Extracellular histidine residues crucial for Na+ self-inhibition of epithelial Na+ channels.
Epithelial Na(+) channels (ENaC) participate in the regulation of extracellular fluid volume homeostasis and blood pressure. Channel activity is regulated by both extracellular and intracellular Na(+). The down-regulation of ENaC activity by external Na(+) is referred to as Na(+) self-inhibition. We investigated the structural determinants of Na(+) self-inhibition by expressing wild-type or mutant ENaCs in Xenopus oocytes and analyzing changes in whole-cell Na(+) currents following a rapid increase of bath Na(+) concentration. Our results indicated that wild-type mouse alphabetagammaENaC has intrinsic Na(+) self-inhibition similar to that reported for human, rat, and Xenopus ENaCs. Mutations at His(239) (gammaH239R, gammaH239D, and gammaH239C) in the extracellular loop of the gammaENaC subunit prevented Na(+) self-inhibition whereas mutations of the corresponding His(282) in alphaENaC (alphaH282D, alphaH282R, alphaH282W, and alphaH282C) significantly enhanced Na(+) self-inhibition. These results suggest that these two histidine residues within the extracellular loops are crucial structural determinants for Na(+) self-inhibition.
Sheng
Shaohu
S
Renal-Electrolyte Division, Department of Medicine, School of Medicine, University of Pittsburgh, Pennsylvania 15261, USA. shaohu@pitt.edu
Bruns
James B
JB
Kleyman
Thomas R
TR
D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005799:Genes, Dominant; D006639:Histidine / Q000737:chemistry*; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000737:chemistry / Q000378:metabolism*; D015222:Sodium Channels / Q000737:chemistry*; D013997:Time Factors; D014981:Xenopus
D018076:DNA, Complementary; D015222:Sodium Channels; D006639:Histidine; D012964:Sodium