COMPARISON OF THE SUPERFUSED EFFLUX OF PREACCUMULATED D-[H-3]ASPARTATE AND ENDOGENOUS L-ASPARTATE AND L-GLUTAMATE FROM RAT CEREBROCORTICAL MINISLICES

Because the validity of the use of preaccumulated isotopic excitatory amino acids (EAAs) to index the depolarization-evoked release of endogenous EAAs has been questioned, we compared the K+ evoked efflux of preaccumulated D-[H-3]aspartate from rat cerebrocortical minislices with that of endogenous L-aspartate and L-glutamate. Release of all EAAs increased with the rate of superfusion. Using the most rapid rate (1.6 ml/min), transient elevations in [K+] caused a concentration-dependent. increase, with 50 mM K+ evoking a 33-, 23- and 93-fold increase in the efflux of D-[H-3]aspartate, L-aspartate and L-glutamate, respectively; this efflux was Ca2+-dependent and tetrodotoxin insensitive. Under polarized conditions (5 mM K+), 1 mM kainic acid increased the efflux of preaccumulated and endogenous EAAs. These elevations were not blocked by the competitive kainate receptor antagonist 6,7-dinitroquinoxaline-2-3-dione (DNQX) and were not affected by removing Ca2+ ions. We conclude that in superfused cortical minislices, the efflux of preaccumulated D-[H-3]aspartate provides a robust and reliable index of the release of endogenous L-aspartate and L-glutamate.