The voltage-gated Na⁺ channel Na_v1.8 contains an ER-retention/retrieval signal antagonized by the 3 subunit

Voltage-gated Na⁺ channel (Na_v) 1.8 contributes to the majority of the Na⁺ current that underlies the depolarizing phase of action potentials. Na_v1.8 is mainly distributed intracellularly and its current amplitude can be enhanced by the 3 subunit. However, little is known about the mechanisms underlying its intracellular retention and the effects mediated by the 3 subunit. Here, we show that the 3 subunit promotes surface expression of Na_v1.8 by masking its endoplasmic reticulum (ER)-retention/retrieval signal. The RRR motif in the first intracellular loop of Na_v1.8 is responsible for retaining Na_v1.8 in the ER and restricting its surface expression. The 3 subunit facilitates surface expression of Na_v1.8. The intracellular C-terminus of the 3 subunit interacts with the first intracellular loop of Na_v1.8 and masks the ER-retention/retrieval signal. Mutation of the RRR motif results in a significant increase in surface expression of Na_v1.8 and abolishes the 3-subunit-mediated effects. Thus, the 3 subunit regulates surface expression of Na_v1.8 by antagonizing its ER-retention/retrieval signal. These results reveal a novel mechanism for the effect of the Na⁺ channel subunits on the subunits.