Roles For Nicotinic Acetylcholine Receptor Subunit Large Cytoplasmic Loop Sequences In Receptor Expression And Function
To evaluate possible physiological roles of the large cytoplasmic loops (C2) and neighboring transmembrane domains of nicotinic acetylcholine receptor (nAChR) subunits, we generated novel fusion constructs in which human nAChR Î±4, Î²2, or Î²4 subunit C2 or C2 and neighboring sequences were replaced by corresponding sequences from the mouse serotonin type 3A (5-HT 3A) receptor subunit. Following stable expression in human SH-EP1 cells, we found that extensive sequence substitutions involving third and fourth transmembrane domains and neighboring \"proximal\" C2 sequences (e.g., Î²2 H322-V335 and V449-R460) did not allow functional expression of nAChR containing chimeric subunits. However, expression of functional nAChR was achieved containing wild-type Î±4 subunits and chimeric Î²2 (Î²2Ï‡) subunits whose \"nested\" C2 domain sequences K336-S448 were replaced with the corresponding 5-HT3A subunit sequences. Whereas these findings suggested indispensable roles for M3/M4 transmembrane and/or proximal C2 sequences in Î±4Î²2-nAChR function, nested C2 sequences in the Î²2 subunit are not essential for functional receptor expression. Ligand-binding analyses also revealed only subtle differences in pharmacological profiles of Î±4Î²2-nAChR compared with Î±4Î²2Ï‡-nAChR. Nevertheless, there was heightened emergence of agonist-mediated self-inhibition of Î±4Î²2Ï‡ function, greater sensitivity to functional blockade by a number of antagonists, and faster and more complete acute desensitization of Î±4Î²2Ï‡-nAChR than for Î±4Î²2-nAChR. These studies are consistent with unexpected roles of nested C2 sequences in nAChR function. Copyright Â© 2005 by The American Society for Pharmacology and Experimental Therapeutics.
Journal of Pharmacology and Experimental Therapeutics
Digital Object Identifier (DOI)
Kuo, Yen Ping; Xu, Lin; Eaton, J. Brek; Zhao, Lingke; Wu, Jie; and Lukas, Ronald J., "Roles For Nicotinic Acetylcholine Receptor Subunit Large Cytoplasmic Loop Sequences In Receptor Expression And Function" (2005). Neurobiology. 272.