title: Cloning and expression of the epithelial sodium channel and its role in osmoregulation of aquatic and estivating African lungfish Protopterus annectens.
abstract: The epithelial sodium channel (ENaC) is a sodium (Na(+))-selective aldosterone-stimulated ion channel involved in Na(+) transport homeostasis of tetrapods. We examined full-length cDNA sequences and tissue distributions of ENaCα, ENaCβ, and ENaCγ subunits in the African lungfish Protopterus annectens. Protopterus ENaC (pENaC) comprises 3 subunits: pENaCα, pENaCβ, and pENaCγ. pENaCα, pENaCβ, and pENaCγ subunits are closely related to α, β, and γ subunits of the Australian lungfish Neoceratodus forsteri ENaC (nENaC), respectively. Three ENaC subunit mRNAs were highly expressed in the gills and moderately expressed in the kidney and rectum of P. annectens. During estivation for 2-4weeks and 2-3months, plasma Na(+) concentration was relatively stable, but plasma urea concentration significantly increased in comparison with the control fish kept in a freshwater environment. Plasma aldosterone concentration and mRNA expression of the ENaCα subunit gradually and significantly decreased in the gills and kidney after 2months of estivation. Thus, aldosterone-dependent Na(+) absorption via ENaC probably exists in the epithelial cells of osmoregulatory organs of lungfish kept in fresh water, whereas plasma Na(+) concentration may be maintained by a mechanism independent of aldosterone-ENaC axis during estivation in lungfish.
authors.affiliation: Department of Life and Environmental Science, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan. Electronic address: uchiyama@sci.u-toyama.ac.jp.
authors.forename: Minoru
authors.initials: M
authors.lastname: Uchiyama
authors.affiliation: Department of Life and Environmental Science, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
authors.forename: Norifumi
authors.initials: N
authors.lastname: Konno
authors.affiliation: Department of Life and Environmental Science, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
authors.forename: Sachika
authors.initials: S
authors.lastname: Shibuya
authors.affiliation: Department of Life and Environmental Science, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nogami
mesh_terms: D000450:Aldosterone / Q000097:blood; D000595:Amino Acid Sequence; D000818:Animals; D001835:Body Weight; D003001:Cloning, Molecular; D018076:DNA, Complementary; D055864:Droughts; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D005399:Fishes / Q000502:physiology*; D005618:Fresh Water; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D064587:Osmoregulation; D010802:Phylogeny; D021122:Protein Subunits; D012964:Sodium / Q000097:blood
chemical_list: D018076:DNA, Complementary; D053503:Epithelial Sodium Channels; D029941:Fish Proteins; D021122:Protein Subunits; D000450:Aldosterone; D012964:Sodium
keywords: Aldosterone; Dipnoi; Estivation; Plasma sodium concentration; Plasma urea concentration; Sodium channel