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

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Abstract
Clonal cell line NCB-20 (a hybrid of mouse neuroblastoma N18TG2 and Chinese hamster 18-day embryonic brain explant) expressed both high- (KD 180 nM) and low-affinity (> 3000 nM) binding sites for [3H]serotonin (5-HT) [5-hydroxytryptamine] which were absent from the parent neuroblastoma. The low-affinity binding sites were eliminated by 1 .mu.M 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 = methylsergide = 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 [guanyl-5''-yl-imidodiphosphate]), whereas antagonist binding was not; ascorbate was also inhibitory. A 30-min exposure of cells to 1-2 .mu.M 5-HT or other agonists produced a 3- to 5-fold stimulation of cAMP levels. The order of potency for 5-HT agonist stimulation of basal cAMP 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.