Distinct Modulation of Spontaneous and GABA-Evoked Gating by Flurazepam Shapes Cross-Talk Between Agonist-Free and Liganded GABA(A) Receptor Activity

作者：Jatczak Sliwa Magdalena^*; Terejko Katarzyna; Brodzki Marek; Michalowski Michal A; Czyzewska Marta M; Nowicka Joanna M; Andrzejczak Anna; Srinivasan Rakenduvadhana; Mozrzymas Jerzy W^*

来源：Frontiers in Cellular Neuroscience, 2018, 12: 237.

DOI：10.3389/fncel.2018.00237

• GABA(A) receptor
• gamma-aminobutyric acid
• benzodiazepines
• spontaneous activity
• preactivation
• gating
• partial agonist

GABA(A) receptors (GABAARs) play a crucial inhibitory role in the CNS. Benzodiazepines (BDZs) are positive modulators of specific subtypes of GABAARs, but the underlying mechanism remains obscure. Early studies demonstrated the major impact of BDZs on binding and more recent investigations indicated gating, but it is unclear which transitions are affected. Moreover, the upregulation of GABAAR spontaneous activity by BDZs indicates their impact on receptor gating but the underlying mechanisms remain unknown. Herein, we investigated the effect of a BDZ (flurazepam) on the spontaneous and GABA-induced activity for wild -type (WT, uir2Y2) and mutated (at the orthosteric binding site ui F64) GABAARs. Surprisingly, in spite of the localization at the binding site, these mutations increased the spontaneous activity. Flurazepam (FLU) upregulated this activity for mutants and WT receptors to a similar extent by affecting opening/closing transitions. Spontaneous activity affected GABA-evoked currents and is manifested as an overshoot after agonist removal that depended on the modulation by BDZs. We explain the mechanism of this phenomenon as a cross -desensitization of ligandactivated and spontaneously active receptors. Moreover, due to spontaneous activity, FLU -pretreatment and co -application (agonist + FLU) protocols yielded distinct results. We provide also the first evidence that GABAAR may enter the desensitized state in the absence of GABA in a FLU -dependent manner. Based on our data and model simulations, we propose that FLU affects agonist-induced gating by modifying primarily preactivation and desensitization. We conclude that the mechanisms of modulation of spontaneous and ligand-activated GABAAR activity concerns gating but distinct transitions are affected in spontaneous and agonist-evoked activity.

• 出版日期2018-8-28