Multiple tetrodotoxin(TTX)‐sensitive NaV1 channels regulate action potential initiation in the nerve terminals of vagal nodose C‐fibers innervating the esophagus.
Authors: Kollarik Marian , Pavelkova Nikoleta , McDermott Jeff S. , Krajewski Jeffrey L. , Ru Fei 
Published: June 2021

Vagal afferent C‐fibers innervating the esophagus detect inflammatory and noxious stimuli and contribute to dysregulation of esophageal reflexes and sensations in diseases. The knowledge of voltage‐gated sodium channels (NaV1 subunits) regulating action potential initiation in the nerve terminal of esophageal C‐fibers would aid development of therapies aimed at inhibiting unwanted activation of these nociceptors. Extracellular single fiber recordings were made from the neurons in vagal nodose ganglia projecting mechanosensitive C‐fibers into the esophagus in the isolated vagally innervated guinea pig esophagus preparation. The drugs were perfused through the esophageal lumen (mucosa was removed to facilitate diffusion into the muscle wall containing nerve terminals) in order to allow the drug access to the nerve terminals in the esophageal wall but not to their conducting axons in the laryngeal recurrent and vagus nerves. Esophageal distention with 60–100mmHg (20s) was used as a mechanical stimulus. Single cell RT‐PCR was performed on nodose neurons retrogradely labeled from the esophagus. Mechanical response to esophageal distention in nodose C‐fibers was highly reproducible (two consecutive control distentions evoked 62±5 and 61±4 action potentials, respectively, n=39). TTX 0.1–1μM completely abolished mechanical response in 85%(24/28) C‐fibers. In the remaining 4 C‐fibers only approximately 30% of the mechanical response persisted and was abolished by 1mM lidocaine. scRT‐PCR revealed various combinations of TTX‐sensitive NaV1 subunits NaV1.7, 1.2, 1.6, 1.1 and 1.3 in the nodose TRPV1‐positive (C‐fiber) neurons traced from the esophagus. The NaV1.7 blocker PF‐05089771 0.3–30μM dose‐dependently inhibited mechanical response (n=4). At 3μM PF‐05089771 the response was inhibited by 40±8% (P<0.05). Another NaV1.7 blocker, Compound 801 (J Pharmacol Exp Ther. 361:172–80) also dose‐dependently inhibited mechanical response (n=8). At 1μM Compound 801 the response was inhibited by 39±8% (P<0.05). In the concentrations 10‐fold of those needed to completely block guinea pig NaV1.7 PF‐05089771 30μM and Compound 801 10μM inhibited mechanical response by 60+9% (N=4, P<0.05) and 52±12% (N=8, P<0.01), respectively, showing a robust (>40%) NaV1.7‐independet component of nodose C‐fiber mechanical response. NaV1.1, 1.2 and 1.3 group blocker ICA‐121431 (0.1–10μM) dose‐dependently inhibited mechanical response (N=4). At 1μM ICA‐121431 the response was inhibited by 31±6% (P<0.05). Combination of Compound 801 10μM and ICA‐121431 10μM nearly abolished mechanical response (inhibition by 91±5%, N=7, P<0.01). We conclude that multiple TTX‐sensitive NaV1 channels regulate action potential initiation in the nerve terminals of vagal nodose C‐fibers innervating the esophagus.Support or Funding InformationSupported by Eli Lilly and SPARC DK116311.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.