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Rapid gating and anion permeability of an intracellular aquaporin

Nature volume 402, pages 184–187 (1999)Cite this article

Abstract

Aquaporin (AQP) water-channel proteins are freely permeated by water but not by ions or charged solutes1. Although mammalian aquaporins were believed to be located in plasma membranes, rat AQP6 is restricted to intracellular vesicles in renal epithelia2. Here we show that AQP6 is functionally distinct from other known aquaporins. When expressed in Xenopus laevis oocytes, AQP6 exhibits low basal water permeability; however, when treated with the known water channel inhibitor, Hg2+, the water permeability of AQP6 oocytes rapidly rises up to tenfold and is accompanied by ion conductance. AQP6 colocalizes with H+-ATPase in intracellular vesicles of acid-secreting α-intercalated cells in renal collecting duct. At pH less than 5.5, anion conductance is rapidly and reversibly activated in AQP6 oocytes. Site-directed mutation of lysine to glutamate at position 72 in the cytoplasmic mouth of the pore changes the cation/anion selectivity, but leaves low pH activation intact. Our results demonstrate unusual biophysical properties of an aquaporin, and indicate that anion-channel function may now be explored in a protein with known structure.

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Figure 1: Water permeability of AQP6.
Figure 2: Electrophysiological analysis of AQP6.
Figure 3: Immunogold electron microscopic colocalization of AQP6 (5-nm particles, arrowheads) and H+-ATPase (10-nm particles, arrows) in intracellular vesicles of α-intercalated cells of rat renal collecting duct.
Figure 4: Effect of pH on water permeability and ion conductance of AQP6.
Figure 5: Electrophysiology of wild-type AQP6 and the K72E mutant.

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Acknowledgements

We thank M. Lu for the AQP6 plasmid, M. A. Knepper for the anti-H+-ATPase, and M. R. T. Hall for confocal microscopy. Support was provided by grants from the NIH and the Cystic Fibrosis Foundation (P.A. and W.B.G.), the Human Frontier Science Program (M.Y.), and the Novo Nordic Foundation, the Karen Elise Jensen Foundation, the Danish Medical Research Council, the Biomembrane Research Center at Unviersity of Aarhus and the EU Commission (EU-Biotech and TMR Programmes) (S.N.).

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  1. Masato Yasui, Akihiro Hazama, Tae-Hwan Kwon and Søren Nielsen: These authors contributed equally to this work

Authors and Affiliations

  1. Departments of Biological Chemistry, Medicine, Johns Hopkins University School of Medicine, MD 21205, Baltimore, USA

    Masato Yasui & Peter Agre

  2. Physiology, Johns Hopkins University School of Medicine, MD 21205, Baltimore, USA

    Akihiro Hazama & Wm. B. Guggino

  3. Department of Cell Biology, Institute of Anatomy, University of Aarhus, DK-8000, Denmark

    Tae-Hwan Kwon & Søren Nielsen

Authors
  1. Masato Yasui
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  2. Akihiro Hazama
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  4. Søren Nielsen
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  5. Wm. B. Guggino
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  6. Peter Agre
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Correspondence to Peter Agre.

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Yasui, M., Hazama, A., Kwon, TH. et al. Rapid gating and anion permeability of an intracellular aquaporin. Nature 402, 184–187 (1999). https://doi.org/10.1038/46045

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