Isoform-specific effects of the β2 subunit on voltage-gated sodium channel gating

Voltage-gated sodium channels (Na-v) are complex glycoproteins comprised of an alpha subunit and often one to several beta subunits. We have shown that sialic acid residues linked to Na-v alpha and beta(1) subunits alter channel gating. To determine whether beta(2)-linked sialic acids similarly impact Na-v gating, we co-expressed beta(2) with Na(v)1.5 or Na(v)1.2 in Pro5 (complete sialylation) and in Lec2 (essentially no sialylation) cells. beta(2) sialic acids caused a significant hyperpolarizing shift in Na(v)1.5 voltage-dependent gating, thus describing for the first time an effect of beta(2) on Na(v)1.5 gating. In contrast, beta(2) caused a sialic acid-independent depolarizing shift in Na(v)1.2 gating. A deglycosylated mutant, beta(2-Delta N), had no effect on Na(v)1.5 gating, indicating further the impact of beta(2) N-linked sialic acids on Na(v)1.5 gating. Conversely, beta(2-Delta N) modulated Na(v)1.2 gating virtually identically to beta(2), confirming that beta(2) N-linked sugars have no impact on Na(v)1.2 gating. Thus, beta(2) modulates Na-v gating through multiple mechanisms possibly determined by the associated alpha subunit. beta(1) and beta(2) were expressed together with Na(v)1.5 or Na(v)1.2 in Pro5 and Lec2 cells. Together beta(1) and beta(2) produced a significantly larger sialic acid-dependent hyperpolarizing shift in Nav1.5 gating. Under fully sialylating conditions, the Na(v)1.2(.)beta(.)(1)beta(2) complex behaved like Na(v)1.2 alone. When sialylation was reduced, only the sialic acid-independent depolarizing effects of beta(2) on Na(v)1.2 gating were apparent. Thus, the varied effects of beta(1) and beta(2) on Na(v)1.5 and Na(v)1.2 gating are apparently synergistic and highlight the complex manner, through subunit-and sugar-dependent mechanisms, by which Na-v activity is modulated.