EFFECT OF ANIONS ON THE UPTAKE AND RELEASE OF GAMMA-AMINOBUTYRIC-ACID BY ISOLATED SYNAPTIC PLASMA-MEMBRANES

The influence of various anions on the uptake and release of gamma-aminobutyric acid (GABA) was investigated in synaptic plasma membrane (SPM) vesicles isolated from sheep brain cortex. We observed that substitution of Cl- by various anions greatly reduces [H-3]GABA accumulation by SPM vesicles. The magnitude of the effect is about 30, 85, 95 and 100% when Cl- is replaced by Br-, NO3-, CH3COO- and SO42-, respectively. However, no effect was observed when these anions were added together with Cl-, which indicates that they do not inhibit the [H-3]GABA uptake mechanism by SPM vesicles. On the other hand, we observed that [H-3]GABA release, either by homoexchange or induced by K+ depolarization, is maximal in the presence of Cl- or Br- whereas the other anions (NO3-, CH3COO- and SO42-) caused a 50% reduction in the two processes of [H-3]GABA release. We also observed that the basal release of [H-3]GABA is not greatly altered by Br- and NO3-, but it is greatly enhanced by CH3COO- and SO42- in substitution of Cl-. In contrast to these alterations in [H-3]GABA movements, the membrane potential is not significantly affected by any of the anions tested. The results confirm the idea that GAB,4 uptake implies Cl- co-transport and they demonstrate that the maximal release of [H-3]GABA through its carrier (homoexchange or K+ depolarization-induced release) requires the presence of small anions (Cl- or Br-) al the opposite side of the membrane from where the neurotransmitter is translocated. Furthermore, it appears that CH3COO- and SO42- uncouple the system by inducing basal release, whereas it remains coupled in the presence of Cl-, Br- and NO3-.