The Sf9 cell line as a model for studying insect octopamine-receptors

Abstract

Adenylate cyclase-coupled octopamine (OA) receptors were demonstrated in the Sf9 insect cell line derived from Spodoptera frugiperda. This receptor-enzyme complex is membrane-associated, has a requirement for GTP and is forskolin-sensitive. In intact Sf9 cells, 100 μM OA produces a 3-fold increase in cyclic AMP (cAMP) levels. These cells do not exhibit adenylate cyclase sensitive to dopamine or serotonin. This binding site shows a high affinity for OA ( K a = 3.5 μM), the formamidine, N-demethylchlordimeform, DCDM ( K a = 0.3 μM) and the imidazoline, 2,3-xylylaminomethyl-2′-imidazoline, XAMI ( K a = 0.7 μM) with a reduced affinity for α 2-selective agonists such as clonidine and UK-14304. Of 24 putative antagonists tested in this system, ergotamine, phentolamine, (+)mianserin and RX821002A were the most effective. Other antagonists such as yohimbine, propranolol and (+)butaclamol were relatively ineffective. These responses differ considerably from the pharmacological profile for the cockroach nerve cord octopamine-sensitive adenylate cyclase (OSAC) but are similar to previous results with the lepidopteran, Manduca sexta. There appears to be a closer pharmacological relationship of the Sf9 and cockroach OA receptor to the vertebrate imidazoline-preferring receptor (IPR) than the α 2-adrenergic receptor. Studies on receptor dynamics indicated that the Sf9 OSAC undergoes agonist-induced desensitization. Therefore, based on these combined data, we propose the Sf9 cell line as a convenient model system for studying the pharmacology and dynamics of lepidopteran adenylate cyclase-coupled OA receptors.