Stable expression and pharmacological properties of the human α7 nicotinic acetylcholine receptor

The α₇ neuronal nicotinic acetylcholine receptor subtype forms a Ca²⁺-permeable homooligomeric ion channel sensitive to α-bungarotoxin in Xenopus oocytes. In this study, we have stably and functionally expressed the human α₇ cDNA in a mammalian cell line, HEK-293 and examined its pharmacologic properties. [¹²⁵I]α-Bungarotoxin bound to transfected cellswith a K_d value of 0.7 nM and a B_max value of 973 pmol/mg protein. No specific binding was detected in untransfected cells. Specific binding could be displaced by unlabeled α-bungarotoxin (K_i = 0.5 nM and an excellent correlation was observed between binding affinities of a series of nicotinic cholinergic ligands in transfected cells and those in the human neuroblastoma IMR-32 cell line. Additionally, cell surface expression of α₇ receptors was detected by fluorescein isothiocyanate-conjugated α-bungarotoxin in transfected cells. Whole cell currents sensitive to blockade by α-bungarotoxin, and with fast kinetics of activation and inactivation, were recorded from transfected cells upon rapid application of (−)-nicotine or acetylcholine with EC₅₀ values of 49 μM and 155 μM respectively. We conclude that the human α₇ subunit when expressed alone can form functional ion channels and that the stably transfected HEK-293 cell line serves as a unique system for studying human μ₇ nicotinic receptor function and regulation, and for examining ligand interactions.