High-affinity octopamine receptors revealed in Drosophila by binding or [3H]octopamine

The study describes, for the first time, detection of a putative, high-affinity octopamine receptor by direct binding studies with a radiolabeled ligand. Crude membranes prepared from heads of Drosophila melanogaster bind [3H]octopamine at a level of 0.4 pmol per mg protein with an apparent Kd of 5 nM. Low concentrations of dihydroergotamine, phentolamine and chloropromazine, but not of propranolol and serotonergic ligands, were potent displacers of [3H]octopamine binding. The [3H]octopamine binding assay may prove useful in assessing the potency of novel octopaminergic ligands.