Cha J H, O'Brien D R, Dowling J E
Brain Res. 1986 Jun 18;376(1):140-8. doi: 10.1016/0006-8993(86)90908-x.
The rate of release of [3H]GABA from isolated intact goldfish retinas was studied. Release of [3H]GABA is markedly stimulated by the inclusion in the incubation medium of the photoreceptor neurotransmitter candidates L-glutamate (L-Glu) and L-aspartate (L-Asp), and the glutamate analogs, kainate and quisqualate. At micromolar concentrations, kainate and quisqualate are effective releasers of [3H]GABA, whereas millimolar concentrations of L-Glu and L-Asp are required to release comparable amounts of [3H]GABA. The D-isomers of aspartate (D-Asp) and glutamate (D-Glu) are able to release [3H]GABA, but only when applied at high concentrations (3-30 mM). In the presence of 5 mM D-Asp, the effect of L-Glu in releasing [3H]GABA was markedly potentiated. This dose-response curve of L-Glu was shifted to the left in the presence of D-Asp, although the maximal amount of release was unchanged. D-Asp at 5 mM only slightly increased the GABA release induced by quisqualate, and it did not increase the GABA release induced by kainate. Finally, low concentrations of L-Asp were potentiated by D-Asp, but higher concentrations of L-Asp (3-10 mM) were clearly inhibited by this agent. This biphasic effect of D-Asp on L-Asp-induced release of [3H]GABA is a possible explanation for previously conflicting reports of D-Asp's effect on L-Asp action. Our data suggest that D-Asp has both pre- and postsynaptic sites of action.
研究了从分离的完整金鱼视网膜中释放[3H]γ-氨基丁酸（GABA）的速率。在孵育培养基中加入光感受器神经递质候选物L-谷氨酸（L-Glu）、L-天冬氨酸（L-Asp）以及谷氨酸类似物 kainate 和 quisqualate 时，[3H]GABA 的释放受到显著刺激。在微摩尔浓度下，kainate 和 quisqualate 是有效的[3H]GABA 释放剂，而释放相当量的[3H]GABA 需要毫摩尔浓度的 L-Glu 和 L-Asp。天冬氨酸（D-Asp）和谷氨酸（D-Glu）的 D-异构体能够释放[3H]GABA，但仅在高浓度（3 - 30 mM）下应用时才可以。在存在5 mM D-Asp 的情况下，L-Glu 释放[3H]GABA 的作用显著增强。在存在 D-Asp 的情况下，L-Glu 的剂量反应曲线向左移动，尽管最大释放量未改变。5 mM 的 D-Asp 仅略微增加了 quisqualate 诱导的 GABA 释放，并且它没有增加 kainate 诱导的 GABA 释放。最后，低浓度的 L-Asp 被 D-Asp 增强，但较高浓度的 L-Asp（3 - 10 mM）被该试剂明显抑制。D-Asp 对 L-Asp 诱导的[3H]GABA 释放的这种双相作用可能解释了先前关于 D-Asp 对 L-Asp 作用的相互矛盾的报道。我们的数据表明 D-Asp 具有突触前和突触后作用位点。
