Identification of neuron-specific ivermectin binding sites in Drosophila melanogaster and Schistocerca americana.

High affinity avermectin binding sites have been identified and partially characterized in membranes from two insect species, Drosophila melanogaster and the locus Schistocerca americana. There is a 10-fold increase in the density of ivermectin binding sites associated with membranes isolated from Drosophila heads (a neuronally enriched tissue source) compared to the bodies (Bmax values were 3.5 and 0.22 pmol/mg, respectively) with only a small difference in the apparent dissociation constant (Kd values of 0.20 and 0.34 nM for heads and bodies, respectively). Membranes prepared from metathoracic ganglia of the locust, Schistocerca americana, were highly enriched in high affinity avermectin binding sites (Kd = 0.2 nM and Bmax = 42 pmol/mg). Using an [125I]arylazido-avermectin analog as a photoaffinity probe, a 45 kDa protein was identified in both the Drosophila head and body tissue preparations. A 45 kDa protein was also specifically labeled with [125I]azido-avermectin in the locust neuronal membranes.