Molecular determinant of low-voltage dependence of human Na_v1.7 inactivation revealed by efficacy-based Na_v1.7 selective inhibitor.

Abstract

Na_v1.7 is a voltage-gated sodium channel (VGSC) subtype predominantly expressed in sensory neurons, amplifying threshold currents. Here, we identify that Uvarigranol D (UGD) suppresses human (h) Na_v1.7 with a much greater maximal inhibition than other VGSC subtypes, despite having similar apparent affinities. We demonstrate that Thr¹³⁹⁸ determines the greater inhibitory efficacy of UGD, the leftward shift in voltage-dependence and faster inactivation kinetics of hNa_v1.7. UGD binds to the inactivated state, with Gln³⁶⁰, Ile³⁹⁴, Lys¹³⁹⁵, Phe¹⁷³⁷, and Tyr¹⁷⁴⁴ being critically involved. Moreover, while UGD suppresses action potentials in both rat dorsal root ganglion neurons and human induced pluripotent stem cell-derived cardiomyocytes, its ~60-fold greater sensitivity in neurons demonstrates that differences in maximal inhibition can translate into functional selectivity across excitable cells. We conclude that Thr¹³⁹⁸ is critical to the unique function of hNa_v1.7 as a threshold current generator, and the lower voltage-dependence can be exploited for developing selective Na_v1.7 inhibitors.