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2021, IUPHAR/BPS Guide to Pharmacology CITE
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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 ...
Acta Pharmacologica Sinica, 2011
The topology and physiology of ENaC Since 1994, when ENaC was initially cloned from the rat colon [8] , the biophysical properties and molecular structure of ENaC have been extensively studied. ENaC consists of at least three subunits including α, β, and γ, each of which possesses two transmembrane domains, a large extracellular loop, a cytoplasmic C-terminal domain and a N-terminal domain. All three subunits are required to form a functional α-, β-, γ-ENaC channel complex (Figure 1) [8-15]. ENaC belongs to a member of the ENaC/Deg superfamily of ion channels that are responsible for sodium transport. The channel is typically located at the apical membrane of epithelial tissues throughout the body, including the colon, the sweat glands, the salivary duct, the airway, and the cortical collecting duct (CCD) of the kidney,
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...
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.
American Journal of Physiology-Renal Physiology, 2012
Amiloride-sensitive epithelial Na+ channels (ENaCs) can be formed by different combinations of four homologous subunits, named α, β, γ, and δ. In addition to providing an apical entry pathway for transepithelial Na+ reabsorption in tight epithelia such as the kidney distal tubule and collecting duct, ENaCs are also expressed in nonepithelial cells, where they may play different functional roles. The δ-subunit of ENaC was originally identified in humans and is able to form amiloride-sensitive Na+ channels alone or in combination with β and γ, generally resembling the canonical kidney ENaC formed by α, β, and γ. However, δ differs from α in its tissue distribution and channel properties. Despite the low sequence conservation between α and δ (37% identity), their similar functional characteristics provide an excellent model for exploring structural correlates of specific ENaC biophysical and pharmacological properties. Moreover, the study of cellular mechanisms modulating the activity ...
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...
Clinical and Experimental Pharmacology and Physiology, 2008
Journal of Biological Chemistry, 2010
2 The abbreviations used are: ENaC, epithelial Na ϩ channel; NCC, Na ϩ /Cl Ϫcoupled cotransporter; ASIC, acid-sensing ion channel; ERC, ENaC regulatory complex.
Cellular Signalling, 1989
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.
Frontiers in Cardiovascular Medicine
A major regulator of blood pressure and volume homeostasis in the kidney is the epithelial sodium channel (ENaC). ENaC is composed of alpha(α)/beta(β)/gamma(γ) or delta(δ)/beta(β)/gamma(γ) subunits. The δ subunit is functional in the guinea pig, but not in routinely used experimental rodent models including rat or mouse, and thus remains the least understood of the four subunits. While the δ subunit is poorly expressed in the human kidney, we recently found that its gene variants are associated with blood pressure and kidney function. The δ subunit is expressed in the human vasculature where it may influence vascular function. Moreover, we recently found that the δ subunit is also expressed human antigen presenting cells (APCs). Our studies indicate that extracellular Na+ enters APCs via ENaC leading to inflammation and salt-induced hypertension. In this review, we highlight recent findings on the role of extra-renal ENaC in inflammation, vascular dysfunction, and blood pressure mod...
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