Interaction of pyrethroids with the ion transport pathways present in frog skin

We measured the ability of deltamethrin and permethrin to stimulate the ion transport operated by the frog skin. Ion transport was monitored by measuring the short-circuit current. Deltamethrin and permethrin, added to the fluid bathing the internal surface of the isolated frog skin, showed a seasonal feature and were more effective in increasing short-circuit current in the period between June and October. Transepithelial influxes and outfluxes of Na-22(+) and Cl-36(-) across symmetrical parts of the short-circuited skin were then measured. Deltamethrin was found to increase net Naf absorption and, to a lesser extent, Cl- secretion. The presence of a Cl- secretory mechanism is supported by two observations, those being that the short-circuit current value, recorded when deltamethrin and amiloride (inhibitor of NaC channels) were simultaneously present, was higher than that obtained in the presence of amiloride alone and that bumetanide, a classic inhibitor of Cl- secretion, completely inhibited the component of the Cl- outflux that was induced by the deltamethrin stimulation. The stimulations of short-circuit current respectively caused by deltamethrin (type II pyrethroid) and permethrin (type I) were comparable and similarly affected by indomethacin (an inhibitor of cyclooxygenase) and W7 (an inhibitor of the Ca2+/calmodulin system). These findings suggest that, in frog skin, the cellular mechanism of action of type I and type II pyrethroids is similar.