Pharmacological characterization of octopamine-sensitive adenylate cyclase in the flight muscle of Locusta migratoria L.

Octopamine stimulates (20-30-fold) the adenylate cyclase activity in a broken cell preparation of locust flight muscle. This stimulation is mediated by one receptor with an apparent affinity of 3.3 X 10(-6) M. The hydroxyl group in the para position on phenylethanolamine was absolutely necessary to obtain an agonist whereas the meta hydroxyl group or the presence of a catechol almost suppressed the activity. Similar pharmacological profiles were obtained on other locust muscles, i.e. mandibular and extensor tibiae muscles. The affinities of a large series of agonists and antagonists for the octopamine receptor coupled with an adenylate cyclase were compared to those reported for octopamine 1, 2A and 2B receptors based on physiological studies in the locust extensor tibiae muscle. It appears that the octopamine receptor coupled with adenylate cyclase is likely to be identical with the octopamine 2A receptor mediating the increase in the amplitude of slow motoneuron twitch tension. The results of the pharmacological experiments are discussed, in particular concerning the possible relationship between the octopamine receptor and alpha 1- and alpha 2-adrenoceptors.