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Sodium/Bicarbonate Transporter NBCn1 (SLC4A7) Reduces Ammonium Transport
Author(s) -
LEE SOOJUNG,
CHOI INYEONG
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.1041.48
Subject(s) - xenopus , cotransporter , intracellular ph , chemistry , ammonium , biophysics , ammonium chloride , membrane potential , intracellular , medicine , endocrinology , biology , sodium , biochemistry , organic chemistry , gene
NH 4 + and HCO 3 − transport processes are closely associated with each other in the renal medullary thick ascending limb, where the electroneutral Na/HCO 3 cotransporter NBCn1 is present. In this study, we examined the effect of NBCn1 on NH 4 + transport. NBCn1 was expressed in Xenopus oocytes, and its contribution to NH 4 + transport was determined by measuring intracellular pH (pHi) and currents. In CO 2 /HCO 3 − ‐free solution, 20 mM NH 4 Cl caused the membrane potential to positively shift by 2.2 ± 0.2 mV (n = 6) in NBCn1‐expressing oocytes. This shift was significantly smaller than 23.9 ± 3.9 mV (n = 6) for water‐injected control oocytes. Ammonium chloride induced a slow decrease in pHi in NBCn1‐expressing oocytes, similar to a decrease in control oocytes. Under voltage‐clamp conditions, NBCn1‐expressing oocytes produced negligible currents after NH 4 Cl application, whereas control oocytes produced robust inward currents. The lack of NH 4 + currents in NBCn1‐expressing oocytes was time‐dependent: the currents were progressively reduced as NBCn1 expression was increased over time. In the presence of 5% CO 2 , 25 mM HCO 3 − , NBCn1‐expressing oocytes showed a slow decrease in pHi after NH 4 Cl application compared to controls. We conclude that NBCn1 reduces NH 4 + transport in Xenopus oocytes. Our results are significant for providing novel evidence that NBCn1 inhibits NH 4 + transport by the cotransport‐independent mechanism.