POSITIVE COUPLING OF BETA-LIKE ADRENERGIC-RECEPTORS WITH ADENYLATE-CYCLASE IN THE CNIDARIAN RENILLA-KOELLIKERI

Coupling of the previously characterized beta1- and beta2-like adrenoc eptors in the sea pansy Renilla koellikeri with adenylate cyclase was examined in membrane preparations from this cnidarian. Adenylate cycla se activity was stimulated by several guanine nucleotides, such as GTP , Gpp(NH)p and GTPgammaS. Fluoride ions and cholera toxin greatly enha nced the enzyme activity, whereas forskolin had no effect on basal or isoproterenol-induced stimulation of the enzyme. The stimulation of ad enylate cyclase activity by several beta-adrenergic agonists in differ ent parts of the animal reflected a positive coupling with the beta2- and beta1-like adrenoceptors in autozooid and peduncle tissues, respec tively. In addition, isoproterenol-induced stimulation of adenylate cy clase activity was dependent on guanine nucleotides, suggesting coupli ng mediated by a G protein. The pharmacological profile of various ant agonists on isoproterenol-sensitive adenylate cyclase in autozooid and peduncle tissues matched that of previous radioligand binding studies . Isoproterenol-induced stimulation of adenylate cyclase activity in r achidial tissues was partially inhibited by trifluoperazine or (+/-)CG P12177 and was completely blocked in the presence of both antagonists. This suggests that coupling of the enzyme occurs with beta1- and beta 2-like adrenoceptors, both being present in the rachis. Serotonin and dopamine were also found to stimulate adenylate cyclase activity. Thei r stimulatory effect was additive to isoproterenol-induced activation, suggesting the presence of dopaminergic and scrotonergic receptors in the tissues of the sea pansy. Along with the data presented previousl y on beta-adrenergic binding, this study suggests that elements of rec eptor-dependent G protein signal transduction originated early in inve rtebrate evolution.