Characterisation of an octopamine-sensitive adenylate cyclase in haemocyte membrane fragments of the American cockroach Periplaneta americana L.

Abstract An octopamine-sensitive adenylate cyclase has been studied in a fragmented haemocyte-membrane preparation of the American cockroach, Periplaneta americana . The enzyme complex is similar to that of adenylate cyclases from other eukaryotic cells in having a requirement for magnesium ions and GTP and in displaying elevated prodution of cyclic AMP in the presence of sodium fluoride and forskolin. The preparation responds to GTP in a dose-dependent manner and a positive dose-dependent response to calmodulin is also reported. Octopamine and synephrine are the most potent stimulators of cyclic AMP production in the haemocyte-membrane preparation and additivity studies indicate that synephrine and another activator, tyramine, are interacting with the enzyme complex through the octopamine-receptor. The adrenergic agonists, naphazoline and clonidine increased cyclic AMP production and the formamidines, demethylchlordimeform and BTS 27271 also were effective in this regard. Hydroxymandelic acid caused a slight but statistically significant decrease in cyclic AMP production. The most potent antagonists of the octopamine-mediated response were mianserin > promethazine > phentolamine > gramine > cis- flupenthixol > dibenamine. Lineweaver-Burk plots indicate that the mianserin, promethazine and gramine-effects, as with earlier reports for phentolamine, result from competitive inhibition