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Relative CO 2 /NH 3 permeabilities of human RhAG, RhBG, and RhCG
Author(s) -
Geyer R.Ryan,
Parker Mark D.,
Burton Nick,
Boron Walter F.,
Toye Ashley M.,
MusaAziz Raif
Publication year - 2011
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.25.1_supplement.1040.4
Subject(s) - chemistry , mutant , xenopus , biophysics , biochemistry , biology , gene
Mammalian Rhesus (Rh) proteins include the erythroid RhAG, RhCE, RhD, and non‐erythroid RhBG and RhCG. In rodents, both RhBG and RhCG are present in kidney and liver, but only RhCG is detectable in these organs in humans. Here we expressed human RhAG, RhBG, and RhCG in Xenopus oocytes ( vs H 2 O‐injected control oocytes) and used microelectrodes to monitor the maximum transient change in surface pH (ΔpH S ) caused by exposing the same oocyte to 5% CO 2 /33 mM HCO 3 (an increase) or 0.5 mM NH 3 /NH 4 + (a decrease). Subtracting the respective values for day‐matched, H 2 O‐injected control oocytes yielded channel‐specific values (*). (ΔpH S *) CO2 and (ΔpH S *) NH3 were each significantly greater than 0 for all channels, indicating that RhAG, RhBG and RhCG each can carry CO 2 and NH 3 . As a control, we mutated a conserved residue known to be important for NH 3 permeability and/or channel trafficking of RhAG (D167). The two mutants—D178N‐RhBG and D177N‐RhCG—did not significantly conduct either CO 2 or NH 3 . Thus, we confirm that RhAG, RhBG and RhCG all have significant NH 3 permeability, that RhAG has significant CO 2 permeability, and we demonstrate for the first time that RhBG and RhCG have significant CO 2 permeability. (ΔpH S *) CO2 /(−ΔpH S *) NH3 fell in the sequence: RhBG (0.66±0.17, N=11) > RhCG (0.44±0.09, N=13) > RhAG (0.32±0.06, N=10), representing a 2‐fold range of CO 2 /NH 3 permeability ratios.