Abstract
The differential action of the novel agonist JN403 at neuronal α7 and muscle nicotinic receptors (AChRs) was explored by using a combination of functional and structural approaches. Single-channel recordings reveal that JN403 is a potent agonist of α7 but a very low-efficacy agonist of muscle AChRs. JN403 elicits detectable openings of α7 and muscle AChRs at concentrations ~1000-fold lower and ~20-fold higher, respectively, than that for ACh. Single-channel activity elicited by JN403 is very similar to that elicited by ACh in α7 but profoundly different in muscle AChRs, where openings are brief and infrequent and do not appear in clusters at any concentration. JN403 elicits single-channel activity of muscle AChRs lacking the ε subunit, with opening events being more frequent and prolonged than those of wild-type AChRs. This finding is in line with the molecular docking studies predicting that JN403 may form a hydrogen bond required for potent activation at the α-δ but not at the α-ε binding site. JN403 does not elicit detectable Ca²⁺ influx in muscle AChRs but inhibits (±)-epibatidine-elicited influx mainly by a noncompetitive mechanism. Such inhibition is compatible with single-channel recordings revealing that JN403 produces open-channel blockade and early termination of ACh-elicited clusters, and it is therefore also a potent desensitizing enhancer of muscle AChRs. The latter mechanism is supported by the JN403-induced increase in the level of binding of [³H]cytisine and [³H]TCP to resting AChRs. Elucidation of the differences in activity of JN403 between neuronal α7 and muscle AChRs provides further insights into mechanisms underlying selectivity for α7 AChRs.
Publication types
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Comparative Study
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Calcium Signaling / drug effects
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Carbamates / metabolism
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Carbamates / pharmacology*
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Cell Line
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Fetal Proteins / agonists
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Fetal Proteins / chemistry
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Fetal Proteins / genetics
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Fetal Proteins / metabolism
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Humans
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Kinetics
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Membrane Potentials / drug effects
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Mice
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Molecular Conformation
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Molecular Docking Simulation
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Muscle Proteins / agonists*
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Muscle Proteins / chemistry
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Muscle Proteins / genetics
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Muscle Proteins / metabolism
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Nerve Tissue Proteins / agonists*
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Nerve Tissue Proteins / chemistry
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / metabolism
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Nicotinic Agonists / metabolism
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Nicotinic Agonists / pharmacology*
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Nicotinic Antagonists / chemistry
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Nicotinic Antagonists / metabolism
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Nicotinic Antagonists / pharmacology
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Protein Binding
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Protein Subunits / agonists
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Protein Subunits / chemistry
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Protein Subunits / genetics
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Protein Subunits / metabolism
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Quinuclidines / metabolism
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Quinuclidines / pharmacology*
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Receptors, Nicotinic / chemistry
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Receptors, Nicotinic / genetics
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Receptors, Nicotinic / metabolism*
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Recombinant Proteins / chemistry
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Recombinant Proteins / metabolism
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Torpedo
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alpha7 Nicotinic Acetylcholine Receptor / agonists*
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alpha7 Nicotinic Acetylcholine Receptor / chemistry
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alpha7 Nicotinic Acetylcholine Receptor / genetics
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alpha7 Nicotinic Acetylcholine Receptor / metabolism
Substances
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(S)-(1-azabicyclo(2.2.2)oct-3-yl)carbamic acid (S)-1-(2-fluorophenyl) ethyl ester
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CHRNA1 protein, human
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Carbamates
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Chrna7 protein, human
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Fetal Proteins
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Muscle Proteins
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Nerve Tissue Proteins
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Nicotinic Agonists
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Nicotinic Antagonists
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Protein Subunits
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Quinuclidines
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Receptors, Nicotinic
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Recombinant Proteins
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alpha7 Nicotinic Acetylcholine Receptor