Alpha-bungarotoxin sensitive neuronal nicotinic acetylcholine receptors

Current evidence indicates there exists two populations of neuronal nicotinic acetylcholine receptors, the $ alpha$-bungarotoxin ($ alpha$-BGT) sensitive and $ alpha$-BGT insensitive receptors. While the latter are thought to be involved in neurotransmission, the physiological significance of the former are not fully understood. However, evidence suggests that the toxin sensitive receptors may mediate trophic functions. The present studies were carried out to develop and validate novel and unique model systems for studying the structure, function and regulation of the nicotinic $ alpha$-BGT receptor. To this end, two such systems are presented here. First, the immortalized rat hippocampal H19-7 cell line was investigated. This cell line was shown to express a similar set of mRNA encoding for nicotinic receptor subunits as adult rat hippocampus. Further, binding studies using ($ sp{125}$I) -$ alpha$-BGT and other nicotinic ligands demonstrated a similar pharmacological profile between $ alpha$-BGT sites expressed in H19-7 cells and those described in rat brain and primary cultures. The second model system developed involved the stable transfection of the rat $ alpha$7 nicotinic receptor subunit into a rat clonal cell line ($ rm GH sb4C sb1$) which does not endogenously express any nicotinic receptor subunits. RNase protection assays demonstrated that untransfected cells expressed no nicotinic receptor subunit mRNAs, while their transfected counterparts ($ rm alpha7/GH sb4C sb1$ cells) expressed the $ alpha$7 subunit message exclusively. Northern analysis confirmed that the size of the $ alpha$7 message expressed by the transfected cells was similar to the predicted length based on the cDNA used for transfection. The two novel model systems developed and validated in the present studies may serve as an impetus for future studies to delineate the role of the $ alpha$-BGT sensitive neuronal nicotinic acetylcholine receptor