Species differences in chlorantraniliprole and flubendiamide insecticide binding sites in the ryanodine receptor

Anthranilic and phthalic diamides exemplified by chlorantraniliprole (Chlo) or cyantraniliprole (Cyan) and flubendiamide (Flu), respectively, are the newest major chemotype of insecticides with outstanding potency, little or no cross resistance with other classes and low mammalian toxicity. They are activators of the ryanodine (Ry) receptor (RyR)-Ca²⁺ channel, based on Ca²⁺ flux and electrophysiology investigations. The goal of this study is to define species differences in the degree and mechanisms of diamide selective action by radioligand specific binding studies at the ³H]Ry, ³H]Chlo and ³H]Flu sites. The ³H]Ry site is observed in muscle of lobster, rabbit and four insect species (Musca domestica, Apis mellifera, Heliothis virescens and Agrotis ipsilon) whereas the ³H]Chlo site is evident in the four insects and the ³H]Flu site in only the two lepidoptera (Agrotis and Heliothis). ³H]Ry binding is significantly stimulated by Chlo, Cyan and Flu with the insects (except Flu with Musca) but not the lobster and rabbit. ³H]Chlo binding is stimulated by Ry and Flu in Musca and Apis but not in the lepidoptera, while Flu and Cyan are inhibitory. ³H]Flu binding is strongly inhibited by Chlo and Cyan in Agrotis and Heliothis. ³H]Chlo and ³H]Flu binding are not dependent on added Ca²⁺ or ATP in Heliothis and Agrotis whereas the other radioligand-receptor combinations are usually enhanced by Ca²⁺ and ATP. More generally, there are species differences in the Ry, Chlo and Flu binding sites of the RyR that may confer selective toxicity and determine target site cross resistance mechanisms.