gamma-Aminobutyric acid (GABA)- and barbiturate-mediated 36Cl- uptake in rat brain synaptoneurosomes: evidence for rapid desensitization of the GABA receptor-coupled chloride ion channel.
gamma-Aminobutyric acid (GABA)- and barbiturate-mediated 36Cl- uptake in rat brain synaptoneurosomes: evidence for rapid desensitization of the GABA receptor-coupled chloride ion channel.
复制标题
大鼠脑突触神经小体中γ-氨基丁酸（GABA）和巴比妥酸盐介导的 36Cl- 摄取：GABA 受体偶联氯离子通道快速脱敏的证据。
作者：
R. D. Schwartz;P. Suzdak;S. Paul
使用体外方法测量脑囊泡（突触神经小体）中氯（Cl-）渗透性，研究了γ-氨基丁酸（GABA）受体偶联氯离子通道的“脱敏”。蝇蕈醇（一种 GABA 激动剂）以浓度依赖性方式刺激大鼠大脑皮质突触神经体中 36Cl- 的摄取 (EC50 7.3 +/- 0.5 microM)，而戊巴比妥以双相方式刺激 36Cl- 摄取，如钟形浓度-反应关系所示，在 500 microM 时具有最大反应 (EC50 271 +/- 17微米）。较高浓度的戊巴比妥导致 36Cl- 吸收的刺激逐渐减弱，并阻断蝇蕈醇刺激的 36Cl- 吸收。较低浓度的戊巴比妥 (100-200 µM) 与蝇蕈醇一起添加时，会产生刺激 36Cl- 吸收的累加效应，而更低（阈值以下）浓度的戊巴比妥 (50 µM) 会增强蝇蕈醇刺激的 36Cl- 吸收。将突触神经体连续暴露于蝇蕈醇（50 µM）或戊巴比妥（500 µM）后（长达 20 分钟），36Cl-摄取反应减弱至新的稳态水平，t1/2 分别约为 6 秒和 30 秒。对这些激动剂的反应减少取决于浓度和暴露时间。在长时间（20 分钟）孵育后，未观察到阈下浓度的戊巴比妥增强蝇蕈醇刺激的 36 Cl 吸收的能力下降。在实验中观察到蝇蕈醇和戊巴比妥之间的“异源脱敏”，其中在用另一种预处理后将蝇蕈醇或戊巴比妥添加到囊泡中。这些发现表明，GABA 受体/Cl-离子通道的“脱敏”可能涉及 GABA 和巴比妥酸盐识别位点或共同的效应元件（例如离子载体本身）。
"Desensitization" of the gamma-aminobutyric acid (GABA) receptor-coupled chloride ion channel was studied using an in vitro method for measuring chloride (Cl-) permeability in brain vesicles (synaptoneurosomes). Muscimol, a GABA agonist, stimulated 36Cl- uptake in rat cerebral cortical synaptoneurosomes in a concentration-dependent manner (EC50 7.3 +/- 0.5 microM), whereas pentobarbital stimulated 36Cl- uptake in a biphasic manner, indicated by a bell-shaped concentration-response relationship, with a maximal response at 500 microM (EC50 271 +/- 17 microM). Higher concentrations of pentobarbital led to progressively smaller stimulation of 36Cl- uptake and blocked muscimol-stimulated 36Cl- uptake. Lower concentrations of pentobarbital (100-200 microM), when added with muscimol, produced an additive effect in stimulating 36Cl- uptake, whereas even lower (subthreshold) concentrations of pentobarbital (50 microM) potentiated muscimol-stimulated 36Cl- uptake. Following continuous exposure of synaptoneurosomes (up to 20 min) to muscimol (50 microM) or pentobarbital (500 microM), the 36Cl- uptake response diminished to a new steady state level with a t1/2 of approximately 6 sec and 30 sec, respectively. The decrement in response to these agonists was dependent on both concentration and length of exposure. No decrement was observed in the ability of subthreshold concentrations of pentobarbital to enhance muscimol-stimulated 36Cl- uptake following prolonged (20 min) incubation. "Heterologous desensitization" between muscimol and pentobarbital was observed in experiments where either muscimol or pentobarbital was added to the vesicles following pretreatment with the other. These findings suggest that "desensitization" of the GABA receptor/Cl- ion channel may involve both the GABA and barbiturate recognition sites or a common effector component such as the ionophore itself.