The epithelial sodium channel in the Australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi).
Epithelial sodium channel (ENaC) is a Na(+)-selective, aldosterone-stimulated ion channel involved in sodium transport homeostasis. ENaC is rate-limiting for Na(+) absorption in the epithelia of osmoregulatory organs of tetrapods. Although the ENaC/degenerin gene family is proposed to be present in metazoans, no orthologues or paralogues for ENaC have been found in the genome databases of teleosts. We studied full-length cDNA cloning and tissue distributions of ENaCα, β and γ subunits in the Australian lungfish, Neoceratodus forsteri, which is the closest living relative of tetrapods. Neoceratodus ENaC (nENaC) comprised three subunits: nENaCα, β and γ proteins. The nENaCα, β and γ subunits are closely related to amphibian ENaCα, β and γ subunits, respectively. Three ENaC subunit mRNAs were highly expressed in the gills, kidney and rectum. Amiloride-sensitive sodium current was recorded from Xenopus oocytes injected with the nENaCαβγ subunit complementary RNAs under a two-electrode voltage clamp. nENaCα immunoreactivity was observed in the apical cell membrane of the gills, kidney and rectum. Thus, nENaC may play a role in regulating sodium transport of the lungfish, which has a renin-angiotensin-aldosterone system. This is interesting because there may have been an ENaC sodium absorption system controlled by aldosterone before the conquest of land by vertebrates.
Department of Life and Environmental Science, Graduate School of Science and Engineering, University of Toyama, , 3190 Gofuku, Toyama 930-8555, Japan. uchiyama@sci.u-toyama.ac.jp
Minoru
M
Uchiyama
Sho
S
Maejima
Sumio
S
Yoshie
Yoshihiro
Y
Kubo
Norifumi
N
Konno
Jean M P
JM
Joss
D000595:Amino Acid Sequence; D000818:Animals; D001315:Australia; D003001:Cloning, Molecular; D055724:Electrophysiological Phenomena; D053503:Epithelial Sodium Channels / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D005399:Fishes / Q000502:physiology*; D005786:Gene Expression Regulation; D005880:Gills / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D010802:Phylogeny; D021122:Protein Subunits; D012007:Rectum / Q000378:metabolism; D012084:Renin-Angiotensin System / Q000502:physiology; D014981:Xenopus
D053503:Epithelial Sodium Channels; D021122:Protein Subunits