title: Selectivity of the renal collecting duct water channel aquaporin-3.
abstract: Aquaporin-3 (AQP3) is a water channel found in the basolateral cell membrane of principal cells of the renal collecting tubule as well as in other epithelia. To examine the selectivity of AQP3, the permeability to water (Pf), urea (Pur), and glycerol (Pgly) of Xenopus oocytes injected with cRNA encoding AQP3 was measured. Oocytes injected with cRNA encoding either human or rat aquaporin-1 (AQP1) were used as controls. Although both aquaporins permit water flow across the cell membrane, only AQP3 was permeable to glycerol and urea (Pgly > Pur). The uptake of glycerol into oocytes expressing AQP3 was linear up to 165 mM. For AQP3 the Arrhenius energy of activation for Pf was 3 kcal/mol, whereas for Pgly and Pur it was >12 kcal/mol. The sulfhydryl reagent p-chloromercuriphenylsulfonate (1 mM) abolished Pf of AQP3, whereas it did not affect Pgly. In addition, phloretin (0.1 mM) inhibited Pf of AQP3 by 35%, whereas it did not alter Pgly or Pur. We conclude that water does not share the same pathway with glycerol or urea in AQP3 and that this aquaporin, therefore, forms a water-selective channel.
authors.affiliation: Department of Physiology and Biophysics, Cornell University Medical College, New York, New York 10021, USA.
authors.forename: M
authors.initials: M
authors.lastname: Echevarría
authors.forename: E E
authors.initials: EE
authors.lastname: Windhager
authors.forename: G
authors.initials: G
authors.lastname: Frindt
mesh_terms: D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D051398:Aquaporin 1; D051400:Aquaporin 3; D020346:Aquaporins; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry; D001692:Biological Transport; D001789:Blood Group Antigens; D002151:Calorimetry; D002463:Cell Membrane Permeability; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins; D005260:Female; D005990:Glycerol / Q000378:metabolism; D006801:Humans; D007473:Ion Channels / Q000096:biosynthesis / Q000737:chemistry / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000502:physiology*; D007700:Kinetics; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D010693:Phloretin / Q000494:pharmacology; D018075:RNA, Complementary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics; D014508:Urea / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: C496020:AQP1 protein, human; C496027:AQP3 protein, human; C496022:Aqp1 protein, rat; C496029:Aqp3 protein, rat; D020346:Aquaporins; D001425:Bacterial Outer Membrane Proteins; D001789:Blood Group Antigens; D029968:Escherichia coli Proteins; D007473:Ion Channels; D018075:RNA, Complementary; C078043:GlpF protein, E coli; D051398:Aquaporin 1; D051400:Aquaporin 3; D002731:4-Chloromercuribenzenesulfonate; D014508:Urea; D005990:Glycerol; D010693:Phloretin