Release of Endogenous and Accumulated Exogenous Amino Acids from Slices of Normal and Climbing Fibre-Deprived Rat Cerebellar Slices

Abstract

Efflux of various amino acids from slices of rat cerebellar hemispheres was determined under resting or depolarizing conditions. It was increased under high K+(50 mM) as compared to low K+ (5 mM) conditions by 1258 pmol/mg protein for aspartate, 478 for GABA, 44,693 for glutamate, and 615 for glycine. These were significantly higher than the corresponding values obtained under low-Ca2+ (0.1 mM), high-Mg2+ (12 mM) conditions, whereas for 11 other amino acids the K+-induced efflux was similar under normal and low-Ca2+ concentrations. The K+-induced efflux of exogenously accumulated L-[3H]aspartate, D-[3H]aspartate, and L-[3H]glutamate was higher by factors of 2, 5.8 and 6.3, respectively, under normal Ca2+ conditions, as compared with low-Ca2+, high-Mg2+ conditions. AFter climbing fiber degeneration induced by destruction of the inferior olive with 3-acetylpyridine, release of endogenous aspartate and exogenous L-[3H]glutamate and D-[3H]aspartate was significantly reduced, by 26%, 38%, and 27%, respectively. Climbing fibers may use aspartate or a related compound as a neurotransmitter. In rat cerebellar tissue, L-[3H]glutamate and L-[3H]aspartate differ in several aspects: L-[3H]glutamate uptake was 4 times higher than that of L-[3H]aspartate; fractional rate constant of K+-evoked release of L-[3H]aspartate was 7% .times. 2.5 min-1, and of L-[3H]glutamate 36% .times. 2.5 min-1; and specific activity of L-[3H]glutamate in the eluate collected during K+ stimulation was 3.5 times the value in the tissue, whereas, for L-[3H]aspartate, specific activities in the eluate and tissue were similar.