Two different types of inhibitory effects of pyrethroids on nerve Ca- and Ca + Mg-ATPase activity in the squid, Loligo pealei

The biochemical process by which various pyrethroid insecticides affect membrane-bound ATPase activities of the squid nervous system was examined. Of the five ATP-hydrolyzing systems tested, only Ca²⁺-stimulated ATPase activities are seen to be clearly affected by pyrethroids. It was found that the “natural type” pyrethroids (e.g., pyrethrin and allethrin) primarily inhibit Ca-ATPase activity whereas the “highly modified type” pyrethroids (e.g., cypermethrin and decamethrin) mainly inhibit Ca + Mg-ATPase. permethrin, which is considered to possess structural similarities to both the natural type and the highly modified type pyrethroids, was found to have an intermediate property in terms of its inhibitory potency to both Ca- and Ca + Mg-ATPase activities. The level of inhibition of Ca²⁺-stimulated ATPase activities was generally high in the retinal axons and optic lobe synaptosomes but lowest in the axoplasmic preparations.