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 [3H]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 SO4(2-), respectively. However, no effect was observed when these anions were added together with Cl-, which indicates that they do not inhibit the [3H]GABA uptake mechanism by SPM vesicles. On the other hand, we observed that [3H]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 SO4(2-)) caused a 50% reduction in the two processes of [3H]GABA release. We also observed that the basal release of [3H]GABA is not greatly altered by Br- and NO3-, but it is greatly enhanced by CH3COO- and SO4(2-) in substitution of Cl-. In contrast to these alterations in [3H]GABA movements, the membrane potential is not significantly affected by any of the anions tested. The results confirm the idea that GABA uptake implies Cl- co-transport and they demonstrate that the maximal release of [3H]GABA through its carrier (homoexchange or K+ depolarization-induced release) requires the presence of small anions (Cl- or Br-) at the opposite side of the membrane from where the neurotransmitter is translocated. Furthermore, it appears that CH3COO- and SO4(2-) uncouple the system by inducing basal release, whereas it remains coupled in the presence of Cl-, Br- and NO3-.
Gonçalves
P P
PP
Departamento de Zoologia, Universidade de Coimbra, Portugal.
Carvalho
A P
AP
D000818:Animals; D000838:Anions / Q000378:metabolism*; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials; D012756:Sheep; D013570:Synaptic Membranes / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000838:Anions; D002712:Chlorides; D005680:gamma-Aminobutyric Acid