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Structural requirements for the electrogenicity of the electrogenic Na‐HCO3 cotransporter NBCe1
Author(s) -
Chen LiMing,
Boron Walter F
Publication year - 2008
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.22.1_supplement.759.13
Subject(s) - cotransporter , chemistry , reabsorption , xenopus , hyperpolarization (physics) , extracellular , transmembrane domain , biophysics , medicine , microbiology and biotechnology , biochemistry , biology , receptor , sodium , stereochemistry , nuclear magnetic resonance spectroscopy , gene , organic chemistry
Na/HCO 3 cotransporters, including the electrogenic NBCe1 and the electroneutral NBCn1, belong to SLC4 family. The NBCe1‐A splicing variant plays a key role in HCO 3 reabsorption by renal proximal tubules. NBCe1 and NBCn1 have 13 putative transmembrane (TM) segments and a large extracellular loop between TM5 and 6 (“the Loop”). Choi et al (J Physiol, 578:131, 2007) previously demonstrated that the electrogenecity of NBCe1‐A requires the interaction between TM1‐5 and TM6‐13, but does not require the cytoplasmic N terminus (Nt), the Loop, or the cytoplasmic C terminus (Ct). To understand better the structural basis of electrogenecity of NBCe1, we constructed a series of chimeras of human NBCe1‐A and NBCn1‐X (i.e., lacking cassette B in the Ct), starting with one consisting of Nt∼Loop of NBCe1‐A spliced to TM6∼Ct of NBCn1. We exposed Xenopus oocytes expressing chimeras or wild‐type NBCe1‐A to 1.5% CO 2 /10 mM HCO 3 (pH 7.5), and monitored pH i and V m . We found that this first chimera exhibits the Na conductance characteristic of NBCn1, but no HCO 3 transport. Restoring TM6‐7 of NBCe1‐A restored some electrogenic HCO 3 transport (i.e., CO 2 /HCO 3 elicited a slight hyperpolarization and pH i recovery). The chimera in which we restored TM6‐9 of NBCe1‐A functions as a typical NBCe1‐A. We conclude that the putative TM6‐9 of NBCe1 (vs NBCn1) is very important, but TM10‐13 of NBCe1 is not essential, for the electrogenecity of NBCe1‐A.