AbstractThe 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 non-voltage 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).C. eleganshas 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 theC. elegansDEG/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 fiveC. elegansDEG/ENaC/ASICs (DEGT-1, DEL-1, UNC-8, MEC-10 and MEC-4) that are co-expressed in mechanosensory neurons and expressed gain-of-function‘d’mutant isoforms inXenopus laevisoocytes. 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 analogs. 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.SummaryAnimal physiology depends on degenerin, epithelial sodium, and acid-sensing ion channels (DEG/ENaC/ASICs). By measuring the sensitivity of threeC. elegansDEG/ENaC/ASICs to five amiloride analogs and five NSAIDs, we show that individual channels have distinct pharmacological footprints.
Nonsteroid Anti-Inflammatory Drugs Inhibit Both the Activity and the Inflammation-Induced Expression of Acid-Sensing Ion Channels in Nociceptors
