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NH 4 + as a substrate for apical and basolateral Na + ‐H + exchangers of thick ascending limbs of rat kidney: evidence from isolated membranes
Author(s) -
Blanchard Anne,
Eladari Dominique,
Leviel Françoise,
Tsimaratos Michel,
Paillard Michel,
Podevin RenéAlexandre
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.689bv.x
Subject(s) - chemistry , antiporter , amiloride , vesicle , membrane , dissociation constant , membrane transport , symporter , sodium–hydrogen antiporter , ion exchange , ion transporter , biophysics , antiporters , dissociation (chemistry) , analytical chemistry (journal) , sodium , biochemistry , ion , chromatography , biology , receptor , transporter , organic chemistry , gene
1 We have used highly purified right‐side‐out luminal and basolateral membrane vesicles (LMVs and BLMVs) isolated from rat medullary thick ascending limb (MTAL) to study directly the possible roles of the LMV and BLMV Na + ‐H + exchangers in the transport of NH 4 + . 2 Extravesicular NH 4 + ((NH 4 + ) o ) inhibited outward H + gradient‐stimulated 22 Na + uptake in both types of vesicles. This inhibition could not be accounted for by alteration of intravesicular pH (pH i ). 3 Conversely, in both plasma membrane preparations, the imposition of outward NH 4 + gradients stimulated 22 Na + uptake at the acidic pH i (6.60) of MTAL cells, under conditions in which possible alterations in pH i were prevented. All NH 4 + gradient‐stimulated Na + uptake was sensitive to 0.5 mM 5‐( N,N ‐dimethyl)‐amiloride. 4 The BLMV and LMV Na + ‐H + exchangers had a similar apparent affinity for internal H + (H + i ), with p K (‐log of dissociation constant) values of 6.58 and 6.52, respectively. 5 These findings indicate that NH 4 + interacts with the external and internal transport sites of the LMV and BLMV Na + ‐H + antiporters, and that both of these exchangers can mediate the exchange of internal NH 4 + ((NH 4 + ) i ) for external Na + (Na + o ) at the prevailing pH i of MTAL cells. 6 We conclude that operation of the BLMV Na + ‐H + exchanger on the NH 4 + ‐Na + mode may represent an important pathway for mediating the final step of NH 4 + absorption, whereas transport of NH 4 + on the apical antiporter may provide negative feedback regulation of NH 4 + absorption.