Evoked release of aspartate and glutamate: disparities between prelabeling and direct measurement.

Slices prepared from hippocampus were dual prelabeled with [14C]L-glutamate and [3H]D-aspartate and superfused in the presence or absence of kainic acid (KA; 1 mM) or KCl (40 mM). Drug-evoked release of radioactivity as well as the endogenous amino acids, glutamate and aspartate were determined. Whereas KCl-induced a Ca2+-dependent release of all compounds, only the release of the endogenous amino acids was stimulated by KA. The results of the present study demonstrate that disparities exist between the Ca2+-dependent drug-evoked release of exogenously supplied and endogenous acidic amino acid neurotransmitters.