Abstract

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 α-bungarotoxin (αBgt), nearly all of which contain only α7 subunits (α7-nAChRs) and those insensitive to αBgt, which contain α3, α5, β4, and, in some cases, β2 subunits (α3*-nAChRs). We explored the relationship between nAChR composition and channel function using toxins recognizing α7 subunits (αBgt), and α3/β4 (α-conotoxin-AuIB), or α3/β2 (α-conotoxin-MII) subunit interfaces to perturb responses induced by nicotine, α7-, or α3-selective agonists (GTS-21 or epibatidine, respectively). Using these reagents, fast-decaying whole-cell current components were attributed solely to α7-nAChRs, and slow-decaying components mostly to α3*-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 α7-nAChRs, and long 25- and 40-pS events to α3*-nAChRs. α3*-nAChRs lacking β2 subunits seemed responsible for long 25 pS nAChR events, whereas those containing β2 subunits mediated the long 40 pS nAChR events that dominate single-channel records. These results reveal greater functional heterogeneity for α7-nAChRs than previously expected and indicate that β2 subunits contribute importantly to α3*-nAChR function. By linking structural to functional nAChR subtypes, the findings also illustrate a useful pharmacological strategy for selectively targeting nAChRs.