EFFLUX OF PHENYLALANINE FROM RAT CEREBRAL-CORTEX SLICES AS INFLUENCED BY EXTRACELLULAR AND INTRACELLULAR AMINO-ACIDS

Abstract— Effects of other amino acids on the efflux of l‐[3H]phenylalanine from rat cerebral cortex slices were studied in a superfusion system. Extracellular large neutral amino acids caused a strong trans‐stimulation of [3H]phenylalanine efflux. Some small neutral amino acids were less effective, whereas acidic and basic amino acids and the amino acids without an amino group in the α‐position were ineffective. Any trans‐inhibition was not detected. The stimulatory trans‐effects of phenylalanine and tryptophan were additive, reversible and concentration‐dependent. They were apparently mediated by the same mechanisms. The efflux of [3H]phenylalanine was much slower at 273 K than at 310 K, but the effects of unlabelled phenylalanine and tryptophan on it were qualitatively similar at both temperatures. Amino acids accumulated intracellularly at moderately high concentrations did not inhibit [3H]phenylalanine efflux, but phenylalanine, leucine, isoleucine and norleucine caused an enhancement. Spontaneous efflux of [3H]phenylalanine showed some similarities to physical diffusion, but its selective and specific modification by other amino acids strongly suggests the involvement of mediated processes. Copyright © 1979, Wiley Blackwell. All rights reserved