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Weiss S, Drummond GI. 
“Dopamine- And Serotonin-sensitive Adenylate Cyclase In The Gill Of Aplysia”. 
Federation Proceedings. 1981;40(3, Pt 1):316.
Stimulation of adenylate cyclase by dopamine (M) and serotonin (5-HT) was examined in 38,000 x 9 pellets from Aphasia gill homogenates. DA stimulated enzyme activity 3 to 5-fold over basal (EC50, 10 mcM), 5-HT stimulated 15 to 20-fold (EC50, 1mcM). Several ergot alkaloids were also effective. LSD-25 acted as a partial agonist (efficacy 0.45, EC50,2mcM),ergotamine was equieffective to 5-HT but 10 times more potent (EC50, 0.1mcM). At subsaturating concentrations of 5-HT (10 nM to l mcM), DA (5 mcM) further augmented enzyme activity; at saturating concentrations of 5-HT (10-100 mcM), DA produced no additional stimulation. Activation by structural analogs of DA and 5-HT provided evidence for similar structural requirements for both agonists. Stimulation by DA, 5-HT and ergotamine was antagonized by the 5-HT antagonists 2-bromo-LSD, methergoline, and cyproheptadine and also by the DA antagonists chlorpromazine and haloperidol. Stimulation by ergotamine in the presence of 50 mcM chlorpromazine or methergoline resulted in a rightward-shifted two component dose-response curve. The first component (EC50, 0.5 mcM) accounted for 750f total stimulation by ergotamine,the second component (EC50, 25mcM) accounted for the remainder. These findings suggest that structural similarities exist between the receptors that mediate DA and 5-HT stimulation of adenylate cyclase. Saturating concentrations of 5-HT or ergotamine may fully activate both M and 5-HT receptors resulting in maximum activation of the enzyme.
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