; Muscles - innervation; Muscles - physiology; Muscles - ultrastructure; Myocardium - metabolism; Oocytes - physiology; Peptides, Cyclic - pharmacology; RNA, Messenger - genetics; RNA, Messenger - metabolism; Sodium Channels - drug effects; Sodium Channels - genetics; Tetrodotoxin - pharmacology; Xenopus laevis
• ISSN: 0026-895X

Approximately one third of the Na+ channels expressed in denervated or developing skeletal muscle are tetrodotoxin (TTX) insensitive, with a Kd for channel blockade of approximately 1 microM, similar to that found for cardiac Na+ channels. We have recently reported the cloning of a putative Na+ channel subtype that is characteristic of denervated and developing skeletal muscle (SkM2), the deduced amino acid sequence of which is identical to that of a Na+ channel cDNA isolated from heart. We have now examined the functional properties of SkM2 Na+ channels after expression in Xenopus oocytes. We found that the efficiency of expression of constructs containing the SkM2 clone was strongly dependent on the amount of 5'-untranslated region (5'UTR) included. Constructs containing a 206-nucleotide 5'UTR were expressed poorly, whereas constructs from which most of the 5'UTR was removed were expressed well. The channels showed rapid voltage-dependent activation and inactivation. In addition, SkM2 Na+ channels were insensitive to low concentrations of TTX but were ultimately blocked by this toxin, with a Kd of 1.9 microM. The TTX block exhibited use dependence. Finally, SkM2 Na+ channels were not blocked by 100 nM mu-conotoxin, which blocks Na+ channels in innervated skeletal muscle in the low nanomolar concentration range. These data indicate that SkM2 Na+ channels are the TTX-insensitive Na+ channels found in denervated or developing skeletal muscle and are identical to the TTX-insensitive Na+ channels from heart.