title: The pH sensitivity of Aqp0 channels in tetraploid and diploid teleosts.
abstract: Water homeostasis and the structural integrity of the vertebrate lens is partially mediated by AQP0 channels. Emerging evidence indicates that external pH may be involved in channel gating. Here we show that a tetraploid teleost, the Atlantic salmon, retains 4 aqp0 genes (aqp0a1, -0a2, -0b1, and -0b2), which are highly, but not exclusively, expressed in the lens. Functional characterization reveals that, although each paralog permeates water efficiently, the permeability is respectively shifted to the neutral, alkaline, or acidic pH in Aqp0a1, -0a2, and -0b1, whereas that of Aqp0b2 is not regulated by external pH. Mutagenesis studies demonstrate that Ser(38), His(39), and His(40) residues in the extracellular transmembrane domain of α-helix 2 facing the water pore are critical for the pH modulation of water transport. To validate these findings, we show that both zebrafish Aqp0a and -0b are functional water channels with respective pH sensitivities toward alkaline or acid pH ranges and that an N-terminal allelic variant (Ser(19)) of Aqp0b exists that abolishes water transport in Xenopus laevis oocytes. The data suggest that the alkaline pH sensitivity is a conserved trait in teleost Aqp0 a-type channels, whereas mammalian AQP0 and some teleost Aqp0 b-type channels display an acidic pH permeation preference.
authors: *Department of Biology, Bergen High Technology Centre, University of Bergen, Bergen, Norway; Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain; and Institute of Marine Research, Nordnes, Bergen, Norway.
authors: François
authors: F
authors: Chauvigné
authors: *Department of Biology, Bergen High Technology Centre, University of Bergen, Bergen, Norway; Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain; and Institute of Marine Research, Nordnes, Bergen, Norway.
authors: Cinta
authors: C
authors: Zapater
authors: *Department of Biology, Bergen High Technology Centre, University of Bergen, Bergen, Norway; Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain; and Institute of Marine Research, Nordnes, Bergen, Norway.
authors: Jon Anders
authors: JA
authors: Stavang
authors: *Department of Biology, Bergen High Technology Centre, University of Bergen, Bergen, Norway; Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain; and Institute of Marine Research, Nordnes, Bergen, Norway.
authors: Geir Lasse
authors: GL
authors: Taranger
authors: *Department of Biology, Bergen High Technology Centre, University of Bergen, Bergen, Norway; Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain; and Institute of Marine Research, Nordnes, Bergen, Norway nigel.finn@bio.uib.no joan.cerda@irta.cat.
authors: Joan
authors: J
authors: Cerdà
authors: *Department of Biology, Bergen High Technology Centre, University of Bergen, Bergen, Norway; Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain; and Institute of Marine Research, Nordnes, Bergen, Norway nigel.finn@bio.uib.no joan.cerda@irta.cat.
authors: Roderick Nigel
authors: RN
authors: Finn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002463:Cell Membrane Permeability / Q000502:physiology*; D002478:Cells, Cultured; D004171:Diploidy; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005399:Fishes; D006863:Hydrogen-Ion Concentration; D007908:Lens, Crystalline / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D010802:Phylogeny; D011487:Protein Conformation; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D057891:Tetraploidy; D014867:Water / Q000378:metabolism*; D014982:Xenopus laevis; D015027:Zebrafish
chemical_list: D020346:Aquaporins; D005136:Eye Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C030328:aquaporin 0; D014867:Water
keywords: aquaporin; cataract; permeability lens; water transport