EXPRESSION OF THE SODIUM CHANNEL-BETA(1) SUBUNIT IN RAT SKELETAL-MUSCLE IS SELECTIVELY ASSOCIATED WITH THE TETRODOTOXIN-SENSITIVE ALPHA-SUBUNIT ISOFORM

Transcripts homologous to the rat brain sodium channel beta subunit (b eta1) are prominently expressed in both innervated and denervated adul t skeletal muscle and in heart, but not in neonatal skeletal or cardia c muscle. Regulation of beta1 mRNA expression closely parallels that o f SkM1 alpha during development, after denervation in adult muscle, an d in primary muscle culture, but does not follow SkM2 expression under any condition examined. In oocytes, beta1 interacts functionally with SkM1 to modulate the abnormally slow inactivation kinetics observed w ith this alpha subunit expressed alone. We conclude that a common beta 1 subunit is expressed in skeletal muscle, heart, and brain and that i n skeletal muscle, this subunit is specifically associated with the Sk M1, rather than the SkM2, sodium channel isoform.