Octopamine receptors in locust nervous tissue.

The octopamine binding site in the nervous tissue of the migratory locust Locusta migratoria is identified as an octopamine receptor of class 2. The binding of octopamine to the binding site is saturable, reversible, stereospecific and shows a pharmacological profile typical for octopamine receptors. Saturation analysis results in a single class of non-interacting binding sites (KD = 7.9 +/- 0.9 nM; Bmax = 160 fmol/mg). The pharmacological analysis shows that the phenyliminoimidazolidines NC7 and NC5 (Ki = 0.29 and 0.87 nM, respectively) are the most potent agonists, and that mianserin (Ki = 1.20 nM) is the most potent antagonist ever reported for octopamine receptors in direct binding studies.