NATIVE NICOTINIC ACETYLCHOLINE-RECEPTORS IN HUMAN IMR32 NEUROBLASTOMA-CELLS - FUNCTIONAL, IMMUNOLOGICAL AND PHARMACOLOGICAL PROPERTIES

IMR32 cells express two classes of surface nicotinic receptors: those labelled with high affinity by [I-125]neuronal toxin, and those labell ed by [(125)]alpha-bungarotoxin. Whole-cell patch-clamp recordings ind icate that both classes of receptor are able to elicit inward currents that are totally blocked by d-tubocurarine but only partially blocked by alpha-bungarotoxin. In IMR32 cells, nicotine induces an increase i n the intracellular level of free Ca2+. This increase, which is also c ompletely blocked by d-tubocurarine and only partially blocked by alph a-bungarotoxin and Cd2+, is due to extracellular calcium influx throug h both the nicotinic receptors and the voltage-activated Ca2+ channels . By using subunit-specific polyclonal antibodies, we have demonstrate d that the alpha-bungarotoxin receptors contain the alpha 7 subunit, b ut none of the other subunits whose transcripts are present in IMR32 c ells. The pharmacological profile of these human alpha 7-containing al pha-bungarotoxin receptors is similar to that observed in the native c hick alpha 7 receptor, but there are also some species-specific differ ences.