Diversity and regulation of amiloride-sensitive Na+ channels

Benos, Dale J.; Awayda, Mouhamed S.; Berdiev, Bakhrom K.; Bradford, A. L.; Fuller, Catherine M.; Senyk, Oksana; Ismailov, Iskander I.

doi:10.1038/ki.1996.237

Cited by 41 publications

(34 citation statements)

References 27 publications

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“…While a role for adrenal steroids is unlikely, angiotensin II and adrenocorticotropin hormone (ACTH) are intriguing potential moderators of chorda tympani responsiveness. ENaC activity is modulated by G-protein linked second messenger systems in the non-taste epithelium (Benos et al 1996, Ismailov et al 1995 and angiotensin II and ACTH can influence the activity of these second messenger pathways (Edwards et al 1993, Underwood et al 1989. This, in conjunction with that fact that plasma levels of angiotensin II and ACTH are elevated in sodium depleted rats make it possible that these hormones may also regulate ENaC activity on the tongue.…”

Section: Proposed Model and Remaining Questionsmentioning

confidence: 99%

Richter and sodium appetite: From adrenalectomy to molecular biology

Krause

Sakai

2007

Appetite

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Nearly three-quarters of a century ago, Curt Richter removed the adrenal glands from rats and noted that the animal's vitality was dependent on its increased consumption of sodium chloride. In doing so, Richter revealed an innate behavioral mechanism that serves to maintain the hydromineral balance of an animal faced with sodium deficit. This experiment and others like it, led to the development of a field of research devoted to the investigation of salt appetite. The following is a discussion of how Richter's initial observations gave birth to an evolving field that incorporates multiple approaches to examine the drive to consume sodium. KeywordsSalt appetite; Angiotensin; Aldosterone; Corticosterone; Richter The Discovery of Salt AppetiteAt the time that Richter began his career at Johns Hopkins University much of the research examining ingestive behavior focused on the responses of individual organs or closely coordinated systems. Richter's pioneering work initiated a fundamental paradigm shift that moved the focus to adaptations of the organism as a whole. Specifically, he was interested in changes in behavior that compensated for perturbations in the internal environment. His approach toward investigation of such behaviors was as thorough as it was fundamental. Richter manipulated diet, interfered with the nervous system, and removed or replaced glandular secretions in attempt to understand the nutritional, neural, and endocrine signals that contribute to behavior.Richter created disturbances in the nutritional or mineral content of the internal environment with dietary deficiency. Subsequently, "self selection" experiments were performed where choices of different minerals and nutrients were presented for consumption. More often than not, animals would consume minerals and nutrients in amounts that would alleviate their experimentally-induced deficiencies. One of the most striking behaviors that Richter observed was that of rats voluntarily ingesting salt when faced with sodium deficit. Sodium chloride was removed from the rats' food and they were given access to water and 3 % NaCl solution. The intake of the NaCl solution was approximately 1% of the total diet, which remarkably, is the

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Section: Proposed Model and Remaining Questionsmentioning

confidence: 99%

Richter and sodium appetite: From adrenalectomy to molecular biology

Krause

Sakai

2007

Appetite

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“…To test this hypothesis, we examined the effect of the diuretic amiloride and its analog benzamil. These agents inhibit most known DEG͞ENaC channels (3,31). Moreover, their application into the liquid-filled lung of embryonic guinea pigs delayed lung liquid clearance at birth, causing hypoxemia and respiratory distress (8).…”

Section: Distinct Ppk Gene Expression Patterns In the Adult Tracheal mentioning

confidence: 99%

Drosophila DEG/ENaC pickpocket genes are expressed in the tracheal system, where they may be involved in liquid clearance

Liu

Johnson

Welsh

2003

Proc. Natl. Acad. Sci. U.S.A.

