Interaction of pyrethroids with 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 measur ing the short-circuit current. Deltamethrin and permethrin, added to the fl uid bathing the internal surface of the isolated frog skin, showed a season al feature and were more effective in increasing short-circuit current in t he period between June and October. Transepithelial influxes and outfluxes of Na-22(+) and Cl-36(-) across symmetrical parts of the short-circuited sk in were then measured. Deltamethrin was found to increase net Naf absorptio n and, to a lesser extent, Cl- secretion. The presence of a Cl- secretory m echanism is supported by two observations, those being that the short-circu it current value, recorded when deltamethrin and amiloride (inhibitor of Na C channels) were simultaneously present, was higher than that obtained in t he presence of amiloride alone and that bumetanide, a classic inhibitor of Cl- secretion, completely inhibited the component of the Cl- outflux that w as induced by the deltamethrin stimulation. The stimulations of short-circu it current respectively caused by deltamethrin (type II pyrethroid) and per methrin (type I) were comparable and similarly affected by indomethacin (an inhibitor of cyclooxygenase) and W7 (an inhibitor of the Ca2+/calmodulin s ystem). These findings suggest that, in frog skin, the cellular mechanism o f action of type I and type II pyrethroids is similar.