Regulation of Na_v1.6 and Na_v1.8 peripheral nerve Na⁺ channels by auxiliary β-subunits

Regulation of Na_v1.6 and Na_v1.8 peripheral nerve Na⁺ channels by auxiliary β-subunits. J Neurophysiol 106: 608-619, 2011. First published May 11, 2011; doi:10.1152/jn.00107.2011-Voltage-gated Na⁺ (Na_v) channels are composed of a pore-forming -subunit and one or more auxiliary β-subunits. The present study investigated the regulation by the β-subunit of two Na⁺ channels (Na_v1.6 and Na_v1.8) expressed in dorsal root ganglion (DRG) neurons. Single cell RT-PCR was used to show that Na_v1.8, Na_v1.6, and β₁-β₃ subunits were widely expressed in individually harvested small-diameter DRG neurons. Coexpression experiments were used to assess the regulation of Na_v1.6 and Na_v1.8 by β-subunits. The β₁-subunit induced a 2.3-fold increase in Na⁺ current density and hyperpolarizing shifts in the activation (β₄ mV) and steady-state inactivation (-4.7 mV) of heterologously expressed Na_v1.8 channels. The β₄-subunit caused more pronounced shifts in activation (-16.7 mV) and inactivation (-9.3 mV) but did not alter the current density of cells expressing Na_v1.8 channels. The β₃-subunit did not alter Na_v1.8 gating but significantly reduced the current density by 31%. This contrasted with Na_v1.6, where the β-subunits were relatively weak regulators of channel function. One notable exception was the β₄-subunit, which induced a hyperpolarizing shift in activation (-7.6 mV) but no change in the inactivation or current density of Na_v1.6. The β-subunits differentially regulated the expression and gating of Na_v1.8 and Na_v1.6. To further investigate the underlying regulatory mechanism, β-subunit chimeras containing portions of the strongly regulating β₁-subunit and the weakly regulating β₂-subunit were generated. Chimeras retaining the COOH-terminal domain of the β₁-subunit produced hyperpolarizing shifts in gating and increased the current density of Na_v1.8, similar to that observed for wild-type β₁-subunits. The intracellular COOH-terminal domain of the β₁-subunit appeared to play an essential role in the regulation of Na_v1.8 expression and gating.