AJP - Renal Fuel your research with LabChart
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Renal Physiol 253: F959-F968, 1987;
0363-6127/87 $5.00
This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Goldfarb, D.
Right arrow Articles by Nord, E. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Goldfarb, D.
Right arrow Articles by Nord, E. P.

AJP - Renal Physiology, Vol 253, Issue 5 959-F968, Copyright © 1987 by American Physiological Society

ARTICLES

Asymmetric affinity of Na+-H+ antiporter for Na+ at the cytoplasmic versus external transport site

D. Goldfarb and E. P. Nord
Department of Medicine, University of California, School of Medicine, Los Angeles 90024.

The affinity for Na+ of the cytoplasmic vs. external transport site of the amiloride-sensitive Na+-H+ antiporter was studied in confluent cultures of MDCK cells. Na+-H+ antiport activity was fluorometrically determined by monitoring changes in intracellular pH (pHi) using the pH-sensitive fluorescent probe, BCECF. Na+-dependent H+ fluxes were studied both in the functionally operative (H+ efflux/Na+ influx) and reverse (H+ influx/Na+ efflux) mode of antiport activity, under pH equilibrium, but Na+-gradient conditions. Thus the driving force for antiport activity was solely dependent on the transmembrane Na+ gradient. Independent experiments established that pHi and intracellular Na+ [Na+i] had been set at the desired values before the initiation of a particular experiment. Under conditions of pHi = pHo = 7.0, [Na+i] = 0 mM and varying extracellular Na+ concentration [Na+o], the apparent affinity for Na+ (KtNa) for the external transport site was 24 +/- 3 mM. When antiport activity was measured in the reverse mode of operation, but under identical pH conditions, KtNa at the internal site was 7 +/- 1 mM. When ambient pH was elevated to 7.5, KtNa at the internal site was 14 +/- 1 mM. Maximum H+ flux (JmaxH+) for the antiporter under all three conditions was not significantly different. In summary, the Na+-H+ antiporter displays asymmetric affinity for Na+ at the internal vs. external transport site. Under pH equilibrium conditions, the affinity of the Na+-H+ antiporter for Na+ is three- to four-fold greater at the internal vs. external locus, and the affinity for Na+ at the internal site is enhanced by lower pHi. The close similarity between values for KtNa (inside) and reported values for intracellular Na+ concentration suggests that regulation of the Na+-H+ antiporter may be affected by changes in intracellular Na+ concentration.


This article has been cited by other articles:


Home page
 Am. J. Physiol. Renal Physiol.Home page
M. Oliveira-Souza and M. De Mello-Aires
Interaction of angiotensin II and atrial natriuretic peptide on pHi regulation in MDCK cells
Am J Physiol Renal Physiol, November 1, 2000; 279(5): F944 - F953.
[Abstract] [Full Text] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online