GABA‐induced uncoupling of GABA/benzodiazepine site interactions is associated with increased phosphorylation of the GABA A receptor

The use‐dependent regulation of the GABA A receptor occurs under physiological, pathological, and pharmacological conditions. Tolerance induced by prolonged administration of benzodiazepines is associated with changes in GABA A receptor function. Chronic exposure of neurons to GABA for 48 hr induces a downregulation of the GABA A receptor number and an uncoupling of the GABA/benzodiazepine site interactions. A single brief exposure (t 1/2  = 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 GABA A receptors and provides a paradigm to study the uncoupling mechanism selectively. Here we report that uncoupling induced by a brief GABA A 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 GABA A 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 GABA A 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 GABA A receptors. The uncoupling of the GABA A receptor may represent a compensatory mechanism to control GABAergic neurotransmission under conditions in which receptors are persistently activated. © 2014 Wiley Periodicals, Inc.