Studies on the mechanism by which tryptophan efflux from isolated synaptosomes is stimulated by depolarization

Abstract

1 The efflux and influx of tryptophan across the synaptosomal plasma membrane has been studied under a variety of experimental conditions, in order to examine the mechanism by which depolarization enhances the efflux of tryptophan from superfused synaptosomes. 4 Influx of [3H]-tryptophan into synaptosomes was stimulated by extracellular Na+ removal, but the uptake of [3H]-phenylalanine was unaffected by this procedure. 5 Both the induced influx and efflux of tryptophan observed under these experimental conditions was inhibited by immobilizing the plasma membrane carrier with parachlorophenylalanine. This implied that both the enhanced influx and efflux arose as a consequence of the activation of the membrane tryptophan carrier, the direction of the observed effect being dependent upon the manner in which the experiments were conducted. 6 The relationship between depolarization, the activation of the membrane tryptophan carrier and the significance of this to the in vivo situation is discussed.

Synaptosomal tryptophan uptake and efflux following lesion of central 5‐hydroxytryptaminergic neurones

“…However, the major purpose of the study was to study the effect of the lesions on the stimulation of tryptophan uptake by decreasing extracellular Na+. The experimental protocol used was essentially the same whether the uptake of [3H]-5-HT or [3H]-L-tryptophan was being examined, and was based on methods previously used in this laboratory (Wilkinson & Collard, 1984;Collard et al, 1988). Each synaptosomal preparation was divided into two fractions before the final centrifugation.…”