@article {YelhekarENEURO.0019-17.2017, author = {Tushar D. Yelhekar and Michael Druzin and Staffan Johansson}, title = {Contribution of Resting Conductance, GABAA-Receptor Mediated Miniature Synaptic Currents and Neurosteroid to Chloride Homeostasis in Central Neurons }, volume = {4}, number = {2}, elocation-id = {ENEURO.0019-17.2017}, year = {2017}, doi = {10.1523/ENEURO.0019-17.2017}, publisher = {Society for Neuroscience}, abstract = {Maintenance of a low intraneuronal Cl{\textendash} concentration, [Cl{\textendash}]i, is critical for inhibition in the CNS. Here, the contribution of passive, conductive Cl{\textendash} flux to recovery of [Cl{\textendash}]i after a high load was analyzed in mature central neurons from rat. A novel method for quantifying the resting Cl{\textendash} conductance, important for [Cl{\textendash}]i recovery, was developed and the possible contribution of GABAA and glycine receptors and of ClC-2 channels to this conductance was analyzed. The hypothesis that spontaneous, action potential-independent release of GABA is important for [Cl{\textendash}]i recovery was tested. [Cl{\textendash}]i was examined by gramicidin-perforated patch recordings in medial preoptic neurons. Cells were loaded with Cl{\textendash} by combining GABA or glycine application with a depolarized voltage, and the time course of [Cl{\textendash}]i was followed by measurements of the Cl{\textendash} equilibrium potential, as obtained from the current recorded during voltage ramps combined with GABA or glycine application. The results show that passive Cl{\textendash} flux contributes significantly, in the same order of magnitude as does K+-Cl{\textendash} cotransporter 2 (KCC2), to [Cl{\textendash}]i recovery and that Cl{\textendash} conductance accounts for \~{} 6\% of the total resting conductance. A major fraction of this resting Cl{\textendash} conductance is picrotoxin (PTX)-sensitive and likely due to open GABAA receptors, but ClC-2 channels do not contribute. The results also show that when the decay of GABAA receptor-mediated miniature postsynaptic currents (minis) is slowed by the neurosteroid allopregnanolone, such minis may significantly quicken [Cl{\textendash}]i recovery, suggesting a possible steroid-regulated role for minis in the control of Cl{\textendash} homeostasis.}, URL = {https://www.eneuro.org/content/4/2/ENEURO.0019-17.2017}, eprint = {https://www.eneuro.org/content/4/2/ENEURO.0019-17.2017.full.pdf}, journal = {eNeuro} }