Human and rat Na(v)1.3 voltage-gated sodium channels differ in inactivation properties and sensitivity to the pyrethroid insecticide tefluthrin

Voltage-gated sodium channels are important sites for the neurotoxic actions of pyrethroid insecticides in mammals. The pore-forming alpha subunits of mammalian sodium channels are encoded by a family of 9 genes, designated Na(v)1.1-Na(v)1.9. Native sodium channels in the adult central nervous system (CNS) are heterotrimeric complexes of one of these 9 alpha subunits and two auxiliary (beta) subunits. Here we compare the functional properties and pyrethroid sensitivity of the rat and human Na(v)1.3 isoforms, which are abundantly expressed in the developing CNS. Coexpression of the rat Na(v)1.3 and human Na(v)1.3 alpha subunits in combination with their conspecific beta 1 and beta 2 subunits in Xenopus laevis oocytes gave channels with markedly different inactivation properties and sensitivities to the pyrethroid insecticide tefluthrin. Rat Na(v)1.3 channels inactivated more slowly than human Na(v)1.3 channels during a depolarizing pulse. The rat and human channels also differed in their voltage dependence of steady-state inactivation. Exposure of rat and human Na(v)1.3 channels to 100 mu M tefluthrin in the resting state produced populations of channels that activated, inactivated and deactivated more slowly than unmodified channels. For both rat and human channels, application of trains of depolarizing prepulses enhanced the extent of tefluthrin modification approximately twofold; this result implies that tefluthrin may bind to both the resting and open states of the channel. Modification of rat Na(v)1.3 channels by 100 mu M tefluthrin was fourfold greater than that measured in parallel assays with human Na(v)1.3 channels. Human Na(v)1.3 channels were also less sensitive to tefluthrin than rat Na(v)1.2 channels, which are considered to be relatively insensitive to pyrethroids. These data provide the first direct comparison of the functional and pharmacological properties of orthologous rat and human sodium channels and demonstrate that orthologous channels with a high degree of amino acid sequence conservation differ in both their functional properties and their sensitivities to pyrethroid insecticides. (C) 2008 Elsevier Inc. All rights reserved.