title: Angiotensin II increases activity of the epithelial Na+ channel (ENaC) in distal nephron additively to aldosterone.
abstract: Dietary salt intake controls epithelial Na+ channel (ENaC)-mediated Na+ reabsorption in the distal nephron by affecting status of the renin-angiotensin-aldosterone system (RAAS). Whereas regulation of ENaC by aldosterone is generally accepted, little is known about whether other components of RAAS, such as angiotensin II (Ang II), have nonredundant to aldosterone-stimulatory actions on ENaC. We combined patch clamp electrophysiology and immunohistochemistry in freshly isolated split-opened distal nephrons of mice to determine the mechanism and molecular signaling pathway of Ang II regulation of ENaC. We found that Ang II acutely increases ENaC Po, whereas prolonged exposure to Ang II also induces translocation of α-ENaC toward the apical membrane in situ. Ang II actions on ENaC Po persist in the presence of saturated mineralocorticoid status. Moreover, aldosterone fails to stimulate ENaC acutely, suggesting that Ang II and aldosterone have different time frames of ENaC activation. AT1 but not AT2 receptors mediate Ang II actions on ENaC. Unlike its effect in vasculature, Ang II did not increase [Ca2+]i in split-opened distal nephrons as demonstrated using ratiometric Fura-2-based microscopy. However, application of Ang II to mpkCCDc14 cells resulted in generation of reactive oxygen species, as probed with fluorescent methods. Consistently, inhibiting NADPH oxidase with apocynin abolished Ang II-mediated increases in ENaC Po in murine distal nephron. Therefore, we concluded that Ang II directly regulates ENaC activity in the distal nephron, and this effect complements regulation of ENaC by aldosterone. We propose that stimulation of AT1 receptors with subsequent activation of NADPH oxidase signaling pathway mediates Ang II actions on ENaC.
authors.affiliation: Department of Integrative Biology and Pharmacology, the University of Texas Health Science Center, Houston, Texas 77030.
authors.forename: Mykola
authors.initials: M
authors.lastname: Mamenko
authors.affiliation: Department of Integrative Biology and Pharmacology, the University of Texas Health Science Center, Houston, Texas 77030.
authors.forename: Oleg
authors.initials: O
authors.lastname: Zaika
authors.affiliation: Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226; Institute of Cytology, Russian Academy of Sciences, 194064 St. Petersburg, Russia.
authors.forename: Daria V
authors.initials: DV
authors.lastname: Ilatovskaya
authors.affiliation: Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors.forename: Alexander
authors.initials: A
authors.lastname: Staruschenko
authors.affiliation: Department of Integrative Biology and Pharmacology, the University of Texas Health Science Center, Houston, Texas 77030. Electronic address: oleh.m.pochynyuk@uth.tmc.edu.
authors.forename: Oleh
authors.initials: O
authors.lastname: Pochynyuk
mesh_terms: D000450:Aldosterone / Q000494:pharmacology*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D019255:NADPH Oxidases / Q000378:metabolism; D009399:Nephrons / Q000187:drug effects* / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D012084:Renin-Angiotensin System / Q000187:drug effects; D012964:Sodium / Q000378:metabolism
chemical_list: D053503:Epithelial Sodium Channels; D017382:Reactive Oxygen Species; D044140:Receptor, Angiotensin, Type 1; D000804:Angiotensin II; D000450:Aldosterone; D012964:Sodium; D019255:NADPH Oxidases; D002118:Calcium
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