Transport of Water and Glycerol in Aquaporin 3 Is Gated by H

• Published in: The Journal of biological chemistry 1999-07, Vol.274 (31), p.21631-21636
• Main Authors: Zeuthen, Thomas, Klaerke, Dan Arne
• Format: Article
• Language: English
• Subjects: Alcohols - metabolism; Animals; Aquaporin 3; Aquaporins - genetics; Aquaporins - metabolism; Cell Membrane - physiology; Cell Membrane Permeability; Glycerol - metabolism; Hydrogen-Ion Concentration; Kinetics; Oocytes - physiology; Recombinant Proteins - metabolism; RNA, Messenger - genetics; Structure-Activity Relationship; Water - metabolism; Xenopus laevis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.274.31.21631

Aquaporins (AQPs) were expressed in Xenopus laevis oocytes in order to study the effects of external pH and solute structure on permeabilities. For AQP3 the osmotic water permeability, Lp, was abolished at acid pH values with a pK of 6.4 and a Hill coefficient of 3. TheLp values of AQP0, AQP1, AQP2, AQP4, and AQP5 were independent of pH. For AQP3 the glycerol permeabilityPGl, obtained from [14C]glycerol uptake, was abolished at acid pH values with a pK of 6.1 and a Hill coefficient of 6. Consequently, AQP3 acts as a glycerol and water channel at physiological pH, but predominantly as a glycerol channel at pH values around 6.1. The pH effects were reversible. The interactions between fluxes of water and straight chain polyols were inferred from reflection coefficients (ς). For AQP3, water and glycerol interacted by competing for titratable site(s): ςGl was 0.15 at neutral pH but doubled at pH 6.4. The ς values were smaller for polyols in which the —OH groups were free to form hydrogen bonds. The activation energy for the transport processes was around 5 kcal mol−1. We suggest that water and polyols permeate AQP3 by forming successive hydrogen bonds with titratable sites.