Pyrethroid insecticides: Potent, stereospecific enhancers of mouse brain sodium channel activation

Abstract

Deltamethrin and NRDC 157, pyrethroid insecticides that produce different poisoning syndromes in mammals, enhanced veratridine-dependent, sodium channel-mediated 22Na + uptake in mouse brain synaptosomes. Concentrations producing half-maximal enhancement were 2.5 × 10 −8 M (deltamethrin) and 2.2 × 10 −7 M (NRDC 157). This effect was stereospecific: The nontoxic 1 S enantiomers had no significant effect on veratridine-dependent activation. At high deltamethrin concentrations, enhancement was maximal at 5 × 10 −5−1 × 10 −4 M veratridine. Pyrethroid enhancement was completely blocked by 5 × 10 −6 M tetrodotoxin, and neither pyrethroid affected 22Na + uptake in the absence of veratridine at concentrations up to 1 × 10 −5 M. The relative potencies of deltamethrin and NRDC 157 in the synaptosomal sodium channel assay agree well with their relative acute toxicities to mice when administered by intracerebral injection. These findings demonstrate that pyrethroids exemplifying both characteristic poisoning syndromes are potent, stereospecific modifiers of sodium channel function in mammalian brain.