Effect of Dihydrooxadiazines on the Octopamine-Sensitive Adenylate Cyclase Complex of Two-Spotted Spider Mite, Tetranychus urticae Koch

Abstract

The interaction of dihydrooxadiazine insecticides with the octopamine-sensitive adenylate cyclase complex was investigated in homogenates of the two-spotted spider mite, Tetranychus urticae Koch. All tested compounds except a 3-fluoro derivative (compound 8) stimulated cyclic AMP production in mite homogenates. Among the tested dihydrooxadiazines, 4-bromophenyl- (compound 1),2,5-dibromophenyl- (compound 2),3,4-dimethylphenyl- (compound 3), and 4-bromophenyl-2-fluoroethyl- (compound 11) were the most potent in elevating cyclic AMP production although octopamine caused the highest level of cyclic AMP production among all tested chemicals. The selected dihydrooxadiazines (compounds, 1, 2, and 3) showed no additive effects with octopamine. The stimulation of adenylate cyclase in mite homogenates by dihydrooxadiazines was inhibited by several octopaminergic antagonists including mianserin, cyproheptadine, phentolamine, and gramine. The rank-order ability of these antagonists to block adenylate cyclase activation by compounds 1 and 11 was similar to the rank-order ability of the same antagonists to block the enzyme activation by octopamine. The 4-bromophenyl-dihydrooxadiazine (compound 1), octopamine, and 8-Br-cyclic AMP caused an increase in the phosphorylation of proteins that are also phosphorylated by exogenous cyclic AMP-dependent protein kinase. These results support the proposal that the dihydrooxadiazine-induced rise in cyclic AMP levels in mite homogenates results directly in activation of an endogenous cyclic AMP-dependent protein kinase and the primary site of dihydrooxadiazine action is the octopamine-sensitive adenylate cyclase complex.