Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB263

Poster Communications

Permethrin in low dose reduces excitability in murine peripheral sensory neurons

A. Stojiljkovic1,2, M. H. Stoffel1, J. Balmer1, A. Lampert2

1. Division of Veterinary Anatomy, University of Bern, Bern, Bern, Switzerland. 2. Institute of Physiology, Uniklinik RWTH Aachen, Aachen, Deutschland, Germany.

Pyrethroid insecticides are a family of molecules commonly used for the control of insect pests. The most studied mechanism of pyrethroid action is their binding to the voltage-gated sodium channel (Navs) and the consequent inhibition of inactivation. This leads to neurotoxicity due to disruption of the neuronal conductivity. This mechanism of action works not only in the insect neural system but also in mammals. Nevertheless, the safety of pyrethroid use is ensured by the much higher sensitivity of insect channels to these compounds. Unfortunately, cases of acute pyrethroid intoxication are reported in human and pets, especially cats. The symptoms range from slight burning and stinging sensations to tremor, seizures, coma, and death. Beside heterologous expression systems, so far, only rodent dorsal root ganglia (DRG) in vitro models have been used to study pyrethroid actions (Soderlund 2012), therefore it is not known if species differences in mammal channels, as already described for a variety of insects, could also account for a difference in pyrethroid sensitivity of the Navs. We, therefore, assessed the mechanism of action of permethrin, a type I pyrethroid, on mouse DRGs and plan to compare it with a human in vitro model using human induced pluripotent stem cell (iPSC)-derived nociceptive neurons from healthy individuals. We isolated mouse DRG cells and measured the effect of 1µM permethrin applied in the extracellular bath solution on the action potential (AP) shape and frequency in current clamp. The AP threshold was significantly depolarized (permethrin treated cells (n=15) -34.34 ± 5.85 mV, vehicle-treated control cells (n=14) -41.06 ± 6.93 mV). The time from pulse onset to AP peak was significantly delayed from 33.10 ± 13.56 ms in control to 89.08 ± 58.37 ms in permethrin-treated cells, and the treated cells display a significantly reduced after-hyperpolarization (-63.34 ± 6.40 mV in control cells; -41.52 ± 13.45 in permethrin-treated cells). Supporting these unexpected findings, 1µM Permethrin reduced the firing rate of mouse DRGs, adding additional evidence for a reduction of excitability induced by this pyrethroid in the peripheral nervous system. Our current clamp data of mouse DRG are not easily explained with a simple mechanism of impairment of Nav inactivation. Therefore we hypothesize the contribution of another permethrin action mechanism on DRG cells, either on alternative Nav gating or on other ion channels such as potassium channels, which we aim to follow up. Furthermore, the human iPSC-derived nociceptive neurons model will be used in the future to assess if the same effect can be measured in human cells and possibly reversed using specific channel blockers. The application of permethrin on the human model will for the first time assess possible species differences of pyrethroid mechanisms of action, that can not be verified with the current rodent in vitro models.

Where applicable, experiments conform with Society ethical requirements