Ammonium transport in medullary thick ascending limb of rabbit kidney: involvement of the Na+,K+,Cl(-)-cotransporter

J Membr Biol. 1986;94(3):279-84. doi: 10.1007/BF01869723.


In order to investigate the question whether ammonium reabsorption in the thick ascending limb of Henle's loop (TALH) proceeds via the Na+,K+,Cl(-)-cotransporter, plasma membrane vesicles were prepared from TALH cells isolated from rabbit kidney outer medulla and the effect of NH+4 on their transport properties was investigated. It was found that, in the presence of a 78-mmol/liter NaCl gradient, 5 mmol/liter NH+4 inhibited bumetanide-sensitive rubidium flux by 86%; a similar decrease was observed for 5 mmol/liter, K+. Inhibition of bumetanide-sensitive rubidium uptake by NH+4 was competitive and an apparent Ki of 1.9 mmol/liter was found. Bumetanide-sensitive sodium uptake measured in the presence of a 83 mmol/liter KCl gradient was not inhibited by 5 mmol/liter NH+4. A 100-mmol/liter NH4Cl gradient was, however, capable of stimulating bumetanide-sensitive sodium uptake to the same extent as a KCl gradient. These data suggest that NH+4 is accepted by the K+ site of the Na+,K+,Cl-cotransport system and that the transporter can function in a Na+,NH+4,2Cl mode. Since the affinity of the transporter for NH+4 lies in the concentration range found in the TALH lumen in vivo, it is concluded that Na+,NH+4,2Cl-cotransport can contribute to the NH+4 reabsorption in this tubular segment.

MeSH terms

  • Ammonia / metabolism*
  • Animals
  • Biological Transport, Active / drug effects
  • Bumetanide / pharmacology
  • Carrier Proteins / metabolism*
  • Cell Membrane / metabolism
  • Chlorides / metabolism*
  • In Vitro Techniques
  • Kidney Medulla / metabolism*
  • Kidney Tubules / metabolism*
  • Kinetics
  • Loop of Henle / metabolism*
  • Membrane Proteins / metabolism*
  • Potassium / metabolism*
  • Rabbits
  • Rubidium / metabolism
  • Sodium / metabolism*
  • Sodium-Potassium-Chloride Symporters


  • Carrier Proteins
  • Chlorides
  • Membrane Proteins
  • Sodium-Potassium-Chloride Symporters
  • Bumetanide
  • Ammonia
  • Sodium
  • Rubidium
  • Potassium