Sigma-1 Receptor Agonists Directly Inhibit Na_V1.2/1.4 Channels

(+)-SKF 10047 (N-allyl-normetazocine) is a prototypic and specific sigma-1 receptor agonist that has been used extensively to study the function of sigma-1 receptors. (+)-SKF 10047 inhibits K⁺, Na⁺ and Ca2+ channels via sigma-1 receptor activation. We found that (+)-SKF 10047 inhibited Na_V1.2 and Na_V1.4 channels independently of sigma-1 receptor activation. (+)-SKF 10047 equally inhibited Na_V1.2/1.4 channel currents in HEK293T cells with abundant sigma-1 receptor expression and in COS-7 cells, which barely express sigma-1 receptors. The sigma-1 receptor antagonists BD 1063,BD 1047 and NE-100 did not block the inhibitory effects of (+)-SKF-10047. Blocking of the PKA, PKC and G-protein pathways did not affect (+)-SKF 10047 inhibition of Na_V1.2 channel currents. The sigma-1 receptor agonists Dextromethorphan (DM) and1,3-di-o-tolyl-guanidine (DTG) also inhibited Na_V1.2 currents through a sigma-1 receptor-independent pathway. The (+)-SKF 10047 inhibition of Na_V1.2 currents was use- and frequency-dependent. Point mutations demonstrated the importance of Phe¹⁷⁶⁴ and Tyr¹⁷⁷¹ in the IV-segment 6 domain of the Na_V1.2 channel and Phe¹⁵⁷⁹ in the Na_V1.4 channel for (+)-SKF 10047 inhibition. In conclusion, our results suggest that sigma-1 receptor agonists directly inhibit Na_V1.2/1.4 channels and that these interactions should be given special attention for future sigma-1 receptor function studies.