EFFECT OF ELECTRICAL STIMULATION AND CHLORPROMAZINE ON THE UPTAKE AND RELEASE OF TAURINE, γ‐AMINOBUTYRIC ACID AND GLUTAMIC ACID IN MOUSE BRAIN SYNAPTOSOMES

Abstract

Abstract —The concentrations of taurine and GABA were determined in isolated mouse brain synaptosomes incubated in Krebs‐Ringer phosphate medium (pH 7·4). The concentration of GABA gradually decreased during incubation, but that of taurine remained approximately unchanged. In the presence of chlorpromazine the amount of GABA in the synaptosomes increased, but the efflux and influx of GABA were slightly reduced. The content and efflux of both taurine and GABA increased in electrically stimulated synaptosomes, and the influx of taurine, GABA and glutamate into the synaptosomes similarly increased. All three amino acids are taken up by the synaptosomes through at least two mechanisms: low‐affinity and high‐affinity. In the high‐affinity system the K m values were 33 μ m for taurine, 24 μ m for GABA and 68 μ m for glutamate, and in the low‐affinity one 1·1 mil, 0·9 m m and 1·2m m , respectively. The influx capacity ( V max ) was highest for glutamate, second highest for GABA and lowest for taurine.