Vol. 63, Issue 2, 311-324, February 2003

Relating Neuronal Nicotinic Acetylcholine Receptor Subtypes Defined by Subunit Composition and Channel Function

Qiang Nai, J. Michael McIntosh, and Joseph F. Margiotta

Department of Anatomy and Neurobiology, Medical College of Ohio, Toledo, Ohio (Q.N., J.F.M.); and Department of Biology, University of Utah, Salt Lake City, Utah (J.M.M.)

Neuronal nicotinic acetylcholine receptors (nAChRs) are widespread, diverse ion channels involved in synaptic signaling, addiction, and disease. Despite their importance, the relationship between native nAChR subunit composition and function remains poorly defined. Chick ciliary ganglion neurons express two major nAChR types: those recognized by -bungarotoxin (Bgt), nearly all of which contain only 7 subunits (7-nAChRs) and those insensitive to Bgt, which contain 3, 5, 4, and, in some cases, 2 subunits (3*-nAChRs). We explored the relationship between nAChR composition and channel function using toxins recognizing 7 subunits (Bgt), and 3/4 (-conotoxin-AuIB), or 3/2 (-conotoxin-MII) subunit interfaces to perturb responses induced by nicotine, 7-, or 3-selective agonists (GTS-21 or epibatidine, respectively). Using these reagents, fast-decaying whole-cell current components were attributed solely to 7-nAChRs, and slow-decaying components mostly to 3*-nAChRs. In outside-out patches, nicotine activated brief 60- and 80-pS single nAChR channel events, and mixed-duration 25- and 40-pS nAChR events. Subsequently, 60- and 80-pS nAChR events and most brief 25- and 40-pS events were attributed to 7-nAChRs, and long 25- and 40-pS events to 3*-nAChRs. 3*-nAChRs lacking 2 subunits seemed responsible for long 25 pS nAChR events, whereas those containing 2 subunits mediated the long 40 pS nAChR events that dominate single-channel records. These results reveal greater functional heterogeneity for 7-nAChRs than previously expected and indicate that 2 subunits contribute importantly to 3*-nAChR function. By linking structural to functional nAChR subtypes, the findings also illustrate a useful pharmacological strategy for selectively targeting nAChRs.