Characterization of an Adenylate Cyclase-Linked Serotonin (5-HT1) Receptor in a Neuroblastoma × Brain Explant Hybrid Cell Line (NCB-20)

Clonal cell line NCB-20 (a hybrid of mouse neuroblastoma N18TG2 and Chinese hamster 18-day embryonic brain expiant) expressed both high- (K_D 180 nM) and low-affinity (>3000 nM) binding sites for ³H]serotonin (5-HT) which were absent from the parent neuroblastoma. The low-affinity binding site was eliminated by 1 μM spiperone. The order of drug potency for inhibition of high-affinity ³H]5-HT binding was consistent with a 5-HT₁ receptor (5,6 - dihydroxytryptamine = 5-HT = methysergide = 5-methoxytryptamine > cyproheptadine = clozapine = mianserin > spiperone > dopamine = morphine = ketanserin = norepinephrine). ³H]5-HT binding was inhibited by guanine nucleotides (e.g., GTP and Gpp(NH)p), whereas antagonist binding was not; as-corbate was also inhibitory. A 30-min exposure of cells to 1—2 μM 5-HT or other agonists produced a three- to fivefold stimulation of cyclic AMP levels. The order of potency for 5-HT agonist stimulation of basal cyclic AMP levels and 5-HT antagonist reversal of agonist-stimulated levels was the same as the order of drug potency for inhibition of high-affinity ³H]5-HT binding, suggesting linkage of the 5-HT₁ receptor to adenylate cyclase in NCB-20 cells.