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XB-ART-39330
Proc Natl Acad Sci U S A 2009 Mar 31;10613:5406-11. doi: 10.1073/pnas.0813231106.
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Relative CO2/NH3 selectivities of AQP1, AQP4, AQP5, AmtB, and RhAG.

Musa-Aziz R , Chen LM , Pelletier MF , Boron WF .


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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.

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Species referenced: Xenopus
Genes referenced: aqp1 aqp4 aqp5 gnas mapt rhag slc12a1 slc15a1 slc5a1 slc5a1.2

References [+] :
Andrade, Crystal structure of the archaeal ammonium transporter Amt-1 from Archaeoglobus fulgidus. 2005, Pubmed