Effect of ammonia on amino acid uptake by brain microvessels

J Biol Chem. 1984 Apr 25;259(8):5295-300.

Abstract

NH+4 ions, at a concentration (0.25 mM) similar to that found in the plasma of patients with hepatic encephalopathy, cause, in vitro, a significant stimulation of the uptake by brain microvessels of large neutral amino acids, without any effect on the uptake of alpha-methylaminoisobutyric acid, glutamic acid, or lysine. Such a stimulation occurs essentially through an increase of the maximal transport capacity (Vmax) of the saturable component. It is apparently mediated by the intracellular formation of glutamine, which is then exchanged, through the L-system of transport, for large neutral amino acids such as leucine, phenylalanine, or tyrosine. At higher concentrations (greater than or equal to 0.5 mM), NH+4 ions cause also a decrease of carrier affinity for neutral amino acids, which counteracts the stimulatory effect on their uptake.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 2,4-Dinitrophenol
  • Adenosine Triphosphate / metabolism
  • Amino Acids / metabolism*
  • Ammonia / pharmacology*
  • Animals
  • Biological Transport / drug effects
  • Brain / blood supply*
  • Cattle
  • Dinitrophenols / pharmacology
  • Kinetics
  • Microcirculation / drug effects
  • Microcirculation / metabolism*
  • Microcirculation / ultrastructure
  • Microscopy, Electron, Scanning

Substances

  • Amino Acids
  • Dinitrophenols
  • Ammonia
  • Adenosine Triphosphate
  • 2,4-Dinitrophenol