Basolateral membrane Na+/H+ exchange enhances HCO- 3 absorption in rat medullary thick ascending limb

Evidence for functional coupling between basolateral and apical membrane Na+/H+ exchangers

David Good, Thampi George, Bruns Watts

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48 Citations (Scopus)

Abstract

The role of basolateral membrane Na+/H+ exchange in transepithelial HCO- 3 absorption (JHCO3) was examined in the isolated, perfused medullary thick ascending limb (MTAL) of the rat. In Na+-free solutions, addition of Na+ to the bath resulted in a rapid, amiloride-sensitive increase in intracellular pH. In MTALs perfused and bathed with solulions containing 146 mM Na+ and 25 mM HCO- 3, bath addition of amiloride (1 mM) or 5-(N-ethyl-N-isopropyl) amiloride (EIPA, 50 μM) reversibly inhibited JHCO3 by 50%. Evidence that the inhibition of JHCO3 by bath amiloride was the result of inhibition of Na+/H+ exchange included the following: (i) the IC50 for amiloride was 5-10 μM, (ii) EIPA was a 50-fold more potent inhibitor than amiloride, (iii) the inhibition by bath amiloride was Na+ dependent, and (iv) significant inhibition was observed with EIPA as low as 0.1 μM. Fifty micromolar amiloride or 1 μM EIPA inhibited JHCO3 by 35% when added to the bath but had no effect when added to the tubule lumen, indicating that addition of amiloride to the bath did not directly inhibit apical membrane Na+/H+ exchange. In experiments in which apical Na+/H+ exchange was assessed from the initial rate of cell acidification following luminal EIPA addition, bath EIPA secondarily inhibited apical Na+/H+ exchange activity by 46%. These results demonstrate that basolateral membrane Na+/H+ exchange enhances transepithelial HCO- 3 absorption in the MTAL. This effect appears to be the result of cross-talk in which an increase in basolateral membrane Na+/H+ exchange activity secondarily increases apical membrane Na+/H+ exchange activity.

Original languageEnglish (US)
Pages (from-to)12525-12529
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume92
Issue number26
StatePublished - Dec 19 1995

Fingerprint

Sodium-Hydrogen Antiporter
Amiloride
Baths
Extremities
Membranes
ethylisopropylamiloride
Inhibitory Concentration 50

Keywords

  • Amiloride
  • Cross-talk
  • Intracellular pH
  • Kidney
  • Renal acidification

ASJC Scopus subject areas

  • General
  • Genetics

Cite this

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title = "Basolateral membrane Na+/H+ exchange enhances HCO- 3 absorption in rat medullary thick ascending limb: Evidence for functional coupling between basolateral and apical membrane Na+/H+ exchangers",
abstract = "The role of basolateral membrane Na+/H+ exchange in transepithelial HCO- 3 absorption (JHCO3) was examined in the isolated, perfused medullary thick ascending limb (MTAL) of the rat. In Na+-free solutions, addition of Na+ to the bath resulted in a rapid, amiloride-sensitive increase in intracellular pH. In MTALs perfused and bathed with solulions containing 146 mM Na+ and 25 mM HCO- 3, bath addition of amiloride (1 mM) or 5-(N-ethyl-N-isopropyl) amiloride (EIPA, 50 μM) reversibly inhibited JHCO3 by 50{\%}. Evidence that the inhibition of JHCO3 by bath amiloride was the result of inhibition of Na+/H+ exchange included the following: (i) the IC50 for amiloride was 5-10 μM, (ii) EIPA was a 50-fold more potent inhibitor than amiloride, (iii) the inhibition by bath amiloride was Na+ dependent, and (iv) significant inhibition was observed with EIPA as low as 0.1 μM. Fifty micromolar amiloride or 1 μM EIPA inhibited JHCO3 by 35{\%} when added to the bath but had no effect when added to the tubule lumen, indicating that addition of amiloride to the bath did not directly inhibit apical membrane Na+/H+ exchange. In experiments in which apical Na+/H+ exchange was assessed from the initial rate of cell acidification following luminal EIPA addition, bath EIPA secondarily inhibited apical Na+/H+ exchange activity by 46{\%}. These results demonstrate that basolateral membrane Na+/H+ exchange enhances transepithelial HCO- 3 absorption in the MTAL. This effect appears to be the result of cross-talk in which an increase in basolateral membrane Na+/H+ exchange activity secondarily increases apical membrane Na+/H+ exchange activity.",
keywords = "Amiloride, Cross-talk, Intracellular pH, Kidney, Renal acidification",
author = "David Good and Thampi George and Bruns Watts",
year = "1995",
month = "12",
day = "19",
language = "English (US)",
volume = "92",
pages = "12525--12529",
journal = "Proceedings of the National Academy of Sciences of the United States of America",
issn = "0027-8424",
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TY - JOUR

