Relative CO2/NH3 selectivities of AQP1, AQP4, AQP5, AmtB, and RhAG.
The water channel aquaporin 1 (AQP1) and certain Rh-family members are permeable to CO(2) and NH(3). Here, we use changes in surface pH (pH(S)) to assess relative CO(2) vs. NH(3) permeability of Xenopus oocytes expressing members of the AQP or Rh family. Exposed to CO(2) or NH(3), AQP1 oocytes exhibit a greater maximal magnitude of pH(S) change (DeltapH(S)) compared with day-matched controls injected with H(2)O or with RNA encoding SGLT1, NKCC2, or PepT1. With CO(2), AQP1 oocytes also have faster time constants for pH(S) relaxation (tau(pHs)). Thus, AQP1, but not the other proteins, conduct CO(2) and NH(3). Oocytes expressing rat AQP4, rat AQP5, human RhAG, or the bacterial Rh homolog AmtB also exhibit greater DeltapH(S)(CO(2)) and faster tau(pHs) compared with controls. Oocytes expressing AmtB and RhAG, but not AQP4 or AQP5, exhibit greater DeltapH(S)(NH(3)) values. Only AQPs exhibited significant osmotic water permeability (P(f)). We computed channel-dependent (*) DeltapH(S) or P(f) by subtracting values for H(2)O oocytes from those of channel-expressing oocytes. For the ratio DeltapH(S)(CO(2))*/P(f)*, the sequence was AQP5 > AQP1 congruent with AQP4. For DeltapH(S)(CO(2))*/DeltapH(S)(NH(3))*, the sequence was AQP4 congruent with AQP5 > AQP1 > AmtB > RhAG. Thus, each channel exhibits a characteristic ratio for indices of CO(2) vs. NH(3) permeability, demonstrating that, like ion channels, gas channels can exhibit selectivity.
Musa-Aziz
Raif
R
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA. raif.aziz@case.edu
Chen
Li-Ming
LM
Pelletier
Marc F
MF
Boron
Walter F
WF
D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D051398:Aquaporin 1; D051401:Aquaporin 4; D051402:Aquaporin 5; D020346:Aquaporins / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000378:metabolism*; D002463:Cell Membrane Permeability; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009865:Oocytes; D030781:Organisms, Genetically Modified; D051381:Rats; D014162:Transfection; D014981:Xenopus
C111096:AmtB protein, E coli; C496032:Aqp4 protein, rat; C496040:Aqp5 protein, rat; D051401:Aquaporin 4; D051402:Aquaporin 5; D020346:Aquaporins; D001798:Blood Proteins; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D008562:Membrane Glycoproteins; C498523:RHAG protein, human; D002245:Carbon Dioxide; D051398:Aquaporin 1; D000641:Ammonia