Oxidized Glutathione Increases Delta-Subunit Expressing Epithelial Sodium Channel Activity in Xenopus laevis Oocytes.

Abstract

Epithelial sodium channels (ENaC) are heterotrimeric structures, made up of α, β, and γ subunits, and play an important role in maintaining fluid homeostasis. When δ-ENaC subunits are expressed in place of (or in addition to) the α-ENaC subunit alongside β- and γ- subunits, fundamental changes in the biophysical properties of ENaC can be observed. Using human ENaC cRNA constructs and the Xenopas laevis oocyte expression system, we show that oxidized glutathione (GSSG) differently effects αβγ-ENaC and αβγ-ENaC current. GSSG (400 μM) significantly decreased normalized whole cell current in oocytes expressing αβγ-ENaC, and conversely increased whole cell current in δ1βγ-ENaC and δ2βγ-ENaC expressing oocytes. GSSG treatment increased current in oocytes expressing all four subunits. Western blot and PCR analysis show that human small airway epithelial cells (hSAEC) express canonical αβγ-subunits alongside δ-ENaC subunits. Differences in single channel responses to GSSG in hSAECs indicate that airway epithelia redox sensitivity may depend on whether δ- or α- subunits assemble in the membrane. In silico analysis predict that six Cys amino acids in the δ-ENaC extracellular loop, and a single Cys in the N-terminal domain, are susceptible to post-translational modification by GSSG. Additional studies are needed to better understand the molecular regulation and pathophysiological roles of oxidized glutathione and δ-ENaC in lung disorders.