Role of the Local Anesthetic Receptor in the State-Dependent Inhibition of Voltage-Gated Sodium Channels by the Insecticide Metaflumizone

Abstract

Sodium channel inhibitor (SCI) insecticides selectively target voltage-gated sodium (Na v ) channels in the slow-inactivated state by binding at or near the local anesthetic receptor within the sodium channel pore. Metaflumizone is a new insecticide for the treatment of fleas on domesticated pets and has recently been reported to block insect sodium channels in the slow-inactivated state, thereby implying that it is also a member of the SCI class. Using the two-electrode voltage-clamp technique, we examined metaflumizone inhibition of rat Na v 1.4 sodium channels expressed in Xenopus laevis oocytes. Metaflumizone selectively inhibited Na v 1.4 channels at potentials that promoted slow inactivation and shifted the voltage dependence of slow inactivation in the direction of hyperpolarization. Metaflumizone perfusion at a hyperpolarized holding potential also shifted the conductance-voltage curve for activation in the direction of depolarization and antagonized use-dependent lidocaine inhibition of fast-inactivated sodium channels, actions not previously observed with other SCI insecticides. We expressed mutated Na v 1.4/F1579A and Na v 1.4/Y1586A channels to investigate whether metaflumizone shares the domain IV segment S6 (DIV-S6) binding determinants identified for other SCI insecticides. Consistent with previous investigations of SCI insecticides on rat Na v 1.4 channels, the F1579A mutation reduced sensitivity to block by metaflumizone, whereas the Y1586A mutation paradoxically increased the sensitivity to metaflumizone. We conclude that metaflumizone selectively inhibits slow-inactivated Na v 1.4 channels and shares DIV-S6 binding determinants with other SCI insecticides and therapeutic drugs. However, our results suggest that metaflumizone interacts with resting and fast-inactivated channels in a manner that is distinct from other compounds in this insecticide class.

Inhibition of Nav1.7 channels by methyl eugenol as a mechanism underlying its antinociceptive and anesthetic actions

“…Through its rapid binding to open channels and stabilization of a nonconducting state, methyl eugenol can produce greater and faster use-dependent inhibition of Na + current and slow the kinetics of recovery of channels in the inactivated state [40] . Methyl eugenol rapidly reaches a steady-state level in a use-dependent manner ( Figure 3B, 3C), similar to the usedependency evoked by lidocaine on Nav1.4 [41,42] , Nav1.7 [43,44] , Nav1.5 [45] , and Nav1.8 [43] . This similarity in use-dependency between methyl eugenol and lidocaine suggests that methyl eugenol also binds to open and/or inactivated states of the channel to produce a greater use-dependence [40] .…”

Compound-specific effects of mutations at Val787 in DII-S6 of Nav1.4 sodium channels on the action of sodium channel inhibitor insecticides

“…The rat skeletal muscle sodium channel (Na v 1.4) was chosen for the present study because it is a well-defined model system for studying the actions of SCI insecticides on cloned mammalian sodium channels (Silver and Soderlund, 2005b, 2007; von Stein and Soderlund, 2012). The use of Na v 1.4 also ensured that mutations at Val787 yielded the expected residue-specific effects on slow inactivation that have been reported elsewhere (O’Reilly et al ., 2001).…”

“…They have no effect on channels in the resting state but disrupt channel function through a selective interaction with channels in the non-conducting slow-inactivated state (Salgado, 1992; Lapied et al ., 2001; Zhao et al ., 2003; Silver and Soderlund, 2005b; von Stein and Soderlund, 2012). However, previous studies provide indirect evidence that some SCIs may also interact with other sodium channel states.…”

“…Experiments with crayfish axons showed that inhibition of sodium channels by an experimental SCI insecticide (RH-1211) was not disrupted by progressive proteolytic removal of slow and fast inactivation by intracellular perfusion of trypsin and N -bromoacetamide, respectively (Salgado, 1992). Furthermore, metaflumizone differed from other SCI insecticides in its ability to antagonize the inhibition of Na v 1.4 sodium channels by the local anesthetic lidocaine under experimental conditions that promoted lidocaine binding to fast-inactivated channels but did not cause insecticide inhibition (von Stein and Soderlund, 2012). These results not only suggest that metaflumizone may bind to fast-inactivated channels without inhibiting them but also imply a fundamental difference in the state-dependent action of metaflumizone compared to other SCI insecticides.…”

“…Residues in domain IV-S6, particularly Phe1579 and Tyr1586 (rat Na v 1.4 numbering) appear to be essential for state-dependent inhibition by SCI drugs. Inhibition of slow-inactivated Na v 1.4 channels by SCI insecticides is also modulated by mutations at Phe1579 and Tyr1586 (Silver and Soderlund, 2007; von Stein and Soderlund, 2012). These findings are consistent with the hypothesis that SCI insecticides bind selectively to slow-inactivated sodium channels at or near the LA receptor.…”