Gonçalves P P, Carvalho A P
Departamento de Zoologia, Universidade de Coimbra, Portugal.
Neurochem Int. 1994 Nov;25(5):483-92. doi: 10.1016/0197-0186(94)90025-6.
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-.
研究了各种阴离子对从绵羊脑皮质分离的突触质膜（SPM）囊泡摄取和释放γ-氨基丁酸（GABA）的影响。我们观察到，用各种阴离子取代Cl-会大大降低SPM囊泡对[3H]GABA的积累。当Cl-分别被Br-、NO3-、CH3COO-和SO4(2-)取代时，这种效应的幅度分别约为30%、85%、95%和100%。然而，当这些阴离子与Cl-一起添加时未观察到影响，这表明它们不会抑制SPM囊泡对[3H]GABA的摄取机制。另一方面，我们观察到，无论是通过同源交换还是由K+去极化诱导的[3H]GABA释放，在Cl-或Br-存在时最大，而其他阴离子（NO3-、CH3COO-和SO4(2-)）会使[3H]GABA释放的两个过程减少50%。我们还观察到，[3H]GABA的基础释放不受Br-和NO3-的显著影响，但在取代Cl-时，CH3COO-和SO4(2-)会使其大大增强。与[3H]GABA运动的这些变化相反，膜电位不受所测试的任何阴离子的显著影响。结果证实了GABA摄取意味着Cl-共转运的观点，并且表明通过其载体最大程度地释放[3H]GABA（同源交换或K+去极化诱导的释放）需要在与神经递质转运相反的膜侧存在小阴离子（Cl-或Br-）。此外，似乎CH3COO-和SO4(2-)通过诱导基础释放使系统解偶联，而在Cl-、Br-和NO3-存在时系统仍保持偶联。
