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Disrupted Cl − homeostasis contributes to reductions in the inhibitory efficacy of diazepam during hyperexcited states
Author(s) -
Deeb Tarek Z.,
Nakamura Yasuko,
Frost Greg D.,
Davies Paul A.,
Moss Stephen J.
Publication year - 2013
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/ejn.12241
Subject(s) - gabaa receptor , glutamate receptor , inhibitory postsynaptic potential , chemistry , diazepam , pharmacology , cotransporter , propofol , receptor , gaba receptor , biophysics , neuroscience , biology , biochemistry , organic chemistry , sodium
The K + ‐ Cl − cotransporter type 2 is the major Cl − extrusion mechanism in most adult neurons. This process in turn leads to Cl − influx upon activation of γ‐aminobutyric acid type A ( GABA A ) receptors and the canonical hyperpolarising inhibitory postsynaptic potential. Several neurological disorders are treated with drugs that target and enhance GABA A receptor signaling, including the commonly used benzodiazepine diazepam and the anesthetic propofol. Some of these disorders are also associated with deficits in GABA A signaling and become less sensitive to therapeutic drugs that target GABA A receptors. To date, it is unknown if alterations in the neuronal Cl − gradient affect the efficacies of diazepam and propofol. We therefore used the in vitro model of glutamate‐induced hyperexcitability to test if alterations in the Cl − gradient affect the efficacy of GABA A modulators. We exclusively utilised the gramicidin perforated‐patch‐clamp configuration to preserve the endogenous Cl − gradient in rat neurons. Brief exposure to glutamate reduced the inhibitory efficacy of diazepam within 5 min, which was caused by the collapse of the Cl − gradient, and not due to reductions in GABA A receptor number. Unlike diazepam, propofol retained its efficacy by shunting the membrane conductance despite the glutamate‐induced appearance of depolarising GABA A ‐mediated currents. Similarly, pharmacological inhibition of K + ‐ Cl − cotransporter type 2 by furosemide disrupted Cl − homeostasis and reduced the efficacy of diazepam but not propofol. Collectively our results suggest that pathological hyperexcitable conditions could cause the rapid accumulation of intracellular Cl − and the appearance of depolarising GABA A ‐mediated currents that would decrease the efficacy of diazepam.