Effects of the β1 auxiliary subunit on modification of Rat Nav1.6 sodium channels expressed in HEK293 cells by the pyrethroid insecticides tefluthrin and deltamethrin

Abstract

We expressed rat Nav1.6 sodium channels with or without the rat β1 subunit in human embryonic kidney (HEK293) cells and evaluated the effects of the pyrethroid insecticides tefluthrin and deltamethrin on whole-cell sodium currents. In assays with the Nav1.6 α subunit alone, both pyrethroids prolonged channel inactivation and deactivation and shifted the voltage dependence of channel activation and steady-state inactivation toward hyperpolarization. Maximal shifts in activation were ~18 mV for tefluthrin and ~24 mV for deltamethrin. These compounds also caused hyperpolarizing shifts of ~10–14 mV in the voltage dependence of steady-state inactivation and increased in the fraction of sodium current that was resistant to inactivation. The effects of pyrethroids on the voltage-dependent gating greatly increased the size of sodium window currents compared to unmodified channels; modified channels exhibited increased probability of spontaneous opening at membrane potentials more negative than the normal threshold for channel activation and incomplete channel inactivation. Coexpression of Nav1.6 with the β1 subunit had no effect on the kinetic behavior of pyrethroid-modified channels but had divergent effects on the voltage-dependent gating of tefluthrin- or deltamethrin-modified channels, increasing the size of tefluthrin-induced window currents but decreasing the size of corresponding deltamethrin-induced currents. Unexpectedly, the β1 subunit did not confer sensitivity to use-dependent channel modification by either tefluthrin or deltamethrin. We conclude from these results that functional reconstitution of channels in vitro requires careful attention to the subunit composition of channel complexes to ensure that channels in vitro are faithful functional and pharmacological models of channels in neurons.

Consequences of acute Na v 1.1 exposure to deltamethrin

“…Our values and outcomes for these parameters in Na v 1.6 differ somewhat from other studies’ findings (Tan and Soderlund, 2010; He and Soderlund, 2011; McCavera and Soderlund, 2012), a disparity that might be attributed to species differences. Compared with HEK293 cells prepared similarly to ours with expression of rat Na v 1.6, our human Na v 1.6 appears to be less sensitive to deltamethrin modification than the rat Na v 1.6 used in the same HEK293 expression system (He and Soderlund, 2015). Without varying methods of expression, it is then likely that the differences seen between rat and human Na v 1.6 stem from differences between the two species.…”

Functional reconstitution of rat Na v 1.6 sodium channels in vitro for studies of pyrethroid action

“…We explored the impact of the auxiliary β subunits on Na v 1.6 channel modification by tefluthrin and deltamethrin by comparing the action of these insecticides on Na v 1.6, Na v 1.6+β1, or Na v 1.6+β1+β2 channels (He and Soderlund, 2011; He and Soderlund, 2016) Coexpression with β subunits exerted opposite effects on the shifts in voltage-dependent gating of Na v 1.6 channels caused by tefluthrin and deltamethrin. The β1 subunit increased the magnitude of the tefluthrin-dependent hyperpolarizing shifts in both activation (Fig.…”

“…The importance of use-dependent channel modification in the action of pyrethroids on both insect and mammalian channels expressed in Xenopus oocytes led us to examine use-dependent modification of rat Na v 1.6 channels expressed in HEK293 cells and the impact of coexpression with the β1 and β2 subunits on use-dependent modification (He and Soderlund, 2011; He and Soderlund, 2016). In the HEK293 cell system the action of deltamethrin was enhanced by more than two-fold by repetitive depolarization, whereas the action of tefluthrin was unaffected (Fig.…”

“…Effect of coexpression with β subunits on the modification of the voltage-dependent gating of rat Na v 1.6 channels expressed in HEK293 cells by tefluthrin and deltamethrin (redrawn from data in He and Soderlund, 2011; He and Soderlund, 2016). (A) Effect of coexpression with β subunits on the magnitude of the shift in V 0.5 values for Na v 1.6 sodium channel activation caused by tefluthrin (100 µM) or deltamethrin (10 µM).…”

“…Resting and use-dependent modification of rat Na v 1.6 sodium channels expressed in HEK293 cells by pyrethroids (redrawn from data in He and Soderlund, 2011; He and Soderlund, 2016). (A) Effects of repeated 5-ms depolarizing prepulses delivered at 20 Hz on the extent of modification of sodium channels in HEK293 cells expressing Na v 1.6+β1+β2 sodium channels by tefluthrin or deltamethrin.…”