期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2009
卷号：106
期号：13
页码：5406-5411
DOI：10.1073/pnas.0813231106
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：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 ({Delta}pHS) 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 ({tau}pHs). 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 {Delta}pHS(CO2) and faster {tau}pHs compared with controls. Oocytes expressing AmtB and RhAG, but not AQP4 or AQP5, exhibit greater {Delta}pHS(NH3) values. Only AQPs exhibited significant osmotic water permeability (Pf). We computed channel-dependent (*) {Delta}pHS or Pf by subtracting values for H2O oocytes from those of channel-expressing oocytes. For the ratio {Delta}pHS(CO2)*/P[IMG]f1.gif" ALT="Formula" BORDER="0">*, the sequence was AQP5 > AQP1 {cong} AQP4. For {Delta}pHS(CO2)*/{Delta}pHS(NH3)*, the sequence was AQP4 {cong} 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.
