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pH sensitivity of ammonium transport by Rhbg
Author(s) -
Nakhoul Nazih L,
AbdulnourNakhoul Solange,
Schmidt Eric,
Doetjes Rienk,
Hamm L Lee
Publication year - 2007
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.21.6.a1338-c
Subject(s) - chemistry , biophysics , depolarization , ammonium , xenopus , membrane potential , ion transporter , membrane , biochemistry , biology , organic chemistry , gene
Rhbg, a non‐erythroid glycoprotein, is localized to the basolateral membrane of renal intercalated cells and is involved in NH 4 + transport. In this study we characterized the pH sensitivity of Rhbg expressed in Xenopus oocytes. We used two‐electrode voltage clamp & ion‐selective microelectrodes to measure NH 4 + currents (I NH4+ ) & changes in pH i . In oocytes expressing Rhbg, 5mM NH 4 + induced an inward I NH4+ of −79 nA, decreased pH i by 0.13 at a rate of −27×10 −4 pH/sec & depolarized the cell by 45 mV. These changes were significantly larger than in H 2 O‐injected oocytes. Methyl ammonium (MA, 5 mM), often used as an NH 4 + substrate, induced a current (I MA ) of −63 nA in Rhbg oocytes but did not cause any change in control oocytes. Unlike NH 4 + , MA elicited a pH i increase but also induced a depolarization of the cell. Exposing the oocyte to MA at alkaline bath pH (8.2) enhanced both the pH i increase & I MA . Lowering bath pH to 6.5 inhibited the MA‐induced changes completely. The NH 4 + ‐induced changes in pH i & current were similarly sensitive to pH. Exposing the oocyte to MA at low pH i (decreased by butyrate) abolished the MA‐induced current however pH i still increased. These data indicate that: Rhbg transport of NH 4 + is electrogenic. MA transport by Rhbg is both electroneutral and electrogenic. Electrogenic NH 4 + and MA transport is pH sensitive. Electroneutral transport of MA by Rhbg is not affected by pH changes.