title: The epithelial sodium channel (ENaC) establishes a trafficking vesicle pool responsible for its regulation.
abstract: The epithelial sodium channel (ENaC) is the rate-limiting step for sodium reabsorption across tight epithelia. Cyclic-AMP (cAMP) stimulation promotes ENaC trafficking to the apical surface to increase channel number and transcellular Na(+) transport. Removal of corticosteroid supplementation in a cultured cortical collecting duct cell line reduced ENaC expression. Concurrently, the number of vesicles trafficked in response to cAMP stimulation, as measured by a change in membrane capacitance, also decreased. Stimulation with aldosterone restored both the basal and cAMP-stimulated ENaC activity and increased the number of exocytosed vesicles. Knocking down ENaC directly decreased both the cAMP-stimulated short-circuit current and capacitance response in the presence of aldosterone. However, constitutive apical recycling of the Immunoglobulin A receptor was unaffected by alterations in ENaC expression or trafficking. Fischer Rat Thyroid cells, transfected with α,β,γ-mENaC had a significantly greater membrane capacitance response to cAMP stimulation compared to non-ENaC controls. Finally, immunofluorescent labeling and quantitation revealed a smaller number of vesicles in cells where ENaC expression was reduced. These findings indicate that ENaC is not a passive passenger in regulated epithelial vesicle trafficking, but plays a role in establishing and maintaining the pool of vesicles that respond to cAMP stimulation.
authors.affiliation: Department of Medicine, Renal-Electrolyte Division, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Edinger
authors.forename: Carol A
authors.initials: CA
authors.lastname: Bertrand
authors.forename: Christine
authors.initials: C
authors.lastname: Rondandino
authors.forename: Gerard A
authors.initials: GA
authors.lastname: Apodaca
authors.forename: John P
authors.initials: JP
authors.lastname: Johnson
authors.forename: Michael B
authors.initials: MB
authors.lastname: Butterworth
mesh_terms: D000450:Aldosterone / Q000502:physiology; D000818:Animals; D016764:Cell Polarity; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D003470:Culture Media; D000242:Cyclic AMP / Q000502:physiology; D022162:Cytoplasmic Vesicles / Q000378:metabolism*; D025802:Electric Capacitance; D004847:Epithelial Cells / Q000378:metabolism / Q000502:physiology; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D051379:Mice; D021381:Protein Transport; D034622:RNA Interference; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D003470:Culture Media; D053503:Epithelial Sodium Channels; D005576:Colforsin; D000450:Aldosterone; D000242:Cyclic AMP