Functional Coupling of Endogenous Serotonin (5‐HT1B) and Calcitonin (C1a) Receptors in CHO Cells to a Cyclic AMP‐Responsive Luciferase Reporter Gene

: A cyclic AMP‐responsive reporter cell line has been established through the stable expression of a luciferase reporter plasmid in Chinese hamster ovary (CHO) cells. Reporter cells showed a dose‐dependent expression of luciferase in response to incubation with forskolin. These CHO cells were screened for endogenous G protein‐coupled receptors capable of stimulating or inhibiting adenylyl cyclase, by monitoring changes in luciferase expression. Serotonin (5‐HT) receptor agonist ligands caused an inhibition of forskolin‐stimulated luciferase expression in the rank order 5‐carboxamidotryptamine > 5‐HT > sumatriptan > 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin. The response to 5‐HT was reversed by the 5‐HT1 receptor antagonists cyanopindolol and pindolol, but not the 5‐HT2 receptor antagonist ketanserin. Calcitonin was more potent than calcitonin gene‐related peptide (CGRP) at stimulating luciferase expression in this cell line, and these responses were insensitive to the CGRP receptor antagonist, CGRP (8–37). These results were consistent with the presence of 5‐HT1B‐like and calcitonin (C1a‐like) receptors in CHO cells, with the responses to 5‐HT and CGRP being pertussis and cholera toxin‐sensitive, respectively. This reporter gene assay gave the expected pharmacological profile for these receptors when compared with cyclic AMP accumulation assays, confirming its value as a functional assay for G protein‐coupled receptors linked to adenylyl cyclase.