ACID SENSING ION CHANNEL‐2 LOCALIZES WITH α‐ AND γ‐, BUT NOT β‐ENAC SUBUNITS IN CILIATED AIRWAYS

Abstract

The epithelial sodium channel (ENaC) and Acid‐sensing ion channels (ASIC) are members of a superfamily of channels that play a significant role in transepithelial cation transport. The protein structure of the subunits that form these channels share great similarity, with two transmembrane segments (TM1 and TM2) and a large extracellular component. ENaC subunits (α, β, γ and δ) have been identified in airways. However, the stoichiometry of the subunits that composed the ENaC channel remains elusive. ASIC2 expression has been reported in ciliated cells of trachea and nasal septum. Previous studies suggested that ENaC subunits and ASIC may form a functional hybrid of non‐selective cation channels (1–4). Herein, we hypothesized that ASIC2 is expressed in porcine airways and Na+ transport can be modulated by hybrid channels composed of ASIC2 and ENaC subunits. We obtained small pieces of peripheral porcine lung tissue of approximately 0.5 cm3 and pieces of trachea of approximately 0.5 cm2 that were dissected and immediately snap‐frozen at −80°C. Serial tissue sections (7 μm thick) containing cross‐sections of small airways (diameters 0.5 – 1 mm) were used for immunohistochemistry. We used polyclonal antibodies directed to ASIC2, α‐, β‐ and γ‐subunits of ENaC as well as monoclonal antibodies directed to β‐Tubulin and ZO1, the tight junction protein. Confocal microscopic analysis demonstrated that in distal airways ASIC2 and ENaC subunits were mainly localized in airway ciliated cells. ASIC2 was found distributed at the base of the multicilia, with a distribution similar to that observed for α‐ and γ‐ENaC subunits. In contrast, a strong signal for β‐ENaC subunit was observed along the cilia in a restricted group of airway ciliated cells. In proximal airways, ASIC2 signal was also identified at the base of the multicilia of ciliated cells, similar to the distribution of α‐ and γ‐ENaC subunits. Our data suggest that ASIC2 could combine with α‐ and γ‐ENaC subunits to form hybrids of non‐selective cation channels as previously indicated (1–4), and participate in mucociliary clearance, regulation of airway surface liquid volume and composition.Support or Funding InformationSupported by the Cystic Fibrosis Research Inc., and The Nancy Olmsted Trust for Pediatric Pulmonology.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.