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 (beta1) are prominently expressed in both innervated and denervated adult skeletal muscle and in heart, but not in neonatal skeletal or cardiac muscle. Regulation of beta1 mRNA expression closely parallels that of SkM1 alpha during development, after denervation in adult muscle, and 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 with this alpha subunit expressed alone. We conclude that a common beta1 subunit is expressed in skeletal muscle, heart, and brain and that in skeletal muscle, this subunit is specifically associated with the SkM1, rather than the SkM2, sodium channel isoform.