Primary structure and functional expression of the beta 1 subunit of the rat brain sodium channel

Abstract

Voltage-sensitive sodium channels are responsible for the initiation and propagation of the action potential and therefore are important for neuronal excitability. Complementary DNA clones encoding the beta 1 subunit of the rat brain sodium channel were isolated by a combination of polymerase chain reaction and library screening techniques. The deduced primary structure indicates that the beta 1 subunit is a 22,851-dalton protein that contains a single putative transmembrane domain and four potential extracellular N-linked glycosylation sites, consistent with biochemical data. Northern blot analysis reveals a 1,400-nucleotide messenger RNA in rat brain, heart, skeletal muscle, and spinal cord. Coexpression of beta 1 subunits with alpha subunits increases the size of the peak sodium current, accelerates its inactivation, and shifts the voltage dependence of inactivation to more negative membrane potentials. These results indicate that the beta 1 subunit is crucial in the assembly, expression, and functional modulation of the heterotrimeric complex of the rat brain sodium channel.

Modulatory Proteins Can Rescue a Trafficking Defective Epileptogenic Nav1.1 Na+Channel Mutant

“…␤ subunits can increase Na ϩ current density and membrane insertion of wild-type ␣ subunits in some expression systems (Isom et al, 1992(Isom et al, , 1995 but not in others (Morgan et al, 2000;Qu et al, 2001;Yu et al, 2003). Thus, in some conditions, ␤ subunits can act as chaperones also for wild-type ␣ subunits, but in our experimental conditions, they did not have any significant effects.…”

“…We numbered ␤1 protein sequence starting with the initial methionine, thus including the leader sequence identified by Isom et al (1992). To express with the same plasmid both the protein of interest and cyan fluorescent protein (CFP) as reporter, the cDNAs were subcloned into the bicistronic mammalian expression vector pIRES-CFP (Clontech).…”

Sodium channel Scn1b null mice exhibit prolonged QT and RR intervals

“…Coexpression of β1 with TTX-S sodium channel α subunits in heterologous systems in vitro results in increased I Na , increased rates of channel activation and inactivation, and shifts in the voltage-dependence of activation and inactivation [4,34]. Interestingly, results from acutely isolated Scn1b null hippocampal and cerebellar neurons, which express primarily TTX-S channels, showed none of these effects [12,26], suggesting that the physiological roles of β1 may be cell type specific and, importantly, that heterologous expression systems cannot mimic the situation in neurons.…”

“…Mutations in SCN5A encoding Na v 1.5, the major cardiac channel, result in Long QT and Brugada syndromes [1]. Sodium channels are heterotrimers, composed of a single, pore-forming α subunit and two β subunits [3]: a noncovalently linked subunit (β1 or β3) [4,5] and a disulfide-linked subunit (β2 or β4) [6,7]. β subunits are multi-functional molecules that regulate channel cell-surface expression levels and modulate channel function, affecting channel kinetics and voltage-dependence in vitro [8].…”

A molecular basis for gating mode transitions in human skeletal muscle Na+ channels

“…It has been speculated that a modulatory factor encoded in the low molecular weight mRNA may be an enzyme or an accessory peptide such as a p subunit [3]. A recent report indicated that a recombinant /3] subunit from rat brain increased Na+ current and induced fast inactivation of rat brain II Na' channel a: subunits expressed in oocytes [4]. The observed changes in rat brain sodium current upon co-expression with a /?, subunit may have arisen from an increase in the number of expressed channels or possibly by a change in channel gating, however, the precise mechanism has not been determined.…”