title: Intracellular Cl- as a signaling ion that potently regulates Na+/HCO3- transporters.
abstract: Cl(-) is a major anion in mammalian cells involved in transport processes that determines the intracellular activity of many ions and plasma membrane potential. Surprisingly, a role of intracellular Cl(-) (Cl(-) in) as a signaling ion has not been previously evaluated. Here we report that Cl(-) in functions as a regulator of cellular Na(+) and HCO3 (-) concentrations and transepithelial transport through modulating the activity of several electrogenic Na(+)-HCO3 (-) transporters. We describe the molecular mechanism(s) of this regulation by physiological Cl(-) in concentrations highlighting the role of GXXXP motifs in Cl(-) sensing. Regulation of the ubiquitous Na(+)-HCO3(-) co-transport (NBC)e1-B is mediated by two GXXXP-containing sites; regulation of NBCe2-C is dependent on a single GXXXP motif; and regulation of NBCe1-A depends on a cryptic GXXXP motif. In the basal state NBCe1-B is inhibited by high Cl(-) in interacting at a low affinity GXXXP-containing site. IP3 receptor binding protein released with IP3 (IRBIT) activation of NBCe1-B unmasks a second high affinity Cl(-) in interacting GXXXP-dependent site. By contrast, NBCe2-C, which does not interact with IRBIT, has a single high affinity N-terminal GXXP-containing Cl(-) in interacting site. NBCe1-A is unaffected by Cl(-) in between 5 and 140 mM. However, deletion of NBCe1-A residues 29-41 unmasks a cryptic GXXXP-containing site homologous with the NBCe1-B low affinity site that is involved in inhibition of NBCe1-A by Cl(-) in. These findings reveal a cellular Cl(-) in sensing mechanism that plays an important role in the regulation of Na(+) and HCO3 (-) transport, with critical implications for the role of Cl(-) in cellular ion homeostasis and epithelial fluid and electrolyte secretion.
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, MD 20892;
authors.forename: Nikolay
authors.initials: N
authors.lastname: Shcheynikov
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, MD 20892;
authors.forename: Aran
authors.initials: A
authors.lastname: Son
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, MD 20892; Department of Physiology, Graduate School of Medicine, Gachon University, Yeonsu-gu, Incheon, 406-799, South Korea;
authors.forename: Jeong Hee
authors.initials: JH
authors.lastname: Hong
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, MD 20892;
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamazaki
authors.affiliation: Department of Clinical Biochemistry and Pharmacology, the Faculty of Health Sciences, Ben Gurion University of the Negev, 8410501 Bear Sheva, Israel;
authors.forename: Ehud
authors.initials: E
authors.lastname: Ohana
authors.affiliation: Division of Nephrology, Department of Medicine, and Brain Research Institute, University of California, Los Angeles, CA 90095; and.
authors.forename: Ira
authors.initials: I
authors.lastname: Kurtz
authors.affiliation: Department of Oral Biology, BK 21 PLUS Project, Yonsei University College of Dentistry, Seoul 120-752, Korea dmshin@yuhs.ac Shmuel.Muallem@nih.gov.
authors.forename: Dong Min
authors.initials: DM
authors.lastname: Shin
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, MD 20892; dmshin@yuhs.ac Shmuel.Muallem@nih.gov.
authors.forename: Shmuel
authors.initials: S
authors.lastname: Muallem
mesh_terms: D000595:Amino Acid Sequence; D002712:Chlorides / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D015398:Signal Transduction; D027982:Sodium-Bicarbonate Symporters / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002712:Chlorides; D027982:Sodium-Bicarbonate Symporters
keywords: intracellular Cl−; signaling ion; transporters