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The Drosophila tracheal system and mammalian airways are branching networks of tubular epithelia that deliver oxygen to the organism. In mammals, the epithelial Na ؉ channel (ENaC) helps clear liquid from airways at the time of birth and removes liquid from the airspaces in adults. We tested the hypothesis that related Drosophila degenerin (DEG)͞ENaC family members might play a similar role in the fly. Among 16 Drosophila DEG͞ENaC genes, called pickpocket (PPK) genes, we found 9 expressed in the tracheal system. By in situ hybridization, expression appeared in late-stage embryos after tracheal tube formation, with individual PPK genes showing distinct temporal and spatial expression patterns as development progressed. Promoters for several PPK genes drove reporter gene expression in the larval and adult tracheal systems. Adding the DEG͞ENaC channel blocker amiloride to the medium inhibited liquid clearance from the trachea of first instar larvae. Moreover, when RNA interference was used to silence PPK4 and PPK11, larvae failed to clear tracheal liquid. These data suggest substantial molecular diversity of DEG͞ENaC channel expression in the Drosophila tracheal system where the PPK proteins likely play a role in Na ؉ absorption. Extensive similarities between Drosophila and mammalian airways offer opportunities for genetic studies that may decipher further the structure and function of DEG͞ENaC proteins and development of the airways.trachea ͉ Na ϩ channel ͉ absorption ͉ epithelia ͉ amiloride C omplex multicellular organisms require an elaborate oxygen delivery system to meet tissue metabolic demands. In mammalian lung, a network of branching epithelial tubes carries oxygen to the alveoli, where it diffuses into blood to be distributed to the tissues. Drosophila melanogaster also possesses a network of branching epithelial tubes through which oxygen diffuses to reach cells throughout the organism (1). In addition to their functional similarity, the growth factors and transcription factors controlling branching morphogenesis in mammalian airways and the fly tracheal system share numerous features (2). Moreover, at specific points in development, both systems must convert from liquid-to air-filled tubules. In mammals, this conversion occurs at birth, when the epithelium actively absorbs salt and hence liquid from the airways. In Drosophila, this conversion occurs 2 h before larvae emerge, also by active epithelial absorption (1).In mammalian airways, the epithelial Na ϩ channel (ENaC), composed of ␣-, ␤-, and ␥-ENaC subunits, contributes to salt and liquid absorption (3, 4). Striking evidence for this role came from mice bearing targeted disruptions of ENaC genes. Mice with a disrupted ␣-ENaC gene died shortly after birth, because they failed to clear lung liquid, and mice with disrupted ␤-or ␥-ENaC genes showed delayed lung liquid clearance (5-7). In humans, impaired ENaC activity may contribute to neonatal respiratory distress syndrome (8). ENaC-dependent salt and liquid absorption may also help clear pulmonary ed...

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“…The extracellular domain plays a role in subunit interaction, targeting channels to the plasma membrane and channel gating (4,(7)(8)(9)11). The COOH terminus plays an important role in localizing ENaC to the apical membrane, and it contains an NPXY motif that is important in the endocytic retrieval of the channel from the plasma membrane (1)(2)(3)(4)(12)(13)(14)(15). For example, in Liddle's syndrome mutations and/or deletions of the NPXY motif in ␤-or ␥-ENaC reduces subunit ubiquitination and endocytic retrieval of ENaC from the plasma membrane.…”

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confidence: 99%

“…Amino acid sequence analysis and biochemical studies suggest that the ENaC subunits have cytoplasmic NH 2 and COOH termini, two hydrophobic transmembrane domains (M1 and M2) and a large extracellular domain (4 -8). Several lines of evidence suggest that the ␣-, ␤-, and ␥-subunits interact to form a heteromultimeric channel complex and that this complex is required for maximum Na ϩ currents (4 -8).…”

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The NH2 Terminus of the Epithelial Sodium Channel Contains an Endocytic Motif

