Gutiérrez María L, Ferreri María C, Farb David H, Gravielle María C
Instituto de Investigaciones Farmacológicas, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, Buenos Aires, Argentina.
J Neurosci Res. 2014 Aug;92(8):1054-61. doi: 10.1002/jnr.23387. Epub 2014 Apr 10.
The use-dependent regulation of the GABAA receptor occurs under physiological, pathological, and pharmacological conditions. Tolerance induced by prolonged administration of benzodiazepines is associated with changes in GABAA receptor function. Chronic exposure of neurons to GABA for 48 hr induces a downregulation of the GABAA receptor number and an uncoupling of the GABA/benzodiazepine site interactions. A single brief exposure ((t1/2) = 3 min) of rat neocortical neurons to the neurotransmitter initiates a process that results in uncoupling hours later (t(1/2) = 12 hr) without alterations in the number of GABAA receptors and provides a paradigm to study the uncoupling mechanism selectively. Here we report that uncoupling induced by a brief GABAA receptor activation is blocked by the coincubation with inhibitors of protein kinases A and C, indicating that the uncoupling is mediated by the activation of a phosphorylation cascade. GABA-induced uncoupling is accompanied by subunit-selective changes in the GABAA receptor mRNA levels. However, the GABA-induced downregulation of the α3 subunit mRNA level is not altered by the kinase inhibitors, suggesting that the uncoupling is the result of a posttranscriptional regulatory process. GABA exposure also produces an increase in the serine phosphorylation on the GABAA receptor γ2 subunit. Taken together, our results suggest that the GABA-induced uncoupling is mediated by a posttranscriptional mechanism involving an increase in the phosphorylation of GABAA receptors. The uncoupling of the GABAA receptor may represent a compensatory mechanism to control GABAergic neurotransmission under conditions in which receptors are persistently activated.
GABAA受体的使用依赖性调节发生在生理、病理和药理条件下。长期服用苯二氮䓬类药物所诱导的耐受性与GABAA受体功能的变化有关。神经元长期暴露于GABA 48小时会导致GABAA受体数量下调以及GABA/苯二氮䓬位点相互作用解偶联。大鼠新皮质神经元单次短暂暴露（(t1/2) = 3分钟）于神经递质会启动一个过程，该过程数小时后（t(1/2) = 12小时）导致解偶联，而GABAA受体数量无变化，并提供了一个选择性研究解偶联机制的范例。在此我们报告，短暂的GABAA受体激活所诱导的解偶联被与蛋白激酶A和C抑制剂共同孵育所阻断，这表明解偶联是由磷酸化级联反应的激活介导的。GABA诱导的解偶联伴随着GABAA受体mRNA水平的亚基选择性变化。然而，GABA诱导的α3亚基mRNA水平下调不受激酶抑制剂影响，这表明解偶联是转录后调节过程的结果。GABA暴露还会使GABAA受体γ2亚基上的丝氨酸磷酸化增加。综上所述，我们的结果表明，GABA诱导的解偶联是由一种转录后机制介导的，该机制涉及GABAA受体磷酸化增加。GABAA受体的解偶联可能代表一种在受体持续激活的条件下控制GABA能神经传递的补偿机制。