T1 - Basolateral membrane Na+/H+ exchange enhances HCO- 3 absorption in rat medullary thick ascending limb

T2 - Evidence for functional coupling between basolateral and apical membrane Na+/H+ exchangers

AU - Good, David

AU - George, Thampi

AU - Watts, Bruns

PY - 1995/12/19

Y1 - 1995/12/19

N2 - The role of basolateral membrane Na+/H+ exchange in transepithelial HCO- 3 absorption (JHCO3) was examined in the isolated, perfused medullary thick ascending limb (MTAL) of the rat. In Na+-free solutions, addition of Na+ to the bath resulted in a rapid, amiloride-sensitive increase in intracellular pH. In MTALs perfused and bathed with solulions containing 146 mM Na+ and 25 mM HCO- 3, bath addition of amiloride (1 mM) or 5-(N-ethyl-N-isopropyl) amiloride (EIPA, 50 μM) reversibly inhibited JHCO3 by 50%. Evidence that the inhibition of JHCO3 by bath amiloride was the result of inhibition of Na+/H+ exchange included the following: (i) the IC50 for amiloride was 5-10 μM, (ii) EIPA was a 50-fold more potent inhibitor than amiloride, (iii) the inhibition by bath amiloride was Na+ dependent, and (iv) significant inhibition was observed with EIPA as low as 0.1 μM. Fifty micromolar amiloride or 1 μM EIPA inhibited JHCO3 by 35% when added to the bath but had no effect when added to the tubule lumen, indicating that addition of amiloride to the bath did not directly inhibit apical membrane Na+/H+ exchange. In experiments in which apical Na+/H+ exchange was assessed from the initial rate of cell acidification following luminal EIPA addition, bath EIPA secondarily inhibited apical Na+/H+ exchange activity by 46%. These results demonstrate that basolateral membrane Na+/H+ exchange enhances transepithelial HCO- 3 absorption in the MTAL. This effect appears to be the result of cross-talk in which an increase in basolateral membrane Na+/H+ exchange activity secondarily increases apical membrane Na+/H+ exchange activity.

AB - The role of basolateral membrane Na+/H+ exchange in transepithelial HCO- 3 absorption (JHCO3) was examined in the isolated, perfused medullary thick ascending limb (MTAL) of the rat. In Na+-free solutions, addition of Na+ to the bath resulted in a rapid, amiloride-sensitive increase in intracellular pH. In MTALs perfused and bathed with solulions containing 146 mM Na+ and 25 mM HCO- 3, bath addition of amiloride (1 mM) or 5-(N-ethyl-N-isopropyl) amiloride (EIPA, 50 μM) reversibly inhibited JHCO3 by 50%. Evidence that the inhibition of JHCO3 by bath amiloride was the result of inhibition of Na+/H+ exchange included the following: (i) the IC50 for amiloride was 5-10 μM, (ii) EIPA was a 50-fold more potent inhibitor than amiloride, (iii) the inhibition by bath amiloride was Na+ dependent, and (iv) significant inhibition was observed with EIPA as low as 0.1 μM. Fifty micromolar amiloride or 1 μM EIPA inhibited JHCO3 by 35% when added to the bath but had no effect when added to the tubule lumen, indicating that addition of amiloride to the bath did not directly inhibit apical membrane Na+/H+ exchange. In experiments in which apical Na+/H+ exchange was assessed from the initial rate of cell acidification following luminal EIPA addition, bath EIPA secondarily inhibited apical Na+/H+ exchange activity by 46%. These results demonstrate that basolateral membrane Na+/H+ exchange enhances transepithelial HCO- 3 absorption in the MTAL. This effect appears to be the result of cross-talk in which an increase in basolateral membrane Na+/H+ exchange activity secondarily increases apical membrane Na+/H+ exchange activity.

KW - Amiloride

KW - Cross-talk

KW - Intracellular pH

KW - Kidney

KW - Renal acidification

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M3 - Article

VL - 92

SP - 12525

EP - 12529

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

SN - 0027-8424

IS - 26

ER -