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Nicotine stimulates ion transport via metabotropic ?4 subunit containing nicotinic ACh receptors.

ABSTRACT: Background and purpose: Mucociliary clearance is an innate immune process of the airways, essential for removal of respiratory pathogens. It depends on ciliary beat and ion and fluid homeostasis of the epithelium. We have shown that nicotinic ACh receptors (nAChRs) activate ion transport in mouse tracheal epithelium. Yet the receptor subtypes and signalling pathways involved remained unknown.

Experimental approach: Transepithelial short circuit currents (I_SC ) of freshly isolated mouse tracheae were recorded using the Ussing chamber technique. Changes in [Ca²⁺ ]_i were studied on freshly dissociated mouse tracheal epithelial cells.

Key results: Apical application of the nAChR agonist nicotine transiently increased I_SC . The nicotine effect was abolished by the nAChR antagonist mecamylamine. ?-Bungarotoxin (?7 antagonist) had no effect. The agonists epibatidine (?3?2, ?4?2, ?4?4 and ?3?4) and A-85380 (?4?2 and ?3?4) increased I_SC . The antagonists dihydro-?-erythroidine (?4?2, ?3?2, ?4?4 and ?3?4), ?-conotoxin MII (?3?2) and ?-conotoxin PnIA (?3?2) reduced the nicotine effect. Nicotine- and epibatidine-induced currents were unaltered in ?2^-/- mice, but in ?4^-/- mice no increase was observed. In the presence of thapsigargin (endoplasmatic reticulum Ca²⁺ -ATPase inhibitor) or the ryanodine receptor antagonists JTV-519 and dantrolene there was a reduction in the nicotine-effect, indicating involvement of Ca²⁺ release from intracellular stores. Additionally, the PKA inhibitor H-89 and the TMEM16A (Ca²⁺ -activated chloride channel) inhibitor T16Ainh-A01 significantly reduced the nicotine-effect.

Conclusion and implications: ?3?4 nAChRs are responsible for the nicotine-induced current changes via Ca²⁺ release from intracellular stores, PKA and ryanodine receptor activation. These nAChRs might be possible targets to stimulate chloride transport via TMEM16A.

SUBMITTER: Kumar P

PROVIDER: S-EPMC7707097 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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Nicotine stimulates ion transport via metabotropic β4 subunit containing nicotinic ACh receptors.

Kumar Praveen P Scholze Petra P Fronius Martin M Krasteva-Christ Gabriela G Hollenhorst Monika I MI

British journal of pharmacology 20201109 24

<h4>Background and purpose</h4>Mucociliary clearance is an innate immune process of the airways, essential for removal of respiratory pathogens. It depends on ciliary beat and ion and fluid homeostasis of the epithelium. We have shown that nicotinic ACh receptors (nAChRs) activate ion transport in mouse tracheal epithelium. Yet the receptor subtypes and signalling pathways involved remained unknown.<h4>Experimental approach</h4>Transepithelial short circuit currents (I<sub>SC</sub> ) of freshly ...[more]

PMID: 32959891

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Project description:Nicotine leads to both activation and desensitization (inactivation) of nicotinic acetylcholine receptors (nAChRs). This study tested the hypothesis that nicotine and a selective antagonist of ?2*nAChRs would have similar effects on affective behavior. Adult C57BL/6J male mice were tested in a conditioned emotional response (CER) assay which evaluates the ability of an aversive stimulus to inhibit goal-directed behavior. Mice lever-pressed for a saccharin reinforcer according to a variable schedule of reinforcement during sessions in which two presentations of a compound light/tone conditioned stimulus (CS) co-terminated with a 0.1 or 0.3 mA, 0.5 s footshock unconditioned stimulus (US). During testing in the absence of the US, mice received doses of i.p. nicotine (0, 0.0032, 0.01, 0.032, 0.1 mg/kg) or a selective ?2 subunit containing nAChR (?2*nAChR) antagonist dihydro-beta-erythroidine (0, 0.1, 0.3, 1.0, 3.0 mg/kg DH?E). There was a dose-dependent effect of nicotine revealing that only low doses (0.01, 0.032 mg/kg) increased CER suppression ratios (SR) in these mice. DH?E also dose-dependently increased SR at the 3 mg/kg dose. In ethological measures of fear-/anxiety-like behavior, these doses of nicotine and DH?E significantly reduced digging behavior in a marble burying task and 0.3 mg/kg DH?E promoted open-arm activity in the elevated plus maze. Doses of nicotine and DH?E that altered affective behavior had no effect on locomotor activity. Similar to previous reports with anxiolytic drugs, low dose nicotine and DH?E reversed SR in a CER assay, decreased digging in a marble burying assay and increased open arm activity in the elevated plus maze. This study provides evidence that inactivation of ?2*nAChRs reduces fear-like and anxiety-like behavior in rodents and suggests that smokers may be motivated to smoke in part to desensitize their ?2*nAChRs. These data further identify ?2*nAChR antagonism as a potential therapeutic strategy for relief of negative affect and anxiety.

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Nicotine stimulates ion transport via metabotropic ?4 subunit containing nicotinic ACh receptors.

Publications

Nicotine stimulates ion transport via metabotropic β4 subunit containing nicotinic ACh receptors.

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