Beta-subunit-eliminated eHAP expression (BeHAPe) cells reveal subunit regulation of the cardiac voltage-gated sodium channel.

Voltage-gated sodium (Na) channels drive the upstroke of the action potential and are comprised of a pore-forming α-subunit and regulatory β-subunits. The β-subunits modulate the gating, trafficking, and pharmacology of the α-subunit. These functions are routinely assessed by ectopic expression in heterologous cells. However, currently available expression systems may not capture the full range of these effects since they contain endogenous β-subunits. To better reveal β-subunit functions, we engineered a human cell line devoid of endogenous Na β-subunits and their immediate phylogenetic relatives. This new cell line, β-subunit-eliminated eHAP expression (BeHAPe) cells, were derived from haploid eHAP cells by engineering inactivating mutations in the β-subunits SCN1B, SCN2B, SCN3B, and SCN4B, and other subfamily members MPZ (myelin protein zero(P0)), MPZL1, MPZL2, MPZL3, and JAML. In diploid BeHAPe cells, the cardiac Na α-subunit, Na1.5, was highly sensitive to β-subunit modulation and revealed that each β-subunit and even MPZ imparted unique gating properties. Furthermore, combining β1 and β2 with Na1.5 generated a sodium channel with hybrid properties, distinct from the effects of the individual subunits. Thus, this approach revealed an expanded ability of β-subunits to regulate Na1.5 activity and can be used to improve the characterization of other α/β Na complexes.