Modulation of sodium-channel mRNA levels in rat skeletal muscle.

Abstract

Action potentials in many types of excitable cells result from changes in permeability to Na ions. Although these permeability changes in nerve and muscle are mediated by voltage-gated Na channels that are functionally similar, we found that the Na-channel gene expressed in skeletal muscle is different from the genes coding for two Na channels (type I and type II) in brain. Despite the structural differences between muscle and brain Na-channel genes, a cDNA clone derived from rat brain hybridizes to skeletal muscle Na-channel mRNA of =9.5 kilobases. We used this cDNA probe to measure changes in Na-channel mRNA levels in skeletal muscle during development and following denervation. By blot hybridization analysis of electrophoretically fractionated RNA, we found that Na-channel mRNA can be detected as early as embryonic day 17 and that mRNA levels increase 2-fold between birth and postnatal day 35. Denervation of adult muscle causes a further 2-to 3-fold increase in muscle Na-channel mRNA levels, suggesting that expression of Na-channel genes in fast-twitch muscle may be regulated by the state of innervation.Voltage-gated Na channels control the rapid changes in Na permeability responsible for the generation of an action potential in both nerve and muscle (1). Many functional properties of brain and skeletal muscle Na channels are similar (2), suggesting that the structure of the Na-channel protein is highly conserved in these tissues. Recent biochemical studies of Na channels isolated from rat brain and rat and rabbit skeletal muscle support this concept (3, 4). However, Na channels in brain and muscle also exhibit significant differences. Even within the same species, Na channels are immunologically distinct (5, 6) and exhibit differential sensitivity to several neurotoxins (7, 8).In addition to differences between tissues, Na channels within a single tissue may also exhibit diversity. Messenger RNAs coding for two different Na channels have been identified in rat brain on the basis of sequence analysis of distinct complementary DNA (cDNA) clones (9). There is also evidence for multiple isotypes of the Na channel in skeletal muscle. Mature muscle expresses Na channels sensitive to nanomolar concentrations of tetrodotoxin (lTx), but denervated and embryonic muscle synthesize a TTxinsensitive form of the channel (10-16). Channels in the surface membrane and channels in the transverse (T)-tubular system of mature muscle are antigenically distinct and exhibit differential sensitivity to Yfx derivatives and to polypeptide toxins (17, 18). Unfortunately, no information is currently available concerning the primary sequence of Na channels expressed in mammalian skeletal muscle. Therefore, the structural differences between these muscle channels, and the mechanisms that control their differential expression, remain completely unknown.In this paper we show that extensor digitorum longus (e.d.l.) muscle does not contain detectable levels of rat brain Na-channel gene I or gene II transcripts. Nonetheless, a cDNA en...

Differential regulation of neuronal sodium channel expression by endogenous and exogenous tyrosine kinase receptors expressed in rat pheochromocytoma cells

“…In addition, because it has been postulated that the transient nature of the cellular responses to EGF receptor activation may be the basis for the differences in the actions of EGF and NGF (Heasley and Johnson, 1992;Qiu and Green, 1992), Na channel mRNA levels were analyzed in cells treated over a time course of l-7 d. Northern blot analysis was carried out as in our previous studies (Ginty et al, 1992;Fanger et al, 1993) using a 32P-labeled antisense probe that corresponds to a coding region highly conserved among Na channel genes (Mandel et al, 1988) and recognizes multiple types of Na channel mRNA (Cooperman et al, 1987;Sills et al, 1989). In response to NGF, there was a clearly detectable increase in Na channel mRNA by the earliest time assayed (24 hr), with a steady increase in Na channel mRNA throughout the time period investigated (Fig.…”

Embryonic and larval expression of zebrafish voltage‐gated sodium channel α‐subunit genes

“…In mammals, SCN4A is expressed almost exclusively in skeletal muscle (Trimmer et al, 1989). Furthermore, SCN4A expression occurs embryonically during maturation of neuromuscular transmission (Cooperman et al, 1987;Trimmer et al, 1990). Similar to the scn1La duplicated genes, scn4aa and scn4ab are expressed in nonoverlapping patterns.…”

Identification of PN1, a predominant voltage-dependent sodium channel expressed principally in peripheral neurons

“…Total cellular RNA was isolated from PC12 cells as described in Cathala et al (21) and from adult Sprague-Dawley rat brain, spinal cord, superior cervical ganglion, dorsal root ganglion, skeletal muscle, cardiac muscle, and adrenal gland using the standard method of Chirgwin et al (25). Northern blot analysis was performed according to Toledo-Aral et al (18) using 32 P-UTP-labeled antisense RNA probes generated from the following linearized templates: pPC12-1, pRB211 (26), and pIB15 (cyclophilin; ref. 27).…”