Enhancement of [3H]glutamate binding by N-methyl-D-aspartic acid in rat adrenal.

Some neurochemical characteristics of [3H]L-glutamic acid binding sites were studied using membranous homogenate preparations obtained from the rat adrenal. It was found that the binding was inhibited by the addition (10(-7)-10(-3) M) of L-isomers of structure-related compounds in a concentration-dependent manner. A significant inhibition of the binding was induced by L-glutamic acid diethylester, but not by alpha-aminoadipic acid. Scatchard analysis revealed that the binding sites consisted of a single component with a Kd of 0.19 +/- 0.05 microM and a Bmax of 4.11 +/- 0.71 pmol/mg protein, respectively. In vitro addition of sodium acetate (1-100 mM) elicited a stimulatory action on the binding at 2 degrees C, while inducing a significant attenuation of the binding at 30 degrees C. The binding reached a plateau within 30 min of incubation followed by a gradual decline up to 60 min in the presence of 100 mM sodium acetate at 30 degrees C, whereas the binding continued to increase up to 60 min in the absence of sodium acetate. Addition (0.1-10 mM) of N-methyl-D-aspartic acid (NMDA), one of the agonists for central excitatory amino acid neurotransmitter receptors, exerted a significant augmentation of the adrenal binding independently of the incubation temperature in a concentration-dependent manner. The latter facilitation of the binding, however, was not affected by the classical antagonists for central NMDA receptors such as 2-amino-5-phosphonovaleric acid and 2-amino-7-phosphonoheptanoic acid.(ABSTRACT TRUNCATED AT 250 WORDS)