Rapid gating and anion permeability of an intracellular aquaporin

Masato Yasui, Akihiro Hazama, Tae-Hwan Kwon, Søren Nielsen, Wm. B. Guggino and Peter Agre ()
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Masato Yasui: Johns Hopkins University School of Medicine
Akihiro Hazama: Johns Hopkins University School of Medicine
Tae-Hwan Kwon: Institute of Anatomy, University of Aarhus
Søren Nielsen: Institute of Anatomy, University of Aarhus
Wm. B. Guggino: Johns Hopkins University School of Medicine
Peter Agre: Johns Hopkins University School of Medicine

Nature, 1999, vol. 402, issue 6758, 184-187

Abstract: 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.

Date: 1999
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DOI: 10.1038/46045

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