Active absorption of NH4 + by rat medullary thick ascending limb

Inhibition by potassium

Research output: Contribution to journalArticle

63 Citations (Scopus)

Abstract

These experiments were designed to determine the relative contributions of active NH4 + transport and voltage-driven NH4 + diffusion to direct NH4 + absorption by the medullary thick ascending limb of the rat. Medullary thick ascending limbs were perfused in vitro with solutions containing 25 mM HCO3 and 4 mM total ammonia. Under steady-state conditions, the lumen-positive transepithelial voltage (V(T)) was not sufficient to account for the observed decrease in lumen NH4 + concentration, consistent with active absorption of NH4 +. Flux calculations based on V(T) and measured NH4 + permeability (6 x 10-5 cm/s) indicate that the majority (at least 65%) of total ammonia absorption is due to active transport of NH4 +. The remainder of NH4 + absorption can be accounted for by voltage-driven diffusion. Increasing the potassium concentration from 4 to 24 mM in perfusate and bath markedly inhibited total ammonia absorption but did not affect V(T), NH4 + permeability, or HCO3 absorption. These results are consistent with inhibition of the active component of NH4 + absorption by potassium. The active NH4 + absorption is likely mediated by cotransport of Na+, NH4 +, and Cl- across the apical cell membrane. Inhibition of active NH4 + absorption by an increase in potassium concentration may be due, in part, to competition between NH4 + and K+ for a common binding site on the Na+-K+-2Cl- cotransport system.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Volume255
Issue number1
StatePublished - 1988

Fingerprint

Potassium
Extremities
Ammonia
Active Biological Transport
Permeability
Baths
Binding Sites
Cell Membrane

ASJC Scopus subject areas

  • Physiology

Cite this

@article{667cf112823a4d5ea3320d3b2369d086,
title = "Active absorption of NH4 + by rat medullary thick ascending limb: Inhibition by potassium",
abstract = "These experiments were designed to determine the relative contributions of active NH4 + transport and voltage-driven NH4 + diffusion to direct NH4 + absorption by the medullary thick ascending limb of the rat. Medullary thick ascending limbs were perfused in vitro with solutions containing 25 mM HCO3 and 4 mM total ammonia. Under steady-state conditions, the lumen-positive transepithelial voltage (V(T)) was not sufficient to account for the observed decrease in lumen NH4 + concentration, consistent with active absorption of NH4 +. Flux calculations based on V(T) and measured NH4 + permeability (6 x 10-5 cm/s) indicate that the majority (at least 65{\%}) of total ammonia absorption is due to active transport of NH4 +. The remainder of NH4 + absorption can be accounted for by voltage-driven diffusion. Increasing the potassium concentration from 4 to 24 mM in perfusate and bath markedly inhibited total ammonia absorption but did not affect V(T), NH4 + permeability, or HCO3 absorption. These results are consistent with inhibition of the active component of NH4 + absorption by potassium. The active NH4 + absorption is likely mediated by cotransport of Na+, NH4 +, and Cl- across the apical cell membrane. Inhibition of active NH4 + absorption by an increase in potassium concentration may be due, in part, to competition between NH4 + and K+ for a common binding site on the Na+-K+-2Cl- cotransport system.",
author = "David Good",
year = "1988",
language = "English (US)",
volume = "255",
journal = "American Journal of Physiology - Endocrinology and Metabolism",
issn = "0193-1849",
publisher = "American Physiological Society",
number = "1",

}

TY - JOUR

T1 - Active absorption of NH4 + by rat medullary thick ascending limb

T2 - Inhibition by potassium

AU - Good, David

PY - 1988

Y1 - 1988

N2 - These experiments were designed to determine the relative contributions of active NH4 + transport and voltage-driven NH4 + diffusion to direct NH4 + absorption by the medullary thick ascending limb of the rat. Medullary thick ascending limbs were perfused in vitro with solutions containing 25 mM HCO3 and 4 mM total ammonia. Under steady-state conditions, the lumen-positive transepithelial voltage (V(T)) was not sufficient to account for the observed decrease in lumen NH4 + concentration, consistent with active absorption of NH4 +. Flux calculations based on V(T) and measured NH4 + permeability (6 x 10-5 cm/s) indicate that the majority (at least 65%) of total ammonia absorption is due to active transport of NH4 +. The remainder of NH4 + absorption can be accounted for by voltage-driven diffusion. Increasing the potassium concentration from 4 to 24 mM in perfusate and bath markedly inhibited total ammonia absorption but did not affect V(T), NH4 + permeability, or HCO3 absorption. These results are consistent with inhibition of the active component of NH4 + absorption by potassium. The active NH4 + absorption is likely mediated by cotransport of Na+, NH4 +, and Cl- across the apical cell membrane. Inhibition of active NH4 + absorption by an increase in potassium concentration may be due, in part, to competition between NH4 + and K+ for a common binding site on the Na+-K+-2Cl- cotransport system.

AB - These experiments were designed to determine the relative contributions of active NH4 + transport and voltage-driven NH4 + diffusion to direct NH4 + absorption by the medullary thick ascending limb of the rat. Medullary thick ascending limbs were perfused in vitro with solutions containing 25 mM HCO3 and 4 mM total ammonia. Under steady-state conditions, the lumen-positive transepithelial voltage (V(T)) was not sufficient to account for the observed decrease in lumen NH4 + concentration, consistent with active absorption of NH4 +. Flux calculations based on V(T) and measured NH4 + permeability (6 x 10-5 cm/s) indicate that the majority (at least 65%) of total ammonia absorption is due to active transport of NH4 +. The remainder of NH4 + absorption can be accounted for by voltage-driven diffusion. Increasing the potassium concentration from 4 to 24 mM in perfusate and bath markedly inhibited total ammonia absorption but did not affect V(T), NH4 + permeability, or HCO3 absorption. These results are consistent with inhibition of the active component of NH4 + absorption by potassium. The active NH4 + absorption is likely mediated by cotransport of Na+, NH4 +, and Cl- across the apical cell membrane. Inhibition of active NH4 + absorption by an increase in potassium concentration may be due, in part, to competition between NH4 + and K+ for a common binding site on the Na+-K+-2Cl- cotransport system.

UR - http://www.scopus.com/inward/record.url?scp=0023740459&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0023740459&partnerID=8YFLogxK

M3 - Article

VL - 255

JO - American Journal of Physiology - Endocrinology and Metabolism

JF - American Journal of Physiology - Endocrinology and Metabolism

SN - 0193-1849

IS - 1

ER -