Effect of insecticides on the short-circuit current and resistance of isolated frog skin

The effects of aldrin, carbaryl, α- and γ-chlordane, dichlorodiphenyldichloroethane (DDD), dichlorodiphenyltrichloroethane (DDT), dieldrin, endrin, heptachlor, lindane, methoxychlor, and nonachlor on the short-circuit current and resistance of the isolated intact frog skin were studied. The short-circuit current is approximately equivalent to the rate of active transport of sodium, while the resistance indicates the summed ionic permeability of the skin. At a concentration of 2 × 10^?4M, only carbaryl, DDD, dieldrin, and lindane produced significant (P<0.05, paired t test) changes in the short-circuit current. Nonachlor produced a decrease (P=0.12) in the short-circuit current and also increased the resistance (P=0.07). DDD, dieldrin, and carbaryl caused significant increases in short-circuit current while at the same time the resistance was significantly decreased. Lindane increased both the short-circuit current and the resistance. It was concluded that the frog skin probably contains effective permeability barriers that prevent externally applied insecticides from reaching the site of active sodium transport. It appeared likely that most of the insecticides produced the observed effects on the frog skin by altering the sodium permeability of the outer barrier.