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

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 ␣-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.

T Cells Express α7-Nicotinic Acetylcholine Receptor Subunits That Require a Functional TCR and Leukocyte-Specific Protein Tyrosine Kinase for Nicotine-Induced Ca2+ Response

“…The observation that the -chain-deficient TCR/ CD3 complex is ineffective in transmitting signals to raise [Ca 2ϩ ] i in response to nicotine further supports this inference. ␣-BTX and MLA are considered relatively specific antagonists of ␣7-nAChRs and block nicotine-induced currents in neuronal cells (16). However, contrary to their action in PC12 cells, both ␣-BTX and MLA stimulated a strong Ca 2ϩ response in T cells.…”

“…In mammals, these receptors are also widely expressed in nonexcitable cells such as keratinocytes (12), lung type-2 epithelial cells (13,14), and macrophages (15), but their structure and function on non-neuronal cells are not clearly defined. Although in neurons, the ␣7-nAChRs participate in neurotransmission which is blocked by ␣-bungarotoxin (␣-BTX) and methyllycaconitine (MLA) (16,17), it is unlikely that these receptors perform such a function in nonexcitable cells. Chronic in vivo nicotine treatment suppresses the immune and inflammatory responses (18 -20), causing T cell anergy (21) and decreased leukocyte migration; however, acute exposure to nicotine increases intracellular calcium [Ca 2ϩ ] i and cell migration in several cell types (18,14,22,23).…”

Neonatal intermittent hypoxia impairs neuronal nicotinic receptor expression and function in adrenal chromaffin cells

“…2, A and B). Further analysis with selective blockers of nAChR subunits revealed that ␣-conotoxin AulB (10 M; conotoxin), an inhibitor of ␣ 3 containing nAChRs, (14,22), reduced the nicotine-evoked increase in [Ca 2ϩ ] i by ϳ60% (P Ͻ 0.001), whereas methyllcaconitine (50 nM), a selective inhibitor of ␣ 7 -nAChRs (30), caused a modest (24%) but significant attenuation of the [Ca 2ϩ ] i response to nicotine (P Ͻ 0.05; Fig. 2, A and B).…”

Activation of Nicotinic Acetylcholine Receptors Decreases Apoptosis in Human and Female Murine Pancreatic Islets

“…icotinic acetylcholine receptors (nACh-Rs) belong to a family of ligand-gated channels that form a cationselective pathway across the plasma membrane of a given cell (1) and consist of hetero-or homopentamers of 17 different ␣-, ␤-, ␥-, ␦-, and ⑀-subunits that determine the properties of the channel (2,3). They are implicated in neuronal processes such as synaptic transmission but also in the regulation of neuronal cell death in response to injuries such as hypoxia and glutamate excitotoxicity (4) and, outside the central nervous system, in the modulation of peripheral inflammation (5,6).…”