DEG/ENaC/ASIC channels vary in their sensitivity to anti-hypertensive and non-steroidal anti-inflammatory drugs

Abstract

The degenerin channels, epithelial sodium channels, and acid-sensing ion channels (DEG/ENaC/ASICs) play important roles in sensing mechanical stimuli, regulating salt homeostasis, and responding to acidification in the nervous system. They have two transmembrane domains separated by a large extracellular domain and are believed to assemble as homomeric or heteromeric trimers. Based on studies of selected family members, these channels are assumed to form nonvoltage-gated and sodium-selective channels sensitive to the anti-hypertensive drug amiloride. They are also emerging as a target of nonsteroidal anti-inflammatory drugs (NSAIDs). Caenorhabditis elegans has more than two dozen genes encoding DEG/ENaC/ASIC subunits, providing an excellent opportunity to examine variations in drug sensitivity. Here, we analyze a subset of the C. elegans DEG/ENaC/ASIC proteins to test the hypothesis that individual family members vary not only in their ability to form homomeric channels but also in their drug sensitivity. We selected a panel of C. elegans DEG/ENaC/ASICs that are coexpressed in mechanosensory neurons and expressed gain-of-function or d mutants in Xenopus laevis oocytes. We found that only DEGT‑1d, UNC‑8d, and MEC‑4d formed homomeric channels and that, unlike MEC‑4d and UNC‑8d, DEGT‑1d channels were insensitive to amiloride and its analogues. As reported for rat ASIC1a, NSAIDs inhibit DEGT‑1d and UNC‑8d channels. Unexpectedly, MEC‑4d was strongly potentiated by NSAIDs, an effect that was decreased by mutations in the putative NSAID-binding site in the extracellular domain. Collectively, these findings reveal that not all DEG/ENaC/ASIC channels are amiloride-sensitive and that NSAIDs can both inhibit and potentiate these channels.

Physiological insight into the conserved properties of Caenorhabditis elegans acid‐sensing degenerin/epithelial sodium channels

“…Previous research has measured an internal Na + concentration of 14 mM for ENaC‐expressing oocytes (Kusche‐Vihrog et al., 2009 ), similar to other sodium channels at high Na + concentrations (Greeff & Kuhn, 2000 ). However, in contrast to ENaCs, which are sodium channels, the mammalian ASICs, the mollusc FaNaCs and C. elegans DEG/ENaCs show a high degree of variability in their ion permeability, especially for K + but also for divalent cations (Fechner et al., 2021 ; Grunder & Chen, 2010 ; Kashlan & Kleyman, 2011 ; Lingueglia et al., 1997 ; Vallee et al., 2021 ; Yang et al., 2017 ). As the Nernst equation only considers a single permeant ion, we used a modified Goldmann–Hodgkin–Katz equation to capture the permeability of our novel acid‐sensing DEG/ENaCs to monovalent cations more accurately.…”

“…This hypothesis has received attention since ASIC2 is upregulated in patients with multiple sclerosis, an inflammatory neurodegenerative disease, and pharmacological blocking of ASICs can lessen clinical symptoms of inflammation and neuronal degeneration (Fazia et al., 2019 ; Friese et al., 2007 ). ASICs (and C. elegans DEG/ENaCs) are also targets of diverse non‐steroidal anti‐inflammatory drugs (NSAIDs) (Fechner et al., 2021 ; Voilley, 2004 ; Voilley et al., 2001 ), highlighting their importance as targets for treating pain and inflammation (Dulai et al., 2021 ). Finally, ASICs could offer potential as targets for anti‐helminthic drugs.…”

The diverse functions of the DEG/ENaC family: linking genetic and physiological insights

“…Their action is highly isoform specific; ASIC1b and ASIC2a are unaffected by most NSAIDs, while ASIC3 is inhibited by salicylic acid and diclofenac and ASIC1a is inhibited by flurbiprofen and ibuprofen (Voilley et al 2001). NSAIDs also act on C. elegans DEG/ENaCs (Fechner et al 2021), further illustrating the likely structural conservation between nematode and vertebrate channels.…”

“…NSAIDs also act on C. elegans DEG/ENaCs (Fechner et al. 2021 ), further illustrating the likely structural conservation between nematode and vertebrate channels.…”

“…The DEG/ENaC channels show a diversity in ion selectivity and permeability; while many are Na + -selective, some are also permeable to K + or Ca 2+ , and some invertebrate members exhibit a greater relative selectivity for other cations than Na + (Dürrnagel et al 2012;Fechner et al 2021;Kaulich et al 2022b;Wang et al 2008;further reviewed in Vallee et al 2021).…”