The importance of serine 161 in the sodium channel β3 subunit for modulation of Na V 1.2 gating

Voltage-gated sodium (Na) channels contribute to the regulation of cellular excitability due to their role in the generation and propagation of action potentials. They are composed of a pore-forming α subunit and are modulated by at least two of four distinct β subunits (β1–4). Recent studies have implicated a role for the intracellular domain of β subunits in modulating Na channel gating and trafficking. In β3, the intracellular domain contains a serine residue at position 161 that is replaced by an alanine in β1. In this study, we have probed the functional importance of β3S161 for modulating Na channel gating. Wild-type β3 and point mutations β3S161A or β3S161E were individually co-expressed in HEK 293 cells stably expressing human Na v 1.2. WTβ3 expression increased Na current density, shifted steady-state inactivation in a depolarized direction, and accelerated the kinetics of recovery from inactivation of the Na current. Analogous effects were observed with β3S161E co-expression. In contrast, β3S161A abolished the shifts in steady-state inactivation and recovery from inactivation of the Na current, but did increase Na current density. Immunocytochemistry and Western blot experiments demonstrate membrane expression of WTβ3, β3S161E, and β3S161A, suggesting that the differences in Na channel gating were not due to disruptions in β subunit trafficking. These studies suggest that modification of β3S161 may be important in modulating Na-channel gating.