Regulation of the epithelial Na⁺channel by endothelin-1 in rat collecting duct

Abstract

We used patch-clamp electrophysiology to investigate regulation of the epithelial Na ϩ channel (ENaC) by endothelin-1 (ET-1) in isolated, split-open rat collecting ducts. ET-1 significantly decreases ENaC open probability by about threefold within 5 min. ET-1 decreases ENaC activity through basolateral membrane ETB but not ETA receptors. In rat collecting duct, we find no role for phospholipase C or protein kinase C in the rapid response of ENaC to ET-1. ET-1, although, does activate src family tyrosine kinases and their downstream MAPK1/2 effector cascade in renal principal cells. Both src kinases and MAPK1/2 signaling are necessary for ET-1-dependent decreases in ENaC open probability in the split-open collecting duct. We conclude that ET-1 in a physiologically relevant manner rapidly suppresses ENaC activity in native, mammalian principal cells. These findings may provide a potential mechanism for the natriuresis observed in vivo in response to ET-1, as well as a potential cause for the salt-sensitive hypertension found in animals with impaired endothelin signaling.salt-sensitive hypertension; systemic blood pressure ENDOTHELIN-1 (ET-1) is a powerful vasoconstricting peptide hormone that is an important regulator of systemic blood pressure (53). Independent of its vascular effects, ET-1 also affects renal Na ϩ and water handling favoring natriuresis and diuresis. While circulating ET-1 arises from endothelial cells, local ET-1 systems also exist. For instance in the kidney, the collecting duct produces significant amounts of 25,38,51). ET-1 targets cells through two distinct receptor subtypes, ET A and ET B (32, 41). Renal collecting duct cells have both types of receptors and are able to bind 49,50). Thus, collecting duct-derived ET-1, acting in a paracrine/ autocrine manner, is an important regulator of renal Na ϩ handling (2,20,26,42).Regulated Na ϩ reabsorption in the renal collecting duct, in part, controls blood pressure. Here, activity of the aldosteronesensitive epithelial Na ϩ channel (ENaC) is limiting for Na ϩ transport (reviewed in Refs. 19,30,31). Dysfunction and inappropriate regulation of ENaC consequently result in improper renal Na ϩ handling and thus, blood pressure disorders. For instance, gain of ENaC function in rodents and humans is causative for hypertension associated with the hallmarks of low plasma renin activity and aldosterone levels (1,22,23,45,46). Amiloride, an ENaC blocker, ameliorates this hypertension.Spotting lethal (sl) rats have a naturally occurring null mutation of ET B (17). These rats, when rescued from lethal intestinal aganglionosis by directed ET B transgene expression in the enteric nervous system, are particularly sensitive to DOCA and salt-induced hypertension (18,33,34). Similarly, mice with collecting duct-specific knockout of the ET B receptor have elevated blood pressure that further increases with high salt feeding (20). Collecting duct-specific ET-1 knockout, moreover, leads to hypertension exacerbated by high salt (2, 42). Plasma renin activity and aldoste...

Endothelin-1 Inhibits the Epithelial Na+ Channel through βPix/14-3-3/Nedd4-2

“…[17][18][19] Renal tubular cells may secrete ET-1 themselves, which could regulate sodium transport in the kidney under physiologic and pathologic conditions. Our observations that ET-1 decreases ENaC activity in freshly isolated principal cells of the rat CD, polarized mouse mpkCCD c14 cells, and CHO cells transiently expressed with ENaC subunits, are consistent with those data.…”

“…Further studies revealed that basal Src family kinase activity strongly regulates ENaC inhibition. 18 Bugaj et al 19 recently demonstrated in native rat cortical collecting duct (CCD) principal cells that ET-1 dynamically decreases ENaC open probability via ET B receptors and that subsequent intracellular pathways involved Src tyrosine kinase activity and MAPK1/2 signaling. Furthermore, it was recently shown that aldosterone modulates steroid receptor binding to the ET-1 gene.…”

Aldosterone Modulates Steroid Receptor Binding to the Endothelin-1 Gene (edn1)

“…These same processes are also influenced by aldosterone. However, renal ET-1 is a well documented natriuretic peptide that directly blocks sodium transport in the tubule collecting duct (28,(33)(34)(35)(36)(37). The physiological importance of collecting duct ET-1 is emphasized by the fact that collecting duct cell-specific edn1 knock-out mice exhibit saltsensitive hypertension (31).…”

New insights into sodium transport regulation in the distal nephron: Role of G-protein coupled receptors

“…As opposed to finding in the cTAL (see above), ET-1 triggers the inhibition of the AVP-stimulated chloride transport in the CCD through PKC activation [105] . In addition to counteracting the effects of AVP, ET-1 also inhibits ENaC activity through both MAP kinase-dependent and NO-dependent pathways [107] . ETB activation has functional consequences on IC.…”