Low potency inhibition of NaV1.7 by externally applied QX-314 via a depolarizing shift in the voltage-dependence of activation

• Published in: European journal of pharmacology 2022-06, Vol.925, p.175013-175013, Article 175013
• Main Authors: Klasfauseweh, Tabea, Israel, Mathilde R., Ragnarsson, Lotten, Cox, James J., Durek, Thomas, Carter, David A., Leffler, Andreas, Vetter, Irina, Deuis, Jennifer R.
• Format: Article
• Language: English
• Subjects: Lidocaine; Local anesthetic; NaV1.7; Pain; QX-314; Voltage-gated sodium channel
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/j.ejphar.2022.175013

QX-314 is a quaternary permanently charged lidocaine derivative that inhibits voltage-gated sodium channels (NaV). As it is membrane impermeable, it is generally considered that QX-314 applied externally is inactive, unless it can gain access to the internal local anesthetic binding site via another entry pathway. Here, we characterized the electrophysiological effects of QX-314 on NaV1.7 heterologously expressed in HEK293 cells, and found that at high concentrations, external QX-314 inhibited NaV1.7 current (IC50 2.0 ± 0.3 mM) and shifted the voltage-dependence to more depolarized potentials (ΔV50 +10.6 mV). Unlike lidocaine, the activity of external QX-314 was not state- or use-dependent. The effect of externally applied QX-314 on NaV1.7 channel biophysics differed to that of internally applied QX-314, suggesting QX-314 has an additional externally accessible site of action. In line with this hypothesis, disruption of the local anesthetic binding site in a [F1748A]NaV1.7 mutant reduced the potency of lidocaine by 40-fold, but had no effect on the potency or activity of externally applied QX-314. Therefore, we conclude, using an expression system where QX-314 was unable to cross the membrane, that externally applied QX-314 is able to inhibit NaV1.7 peak current at low millimolar concentrations. [Display omitted] •QX-314 is a permanently charged membrane impermeable derivative of lidocaine•QX-314 is unable to cross the membrane of HEK293 cells expressing NaV1.7•When applied externally, QX-314 can inhibit NaV1.7 current (IC50 = 2.0 mM)•The effect of internal and external QX-314 on NaV1.7 biophysics are distinct•We conclude QX-314 is active externally at high concentrations