Journal of Neuroscience, Vol 5, 2882-2888, Copyright © 1985 by Society for Neuroscience
The characterization of the specific binding of [3H]-N- acetylaspartylglutamate to rat brain membranes
KJ Koller and JT Coyle
[3H]-N-Acetylaspartylglutamate (NAAG) bound saturably and reversibly to
crude synaptosomal rat brain membranes. Optimal binding occurred in
Tris-HCl buffer, pH 7.2, at 37 degrees C using previously frozen,
preincubated membranes. Saturation experiments revealed an apparent KD of
383 +/- 33 nM and a Bmax of 31 +/- 2 pmol/mg of protein. [3H]NAAG specific
binding was displaceable by serine-o-sulfate, quisqualate, ibotenate, and
glutamate with K1's in the nanomolar range, whereas the amino-phosphono
analogues displaced [3H] NAAG in the micromolar range (APB greater than APV
greater than APH). No specific binding was found in peripheral tissues.
Within the central nervous system, the thalamus exhibited the greatest
amount of binding, whereas binding was lowest in cortex. Calcium ions
enhanced the specific binding, whereas sodium ions caused a
concentration-dependent inhibition. These results suggest that [3H]NAAG
labels an acidic amino acid receptor site designated "A-4," which
recognizes the antagonist, 2-amino-4-phosphonobutyric acid, and that this
receptor may mediate the neurophysiologic effects of endogenous NAAG.