Relative CO₂/NH₃ selectivities of AQP1, AQP4, AQP5, AmtB, and RhAG

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 13; pp. 5406 - 5411
• Main Authors: Musa-Aziz, Raif, Chen, Li-Ming, Pelletier, Marc F, Boron, Walter F
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 31.03.2009; National Acad Sciences
• Subjects: Ammonia; Ammonia - metabolism; Animals; Aquaporin 1; Aquaporin 4; Aquaporin 5; Aquaporins; Aquaporins - metabolism; Biological Sciences; Blood Proteins - metabolism; Carbon Dioxide - metabolism; Cation Transport Proteins - metabolism; Cell Membrane Permeability; Cell membranes; Complementary DNA; Complementary RNA; Electrodes; Escherichia coli Proteins - metabolism; Humans; Hydrogen-Ion Concentration; Membrane Glycoproteins - metabolism; Oocytes; Organisms, Genetically Modified; Quaternary ammonium compounds; Rats; Transfection; Water channels; Xenopus
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0813231106

The water channel aquaporin 1 (AQP1) and certain Rh-family members are permeable to CO₂ and NH₃. Here, we use changes in surface pH (pHS) to assess relative CO₂ vs. NH₃ permeability of Xenopus oocytes expressing members of the AQP or Rh family. Exposed to CO₂ or NH₃, AQP1 oocytes exhibit a greater maximal magnitude of pHS change (ΔpHS) compared with day-matched controls injected with H₂O or with RNA encoding SGLT1, NKCC2, or PepT1. With CO₂, AQP1 oocytes also have faster time constants for pHS relaxation (τpHs). Thus, AQP1, but not the other proteins, conduct CO₂ and NH₃. Oocytes expressing rat AQP4, rat AQP5, human RhAG, or the bacterial Rh homolog AmtB also exhibit greater ΔpHS(CO₂) and faster τpHs compared with controls. Oocytes expressing AmtB and RhAG, but not AQP4 or AQP5, exhibit greater ΔpHS(NH₃) values. Only AQPs exhibited significant osmotic water permeability (Pf). We computed channel-dependent (*) ΔpHS or Pf by subtracting values for H₂O oocytes from those of channel-expressing oocytes. For the ratio ΔpHS(CO₂)*/P[Formula: see text]*, the sequence was AQP5 > AQP1 [congruent with] AQP4. For ΔpHS(CO₂)*/ΔpHS(NH₃)*, the sequence was AQP4 [congruent with] AQP5 > AQP1 > AmtB > RhAG. Thus, each channel exhibits a characteristic ratio for indices of CO₂ vs. NH₃ permeability, demonstrating that, like ion channels, gas channels can exhibit selectivity.