Pharmacological Characterization of Cholinergic Receptors in a Human Neuroblastoma Cell Line

A human neuroblastoma cell line, IMR32, has been characterized as far as morphology, membrane receptors for neurotransmitters, and uptake and release of 3H]3,4-dihydroxyphenylethylamine (3H]dopamine). These cells expressed at their surface both nicotinic and muscarinic cholinergic receptors, revealed by 125I]alpha-bungarotoxin and 3H]quinuclidinylbenzilate (3H]QNB) binding, respectively. 125I]alpha-Bungarotoxin binding was efficiently inhibited by alpha-bungarotoxin, nicotine, carbachol, and d-tubocurarine. 3H]QNB binding was competitively inhibited by atropine, pirenzepine, and carbachol. Hexamethonium did not affect the binding of either ligand. In competition experiments with 3H]QNB, pirenzepine recognized only one binding site with "low affinity," and carbachol recognized two sites with different affinities. beta-adrenergic receptors were present in a very low amount, whereas alpha-adrenergic and dopaminergic receptors were not detectable. IMR32 cells had an imipramine-sensitive 3H]dopamine uptake, but carbachol, high levels of K+, the calcium ionophore A23187, and alpha-latrotoxin were not able to induce release of 3H]dopamine that had been taken up. The ultrastructural analysis showed that IMR32 cells contained very few dense-core vesicles, suggesting a low storage capacity for neurotransmitter. These cells could be an useful in vitro model for studying neurotransmitter receptors of the human CNS.