A new subunit of the epithelial Na+ channel identifies regions involved in Na+ self-inhibition.
The epithelial Na+ channel (ENaC) is the apical entry pathway for Na+ in many Na+-reabsorbing epithelia. ENaC is a heterotetrameric protein composed of homologous alpha, beta, and gamma subunits. Mutations in ENaC cause severe hypertension or salt wasting in humans; and consequently, ENaC activity is tightly controlled. According to the concept of Na+ self-inhibition, the extracellular Na+ ion itself can reduce ENaC activity. The molecular basis for Na+ self-inhibition is unknown. Here, we describe cloning of a new ENaC subunit from Xenopus laevis (epsilonxENaC). epsilonxENaC can replace alphaxENaC and formed functional, highly selective, amiloride-sensitive Na+ channels when coexpressed with betaxENaC and gammaxENaC. Channels containing epsilonxENaC showed strong inhibition by extracellular Na+. This Na+ self-inhibition was significantly slower than for alphaxENaC-containing channels. Using site-directed mutagenesis, we show that the proximal part of the large extracellular domain controls the speed of self-inhibition. This suggests that this region is involved in conformational changes during Na+ self-inhibition.
Babini
Elena
E
Departments of Physiology II and Otolaryngology, Research Group of Sensory Physiology, University of Tübingen, D-72076 Tübingen, Germany.
Geisler
Hyun-Soon
HS
Siba
Maria
M
Gründer
Stefan
S
D000584:Amiloride / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003001:Cloning, Molecular; D004553:Electric Conductivity; D053503:Epithelial Sodium Channels; D005260:Female; D015870:Gene Expression; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D016415:Sequence Alignment; D012964:Sodium / Q000494:pharmacology*; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D013329:Structure-Activity Relationship; D014162:Transfection; D014982:Xenopus laevis
D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D000584:Amiloride; D012964:Sodium