title: A single nucleotide polymorphism alters the activity of the renal Na+:Cl- cotransporter and reveals a role for transmembrane segment 4 in chloride and thiazide affinity.
abstract: The thiazide-sensitive Na+:Cl- cotransporter is the major salt transport pathway in the distal convoluted tubule of the kidney, and a role of this cotransporter in blood pressure homeostasis has been defined by physiological studies on pressure natriuresis and by its involvement in monogenic diseases that feature arterial hypotension or hypertension. Data base analysis revealed that 135 single nucleotide polymorphisms along the human SLC12A3 gene that encodes the Na+:Cl- cotransporter have been reported. Eight are located within the coding region, and one results in a single amino acid change; the residue glycine at the position 264 is changed to alanine (G264A). This residue is located within the fourth transmembrane domain of the predicted structure. Because Gly-264 is a highly conserved residue, we studied the functional properties of this polymorphism by using in vitro mutagenesis and the heterologous expression system in Xenopus laevis oocytes. G264A resulted in a significant and reproducible reduction ( approximately 50%) in (22)Na+ uptake when compared with the wild type cotransporter. The affinity for extracellular Cl- and for thiazide diuretics was increased in G264A. Western blot analysis showed similar immunoreactive bands between the wild type and the G264A cotransporters, and confocal images of oocytes injected with enhanced green fluorescent protein-tagged wild type and G264A cotransporter showed no differences in the protein surface expression level. These observations suggest that the G264A polymorphism is associated with reduction in the substrate translocation rate of the cotransporter, due to a decrease in the intrinsic activity. Our study also reveals a role of the transmembrane segment 4 in defining the affinity for extracellular Cl- and thiazide diuretics.
authors.affiliation: Molecular Physiology Unit, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México and Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan 14000, Mexico City, Mexico.
authors.forename: Erika
authors.initials: E
authors.lastname: Moreno
authors.forename: Claudia
authors.initials: C
authors.lastname: Tovar-Palacio
authors.forename: Paola
authors.initials: P
authors.lastname: de los Heros
authors.forename: Blanca
authors.initials: B
authors.lastname: Guzmán
authors.forename: Norma A
authors.initials: NA
authors.lastname: Bobadilla
authors.forename: Norma
authors.initials: N
authors.lastname: Vázquez
authors.forename: Daniela
authors.initials: D
authors.lastname: Riccardi
authors.forename: Esteban
authors.initials: E
authors.lastname: Poch
authors.forename: Gerardo
authors.initials: G
authors.lastname: Gamba
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D001581:Benzothiadiazines; D001665:Binding Sites / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D004232:Diuretics; D005260:Female; D006801:Humans; D017136:Ion Transport; D007668:Kidney / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D020641:Polymorphism, Single Nucleotide; D051381:Rats; D011955:Receptors, Drug / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D049993:Sodium Chloride Symporter Inhibitors / Q000378:metabolism; D049992:Sodium Chloride Symporters; D064486:Solute Carrier Family 12, Member 3; D013329:Structure-Activity Relationship; D027981:Symporters
chemical_list: D001581:Benzothiadiazines; D002352:Carrier Proteins; D002712:Chlorides; D004232:Diuretics; D011955:Receptors, Drug; C578874:SLC12A3 protein, human; C578876:Slc12a3 protein, rat; D049993:Sodium Chloride Symporter Inhibitors; D049992:Sodium Chloride Symporters; D064486:Solute Carrier Family 12, Member 3; D027981:Symporters; C064415:thiazide receptor