Inducible, heterologous expression of human α7-nicotinic acetylcholine receptors in a native nicotinic receptor-null human clonal line

Tetracycline-regulated expression of recombinant nicotinic acetylcholine receptors (nAChR) composed of human α7 subunits is achieved in native nAChR- null SH-EP1 human epithelial cells. α7 subunits are heterologously expressed as messenger RNA and as components of ¹²⁵I-labeled α-bungarotoxin (I- Bgt)-binding nAChR (~ 10 pmol per milligram of membrane protein) at levels sensitive to the amount of tetracycline in cell growth medium. I-Bgt-binding α7-nAChR appear on the cell surface pool and in intracellular pools. The pharmacological profile for drug competition toward I-Bgt binding to these recombinant α7-nAChR matches that of human native α7-nAChR naturally expressed in SH-SY5Y human neuroblastoma cells (rank order potency methyllycaconitine > 1,1-dimethyl-4-phenylpiperazinium > (-)nicotine > cytisine > carbamylcholine ≥ D-tubocurarine). Chronic exposure to nicotine induces up-regulation of human recombinant α7-nAChR (80% up-regulation at 10 μM nicotine) just as it does native α7-nAChR in other human cell lines. These studies confirm expression of nAChR as homooligomers of human α7 subunits from transgenes, establish a native nAChR-null background for such expression, and demonstrate that this expression can be regulated to facilitate studies of human α7-nAChR.