REGULATION OF EPITHELIAL Na+ CHANNELS BY ALDOSTERONE: ROLE OF Sgk1 (original) (raw)
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Epithelial sodium channel (ENaC) in GtoPdb v.2021.2
IUPHAR/BPS Guide to Pharmacology CITE, 2021
The epithelial sodium channels (ENaC) are located on the apical membrane of epithelial cells in the kidney tubules, lung, respiratory tract, male and female reproductive tracts, sweat and salivary glands, placenta, colon, and some other organs [9, 13, 22, 21, 42]. In these epithelia, Na+ ions flow from the extracellular fluid into the cytoplasm of epithelial cells via ENaC. The Na+ ions are then pumped out of the cytoplasm into the interstitial fluid by the Na+/K+ ATPase located on the basolateral membrane [36]. As Na+ is one of the major electrolytes in the extracellular fluid (ECF), osmolarity change initiated by the Na+ flow is accompanied by a flow of water accompanying Na+ ions [6]. Thus, ENaC has a central role in regulating ECF volume and blood pressure, primarily via its function in the kidney [37]. The expression of ENaC subunits, hence its activity, is regulated by the renin-angiotensin-aldosterone system, and other factors involved in electrolyte homeostasis [37, 30]. In ...
Journal of the American Society of Nephrology, 2014
In relation to dietary Na + intake and aldosterone levels, collecting duct principal cells are exposed to large variations in Na + transport. In these cells, Na + crosses the apical membrane via epithelial Na + channels (ENaC) and is extruded into the interstitium by Na,K-ATPase. The activity of ENaC and Na,K-ATPase must be highly coordinated to accommodate variations in Na + transport and minimize fluctuations in intracellular Na + concentration. We hypothesized that, independent of hormonal stimulus, cross-talk between ENaC and Na,K-ATPase coordinates Na + transport across apical and basolateral membranes. By varying Na + intake in aldosterone-clamped rats and overexpressing g-ENaC or modulating apical Na + availability in cultured mouse collecting duct cells, enhanced apical Na + entry invariably led to increased basolateral Na,K-ATPase expression and activity. In cultured collecting duct cells, enhanced apical Na + entry increased the basolateral cell surface expression of Na,K-ATPase by inhibiting p38 kinase-mediated endocytosis of Na,K-ATPase. Our results reveal a new role for p38 kinase in mediating cross-talk between apical Na + entry via ENaC and its basolateral exit via Na,K-ATPase, which may allow principal cells to maintain intracellular Na + concentrations within narrow limits.
The epithelial sodium channel (ENaC) is intracellularly located as a tetramer
Pflugers Archiv-european Journal of Physiology, 2002
The epithelial sodium channel (ENaC) plays an important role in Na+ homeostasis by determining the Na+ transport rate in so-called end-organs such as the renal collecting duct, distal colon, salivary and sweat gland ducts. ENaC is formed by heteromultimerization of three homologous subunits, termed α, β, and γ ENaC. The number of subunits and stoichiometry remain a matter of debate. In this study, sucrose gradient analysis of Xenopus laevis oocytes expressing rENaC revealed that ENaC forms heterotetramers, when the membrane fraction was solubilized in 0.1% (wt/vol) Na-deoxycholate. However, solubilization of the membrane proteins in higher concentrations of detergents dissociated the ENaC subunits of the tetramers in dimers. Co-immunoprecipitation studies with FLAG-tagged ENaC subunits suggest that during dissociation of ENaC tetramers the composition of dimers is completely random. Glycosidase digestion studies show that the ENaC subunits are retarded in the endoplasmic reticulum (ER) and pre-Golgi, whereas only a small fraction is inserted into the plasma membrane. Immunocytochemical analysis confirmed that ENaC is primarily located intracellularly. In addition, these findings are not restricted to the oocyte expression system, since identical results were found in rabbit connecting tubule and cortical collecting duct cells in primary culture and in rabbit colon.
Membrane trafficking pathways regulating the epithelial sodium channel, ENaC
American Journal of Physiology-Renal Physiology
Renal Na+ reabsorption, facilitated by the epithelial sodium channel, ENaC, is subject to multiple forms of control to ensure optimal body blood volume and pressure through altering both ENaC population and activity at the cell surface. Here the focus is on regulating the number of ENaCs present in the apical membrane domain through pathways of ENaC synthesis and targeting to the apical membrane, as well as ENaC removal, recycling and degradation. Finally, the mechanisms by which ENaC trafficking pathways are regulated are summarised.
