title: Intersubunit conformational changes mediate epithelial sodium channel gating.
abstract: The epithelial Na(+) channel (ENaC) functions as a pathway for Na(+) absorption in the kidney and lung, where it is crucial for Na(+) homeostasis and blood pressure regulation. However, the basic mechanisms that control ENaC gating are poorly understood. Here we define a role in gating for residues forming interfaces between the extracellular domains of the three ENaC subunits. Using cysteine substitution combined with chemical cross-linking, we determined that residues located at equivalent positions in the three subunits (αK477, βE446, and γE455) form interfaces with residues in adjacent subunits (βV85, γV87, and αL120, respectively). Cross-linking of these residues altered ENaC activity in a length-dependent manner; long cross-linkers increased ENaC current by increasing its open probability, whereas short cross-linkers reduced ENaC open probability. Cross-linking also disrupted ENaC gating responses to extracellular pH and Na(+), signals which modulate ENaC activity during shifts in volume status. Introduction of charged side chains at the interfacing residues altered ENaC activity in a charge-dependent manner. Current increased when like charges were present at both interfacing residues, whereas opposing charges reduced current. Together, these data indicate that conformational changes at intersubunit interfaces participate in ENaC transitions between the open and closed states; movements that increase intersubunit distance favor the open state, whereas the closed state is favored when the distance is reduced. This provides a mechanism to modulate ENaC gating in response to changing extracellular conditions that threaten Na(+) homeostasis.
authors.affiliation: Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Collier
authors.affiliation: Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242.
authors.forename: Vivian R
authors.initials: VR
authors.lastname: Tomkovicz
authors.affiliation: Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242.
authors.forename: Zerubbabel J
authors.initials: ZJ
authors.lastname: Peterson
authors.affiliation: Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Iowa City VA Health Care System, Iowa City, IA 52246.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Benson
authors.affiliation: Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Iowa City VA Health Care System, Iowa City, IA 52246 peter-snyder@uiowa.edu.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Snyder
mesh_terms: D000818:Animals; D003432:Cross-Linking Reagents; D004247:DNA / Q000737:chemistry; D053503:Epithelial Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008958:Models, Molecular; D008968:Molecular Conformation; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D003432:Cross-Linking Reagents; D053503:Epithelial Sodium Channels; D004247:DNA; D012964:Sodium