Exchange and efflux of tryptophan from superfused cerebral cortex slices

The efflux and exchange of L-tryptophan (Trp) from rat cerebral cortex slices were studied in a superfusion system. The substrate specificity of Trp exchange was assessed by measuring the stimulation of [3H]Trp exit provoked by other extracellular amino acids. Large neutral amino acids were the most potent, but also glutamic acid, lysine and glycine had some effect. The stimulation caused by extracellular Trp and phenylalanine persisted also at 0 degrees C though severalfold attenuated. Only intracellular histidine provoked slight inhibition of [3H]Trp efflux and intracellular Trp, phenylalanine and lysine had a small stimulatory effect. The results suggest an involvement of carrier-mediated processes in the exchange and efflux of Trp. The substrate specificities of the exchange and efflux are not apparently identical.