The Journal of Physiology, 1996
Isolated frog skin epithelium, mounted in an Ussing chamber and bathed in standard NaCl Ringer solution, recycles K+ across the basolateral membrane of principal cells through an inward-rectifier K+ channel (Kir) operating in parallel with a Na+-K+-ATPase pump. Here we report on the metabolic control of the Kir channel using patch clamping, short-circuit current measurement and enzymatic determination of cellular ATP (ATP1). 2. The constitutively active Kir channel in the basolateral membrane has the characteristics of an ATP-regulated K+ channel and is now classed as a KATP channel. In excised inside-out patches the open probability (PO) of KATP channels was reduced by ATP, with halfmaximum inhibition at an ATP1 concentration of 50 /M. 3. ATP1 measured (under normal Na+ transport conditions) with luciferin-luciferase was 1P50 + 0 23 mm (mean + S.E.M.; range, 0A4-3 3 mm, n = 11). Thus the KATP channel would be expected to be inactive in intact cells if ATPi was the sole regulator of channel activity. KATP channels which were inactivated by 1 mm ATPi in excised patches could be reactivated by addition of 100 uM ADP on the cytosolic side. When added alone, ADP blocks this channel with half-maximal inhibition at [ADPJ] > 5 mM. 4. Sulphonylureas inhibit single KATP channels in cell-attached patches as well as the total basolateral K+ current measured in frog skin epithelia perforated with nystatin on the apical side. 5. Na+-K+-ATPase activity is a major determinant of cytosolic ATP. Blocking the pump activity with ouabain produced a time-dependent increase in ATPi and reduced the open probability of KATP channels in cell-attached membranes. 6. We conclude that the ratio of ATP/ADP is an important metabolic coupling factor between the rate of Na+-K+ pumping and K+ recycling. The reabsorption of Na across principal cells of frog skin epithelium is mediated by passive entry through channels in the apical membrane and active secretion via an Na+-K+-ATPase localized in the basolateral membrane. In parallel with the Na+-K+ pump activity, K+ is recycled through a channel which was recently identified as an inward-rectifier K+ channel (Kir) localized in the basolateral membrane of principal cells (Urbach, Van Kerkhove & Harvey, 1994). The maintenance of equilibrium between transepithelial Nae absorption and K+ recycling involves a concerted action of cellular signals (cross-talk). Coupling between the apical Nae conductance and the basolateral K+ conductance has been described in frog skin and turtle and toad urinary bladder (Davis & Finn, 1982; Harvey, Thomas & Ehrenfeld, 1988; Dawson & Richards, 1990). These studies have demonstrated a role for membrane potential, pH and Ca2+ in mediating cross-talk. In tight epithelia, pHi has been shown to be a potent regulator of net sodium absorption via the pH sensitivity of apical Nae and basolateral K+
Regulation of the epithelial sodium channel by membrane trafficking
AJP: Renal Physiology, 2008
The epithelial Na+ channel (ENaC) is a major regulator of salt and water reabsorption in a number of epithelial tissues. Abnormalities in ENaC function have been directly linked to several human disease states including Liddle's syndrome, psuedohypoaldosteronism, and cystic fibrosis and may be implicated in states as diverse as salt-sensitive hypertension, nephrosis, and pulmonary edema. ENaC activity in epithelial cells is highly regulated both by open probability and number of channels. Open probability is regulated by a number of factors, including proteolytic processing, while ENaC number is regulated by cellular trafficking. This review discusses current understanding of apical membrane delivery, cell surface stability, endocytosis, retrieval, and recycling of ENaC and the molecular partners that have so far been shown to participate in these processes. We review known sites and mechanisms of hormonal regulation of trafficking by aldosterone, vasopressin, and insulin. While...
Feedback inhibition of ENaC during acute sodium loading in vivo
AJP: Renal Physiology, 2013
The epithelial Na+ channel (ENaC) is tightly regulated by sodium intake to maintain whole body sodium homeostasis. In addition, ENaC is inhibited by high levels of intracellular Na+ [Na+]i, presumably to prevent cell Na+ overload and swelling. However, it is not clear if this regulation is relevant in vivo. We show here that in rats, an acute (4 h) oral sodium load decreases whole-cell amiloride-sensitive currents ( INa) in the cortical collecting duct (CCD) even when plasma aldosterone levels are maintained high by infusing the hormone. This was accompanied by decreases in whole-kidney cleaved α-ENaC (2.6 fold), total β-ENaC (1.7 fold), and cleaved γ-ENaC (6.2 fold). In addition, cell-surface β- and γ-ENaC expression was measured using in situ biotinylation. There was a decrease in cell-surface core-glycosylated (2.2 fold) and maturely glycosylated (4.9 fold) β-ENaC and cleaved γ-ENaC (4.7 fold). There were no significant changes for other apical sodium transporters. To investigate...
The Sodium Chloride Cotransporter (NCC) and Epithelial Sodium Channel (ENaC) Associate
The Biochemical journal, 2016
The thiazide-sensitive sodium chloride cotransporter (NCC) and the Epithelial Sodium Channel (ENaC) are two of the most important determinants of salt balance and thus systemic blood pressure. Abnormalities in either result in profound changes in blood pressure. There is one segment of the nephron where these two sodium transporters are co-expressed, the second part of the Distal Convoluted Tubule. This is a key part of the aldosterone-sensitive distal nephron, the final regulator of salt handling in the kidney. Aldosterone is the key hormonal regulator for both of these proteins. Despite these shared regulators and co-expression in a key nephron segment, associations between these proteins have not been investigated. After confirming apical localization of these proteins, we demonstrated the presence of functional transport proteins and native association by Blue Native PAGE. Extensive co-immunoprecipitation experiments demonstrated a consistent interaction of NCC with alpha and ga...