Characterization Of Human Î±4Î²2-Nicotinic Acetylcholine Receptors Stably And Heterologously Expressed In Native Nicotinic Receptor-Null Sh-Ep1 Human Epithelial Cells
Naturally expressed nicotinic acetylcholine receptors composed of Î±4 and Î²2 subunits (Î±4Î²2-nAChR) are the predominant form of high affinity nicotine binding site in the brain implicated in nicotine reward, mediation of nicotinic cholinergic transmission, modulation of signaling through other chemical messages, and a number of neuropsychiatric disorders. To develop a model system for studies of human Î±4Î²2-nAChR allowing protein chemical, functional, pharmacological, and regulation of expression studies, human Î±4 and Î²2 subunits were stably introduced into the native nAChR-null human epithelial cell line SH-EP1. Heterologously expressed Î±4Î²2-nAChR engage in high-affinity, specific binding of 3H-labeled epibatidine (H-EBDN; macroscopic KD = 10 pM; kon = 0.74/min/nM, koff = 0.013/min). Immunofluorescence studies show Î±4 and Î²2 subunit protein expression in virtually every transfected cell, and microautoradiographic studies show expression of 125I-labeled jodo-deschloroepibatidine binding sites in most cells. H-EBDN binding competition studies reveal high affinity for nicotinic agonists and lower affinity for nicotinic antagonists. Heterologously expressed Î±4Î²2-nAChR functional studies using 86Rb+ efflux assays indicate full efficacy of epibatidine, nicotine, and acetylcholine; partial efficacy for 1,1-dimethyl-4-phenyl-piperazinium, cytisine, and suberyldicholine; competitive antagonism by dihydro-Î² -erythroidine, decamethonium, and methyllycaconitine; noncompetitive antagonism by mecamylamine and eserine; and mixed antagonism by pancuronium, hexamethonium, and d-tubocurarine. These results demonstrate utility of transfected SH-EP1 cells as models for studies of human Î±4Î²2-nAChR, and they also reveal complex relationships between apparent affinities of drugs for radioligand binding and functional sites on human Î±4Î²2-nAChR.
Digital Object Identifier (DOI)
Eaton, J. Brek; Peng, Jian Hong; Schroeder, Katherine M.; George, Andrew A.; Fryer, John D.; Krishnan, Chandra; Buhlman, Lori; Kuo, Yen Ping; Steinlein, Ortrud; and Lukas, Ronald J., "Characterization Of Human Î±4Î²2-Nicotinic Acetylcholine Receptors Stably And Heterologously Expressed In Native Nicotinic Receptor-Null Sh-Ep1 Human Epithelial Cells" (2003). Neurobiology. 71.