Characterization of the Epithelial Sodium Channel δ-Subunit in Human Nasal Epithelium

Abstract

The epithelial sodium channel (ENaC) mediates the first step in Na+ reabsorption in epithelial cells such as kidney, colon, and airways and may consist of four homologous subunits (alpha, beta, gamma, delta). Predominantly, the alpha-subunit is expressed in these epithelia, and it usually forms functional channels with the beta- and gamma-subunits. The delta-subunit was first found in human brain and kidney, but the expression was also detected in human cell lines of lung, pancreatic, and colonic origin. When co-expressed with beta and gamma accessory subunits in heterologous systems, the two known isoforms of the delta-ENaC subunit (delta1 and delta2) can build amiloride-sensitive Na+ channels. In the present study we demonstrate the expression and function of the delta-subunit in human nasal epithelium (HNE). We cloned and sequenced the full-length cDNA of the delta-ENaC subunit and were able to show that in nasal tissue at least isoform 1 is expressed. Furthermore, we performed Western blot analyses and compared the cell surface expression of the delta-subunit with the classically expressed alpha-subunit by using immunofluorescence experiments. Thereby, we could show that the quantity of both subunits is almost similar. In addition, we show the functional expression of the delta-ENaC subunit with measurements in modified Ussing chambers, and demonstrate that in HNE a large portion of the Na+ transport is mediated by the delta-ENaC subunit. Therefore, we suppose that the delta-subunit may possess an important regulatory function and might interact with other ENaC subunits or members of the DEG/ENaC family in the human respiratory epithelium.

Expression and function of the epithelial sodium channel δ-subunit in human respiratory epithelial cells in vitro

“…In our hands, Evans blue reduced currents across both NCI-H441 and ATI-like cell monolayers, which was consistent with previous observations in oocytes [48] and HNE cells [3], but exhibited concentration-dependent stimulatory effects on the I SC in Calu-3 cells.…”

“…Only a single publication, however, reported the use of these compounds as modulators of δ-ENaC function in an organotypic in vitro model, i.e. in human nasal epithelial (HNE) cells [3]. No functional evidence has yet been provided for other respiratory epithelial cell types, in particular NCI-H441 cells, for which δ-ENaC expression has been reported repeatedly [27, 37, 38].…”

“…Moreover, Bangel-Ruland et al [3] demonstrated the presence of δ-ENaC in primary human nasal epithelial cells (HNE). Since δ-ENaC physically interacts with α-and γ-subunits in NCI-H441 cells, and δαβγ-channels, heterologously expressed in X. laevis oocytes, displayed biophysical and pharmacological characteristics (i.e.…”

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na+ Self-Inhibition of Epithelial Na+ Channels

“…have been functionally detected in human nasal epithelial cells (36). We previously found that CPT-cGMP activated dabg ENaC in oocytes (26).…”

Characterization of a novel splice variant of δ ENaC subunit in human lungs

“…This is supported by a very recent finding that ␦ ENaC channels contributed to ϳ50% of amiloride-sensitive salt transport across primary human nasal epithelial cells (3). We and others (3,29,37) have recently shown that an additional ENaC subunit (termed ␦ ENaC) may account for diverse observations in the biophysical properties of native epithelial Na ϩ channels. Biophysical and pharmacological studies such as these in Xenopus oocytes have shown that heteromultimeric ␦␤␥ ENaC channels exhibited high selectivity for Na ϩ over Li ϩ ions, less amiloride sensitivity than ␣␤␥ ENaC (25, 36, 44), and were regulated by changes in extracellular pH (24,36,53).…”