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The role of carbonic anhydrase II on HCO 3 − ‐initiated transport through the SLC4A4 transporter NBCe1A
Author(s) -
Moss Fraser John,
Boron Walter F
Publication year - 2012
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.26.1_supplement.882.4
Subject(s) - carbonic anhydrase ii , chemistry , cytosol , carbonic anhydrase , transporter , homeostasis , cotransporter , biophysics , biochemistry , biology , enzyme , microbiology and biotechnology , sodium , organic chemistry , gene
The carbonic anhydrase II (CAII) metabolon hypothesis predicts that CAII binds to the electrogenic Na/HCO 3 co‐transporter (NBCe1), enhancing its transport of HCO 3 − ‐related species. In 2006, using a short I–V protocol (60 ms steps from the reversal potential E rev , 20 mV increments), the Boron Lab (BL) showed that neither pure CAII injected into Xenopus oocytes expressing NBCe1 nor CAII fused to the NBCe1 C‐terminus (Ct) changed NBCe1 slope conductance (G). Yet in 2007, using long I–V protocol steps and a holding potential (V h ) tens of mV from E rev , Becker & Deitmer (BD) concluded the opposite. We hypothesized that the CAII in the cytosol (rather than that attached to the membrane) enhanced transport in the BD protocol by dissipating long‐distance HCO 3 − and pH i gradients—an effect that should be accentuated by long V h steps far from E rev . We found G was unchanged even after increasing V h steps to 30 s, whether CAII was injected in the cytosol or fused to the NBCe1‐Ct. In fact, replicating the entire BD protocol detected no significant CAII‐mediated change in peak NBCe1 current (ΔI) or G. Even when NBCe1 was driven to near‐maximal activity by setting V h at 0 mV, CAII did not enhance the recovery rate from CO 2 ‐induced acidification, NBCe1 ΔI or G. These data contradict the metabolon hypothesis. We continue to test if the source of CAII protein or if NBCe1A expression levels can yield systematic differences in the effect of CAII on G.