Abstract

Studies were conducted to ascertain whether cells of the IMR-32 human neuroblastoma clone express ligand binding sites and functional responsiveness attributable to ganglia-type nicotinic acetylcholine receptors (nAChR) and/or neuronal/nicotinic alpha-bungarotoxin binding sites. Some comparative studies were conducted using cells of other clonal lines, including BC3H-1 mouse muscle line cells that are known to express muscle-type nAChR. Two classes of specific binding sites for 3H-labeled acetylcholine ([3H]ACh) and a single class of high-affinity, specific 125I-labeled alpha-bungarotoxin binding sites are expressed on membrane fractions prepared from IMR-32 cells. Radioligand binding to these sites on IMR-32 cells is relatively insensitive to blockade by the muscle-type nAChR-selective inhibitors, succinyldicholine and decamethonium, indicating that they are distinct from muscle-type nAChR. [3H]ACh binding to its sites on IMR-32 cell membranes is insensitive to blockade by alpha-bungarotoxin, indicating that IMR-32 cell [3H]ACh and 125I-labeled alpha-bungarotoxin binding sites also can be distinguished. Functional nAChR ion channels of the ganglia-type are expressed by IMR-32 cells, as assessed by the abilities of nicotinic agonists to stimulate 86Rb+ efflux, the relatively higher sensitivity of those responses to blockade by mecamylamine than by d-tubocurarine, and the inability of alpha-bungarotoxin to antagonize nAChR function. These results are consistent with expression by IMR-32 cells of functional ganglia-type nAChR that correlate with high affinity [3H]ACh binding sites as well as expression of a distinct class of neuronal/nicotinic alpha-bungarotoxin binding sites that have a ganglia-type pharmacology.