Consequences of acute Nav1.1 exposure to deltamethrin

Abstract

Background: Pyrethroid insecticides are the most popular class of insecticides in the world, despite their near-ubiquity, their effects of delaying the onset of inactivation of voltage-gated sodium (Na_v) channels have not been well-evaluated in all the mammalian Na_v isoforms.

Objective: Here we compare the well-studied Na_v1.6 isoforms to the less-understood Na_v1.1 in their responses to acute deltamethrin exposure.

Methods: We used patch-clamp electrophysiology to record sodium currents encoded by either Na_v1.1 or Na_v1.6 channels stably expressed in HEK293 cells. Protocols evaluating both resting and use-dependent modification were employed.

Results: We found that exposure of both isoforms to 10μM deltamethrin significantly potentiated persistent and tail current densities without affecting peak transient current densities, and only Na_v1.1 maintained these significant effects at 1μM deltamethrin. Window currents increased for both as well, and while only Na_v1.6 displayed changes in activation slope and V_1/2 of steady-state inactivation for peak currents, V_1/2 of persistent current activation was hyperpolarized of ∼10mV by deltamethrin in Na_v1.1 cells. Evaluating use-dependence, we found that deltamethrin again potentiated persistent and tail current densities in both isoforms, but only Na_v1.6 demonstrated use-dependent enhancement, indicating the primary deltamethrin-induced effects on Na_v1.1 channels are not use-dependent.

Conclusion: Collectively, these data provide evidence that Na_v1.1 is indeed vulnerable to deltamethrin modification at lower concentrations than Na_v1.6, and this effect is primarily mediated during the resting state.

General significance: These findings identify Na_v1.1 as a novel target of pyrethroid exposure, which has major implications for the etiology of neuropsychiatric disorders associated with loss of Na_v1.1-expressing inhibitory neurons.

Fig. 1

Representative traces of HEK-Na_v1.1 (A) or HEK-Na_v1.6 (B) cells in DMSO or deltamethrin-treated conditions in response to an evoked step-wise protocol (schematic under traces). With DMSO in black, Panels C and D depict a current-voltage relationship for Na_v1.1 and Na_v1.6, respectively, showing deltamethrin treatment in blue for Na_v1.1 and green for Na_v1.6. Summary bar graphs comparing peak current densities at −10 mV for all three concentrations are shown below the I–V graphs. Voltage-dependencies of activation and steady-state inactivation are depicted for Na_v1.1 (E) and Na_v1.6 (F); control curves are represented with dashed lines. Window currents are depicted where activation and steady-state inactivation curves overlap, which is indicated with shaded areas—gray for DMSO and colors for deltamethrin. Error bars indicate SEM. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Representative traces of persistent currents and tail currents (insets) are shown for HEK-Na_v1.1 cells (A) and HEK-Na_v1.6 cells (B) with deltamethrin shown in blue and green, respectively. Current-voltage relationships are shown for Na_v1.1 and Na_v1.6 persistent currents (C, D, respectively) and for Na_v1.1 and Na_v1.6 tail currents (E, F, respectively). Circles represent 10 μM or 0.1% final DMSO concentration; triangles represent 1 μM or 0.01% final DMSO concentration, and diamonds indicate 0.1 μM or 0.001% final DMSO concentration. Error bars indicate SEM. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Current-voltage relationship for Na_v1.1 (A) and Na_v1.6 (B) depicting DMSO control peak currents (black squares) and deltamethrin persistent currents (colored circles). Concentration-dependent effect of deltamethrin as percentage of deltamethrin modified channels shown in C, with Na_v1.1 represented in blue and Na_v1.6 in green. Error bars indicate SEM. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Representative traces of: A) Use-dependent stimulation protocols, B) HEK-Na_v1.1 cells treated with DMSO (black) or 10 μM deltamethrin (blue), C) HEK-Na_v1.6 cells treated with DMSO (black) or 10 μM deltamethrin (green). Below traces are summary bar graphs for both stimulation frequencies representing: D) Peak current density, E) Tail current density, F) Peak current density modification, G) Tail current density modification, H) Persistent current density, I) Fraction of available current, J) Peak current modification, K) Total charge. Error bars indicate SEM. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)