Frequency-dependent effects of the pyrethroid insecticide decamethrin in frog myelinated nerve fibres.

The pyrethroid insecticide decamethrin (10(-6) M) caused a frequency-dependent depression of the action potential in frog myelinated nerve fibres which was associated with a progressive membrane depolarisation brought about by summation of depolarising after-potentials. Voltage clamp experiments with single nodes of Ranvier showed that this afterpotential was most probably due to a long-lasting prolongation of the transient increase in sodium permeability of the membrane. The results indicate that decamethrin, like the other pyrethroids, specifically affects the sodium channels of the nerve membrane.