Chalfant¹,

Denton²,

Langloh³

et al. 1999

Journal of Biological Chemistry

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An epithelial sodium channel (ENaC) is composed of three homologous subunits: ␣, ␤, and ␥. To elucidate the function of the cytoplasmic, NH 2 terminus of rat ENaC (rENaC) subunits, a series of mutant cDNAs was constructed and the cRNAs for all three subunits were expressed in Xenopus oocytes. Amiloride-sensitive Na ؉ currents (I Na ) were measured by the two-electrode voltage clamp technique. Deletion of the cytoplasmic, NH 2 terminus of ␣ (⌬2-109), ␤ (⌬2-49), or ␥-rENaC (⌬2-53) dramatically reduced I Na . A series of progressive, NH 2 -terminal deletions of ␣-rENaC were constructed to identify motifs that regulate I Na . Deletion of amino acids 2-46 had no effect on I Na : however, deletion of amino acids 2-51, 2-55, 2-58, and 2-67 increased I Na by ϳ4-fold. By contrast, deletion of amino acids 2-79, 2-89, 2-100, and 2-109 eliminated I Na . To evaluate the mechanism whereby ⌬2-67-␣-rENaC increased I Na , single channels were evaluated by patch clamp. The single-channel conductance and open probability of ␣,␤,␥-rENaC and ⌬2-67-␣,␤,␥-rENaC were similar. However, the number of active channels in the membrane increased from 6 ؎ 1 channels per patch with ␣,␤,␥-rENaC to 11 ؎ 1 channels per patch with ⌬2-67-␣,␤,␥-rENaC. Laser scanning confocal microscopy confirmed that there were more ⌬2-67-␣,␤,␥-rENaC channels in the plasma membrane than ␣,␤,␥-rENaC channels. Deletion of amino acids 2-67 in ␣-rENaC reduced the endocytic retrieval of channels from the plasma membrane and increased the half-life of the channel in the membrane from 1.1 ؎ 0.2 to 3.5 ؎ 1.1 h. We conclude that the cytoplasmic, NH 2 terminus of ␣-, ␤-, and ␥-rENaC is required for channel activity. The cytoplasmic, NH 2 terminus of ␣-rENaC contains two key motifs. One motif regulates the endocytic retrieval of the channel from the plasma membrane. The second motif is required for channel activity.An amiloride-sensitive, epithelial sodium channel (ENaC) 1 mediates Na ϩ transport across the apical membrane of a variety of epithelia including the kidney, lung, and intestine and, thereby, plays a vital role in maintaining Na ϩ and fluid homeostasis (1-4). ENaC is composed of three subunits: ␣, ␤, and ␥ (5, 6). The expression of the ␣ subunit in Xenopus oocytes produces very small currents, and the expression of ␤ and/or ␥ subunits generates no current (5, 6). However, coexpression of ␣-, ␤-, and ␥-rENaC produces large Na ϩ currents in oocytes (5, 6). The ENaC subunits are members of a growing family of ion channels that include the FMRFamide-gated Na ϩ channel, Na ϩ channels in brain (BNC1 and BNC2), and the degenerins of Caenorhabditis elegans that encode mechanosensitive channels (e.g. DEG-1, MEC-4, and MEC-10) (4, 7).Amino acid sequence analysis and biochemical studies suggest that the ENaC subunits have cytoplasmic NH 2 and COOH termini, two hydrophobic transmembrane domains (M1 and M2) and a large extracellular domain (4 -8). Several lines of evidence suggest that the ␣-, ␤-, and ␥-subunits interact to form a heteromultimeric channel complex and that this c...

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Diversity and regulation of amiloride-sensitive Na+ channels

Cited by 41 publications

References 27 publications

Richter and sodium appetite: From adrenalectomy to molecular biology

Richter and sodium appetite: From adrenalectomy to molecular biology

Drosophila DEG/ENaC pickpocket genes are expressed in the tracheal system, where they may be involved in liquid clearance

The NH2 Terminus of the Epithelial Sodium Channel Contains an Endocytic Motif

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