STABLE EXPRESSION AND PHARMACOLOGICAL PROPERTIES OF THE HUMAN ALPHA(7) NICOTINIC ACETYLCHOLINE-RECEPTOR

The alpha(7) neuronal nicotinic acetylcholine receptor subtype forms a Ca2+-permeable homooligomeric ion channel sensitive to alpha-bungarot oxin in Xenopus oocytes. In this study, we have stably and functionall y expressed the human alpha(7) cDNA in a mammalian cell line, HEK-293 and examined its pharmacologic properties. [I-125]alpha-Bungarotoxin b ound to transfected cells with a K-d value of 0.7 nM and a B-max value of 973 pmol/mg protein. No specific binding was detected in untransfe cted cells. Specific binding could be displaced by unlabeled alpha-bun garotoxin (K-i = 0.5 nM) and an excellent correlation was observed bet ween binding affinities of a series of nicotinic cholinergic ligands i n transfected cells and those in the human neuroblastoma IMR-32 cell l ine. Additionally, cell surface expression of alpha(7) receptors was d etected by fluorescein isothiocyanate-conjugated alpha-bungarotoxin in transfected cells. Whole cell currents sensitive to blockade by a-bun garotoxin, and with fast kinetics of activation and inactivation, were recorded from transfected cells upon rapid application of (-)-nicotin e or acetylcholine with EC(50) values of 49 mu M and 155 mu M respecti vely. We conclude that the human alpha(7) 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 alpha(7) ni cotinic receptor function and regulation, and for examining ligand int eractions.