title: Contribution of Resting Conductance, GABAA-Receptor Mediated Miniature Synaptic Currents and Neurosteroid to Chloride Homeostasis in Central Neurons.
abstract: Maintenance of a low intraneuronal Cl-concentration, [Cl-]i, is critical for inhibition in the CNS. Here, the contribution of passive, conductive Cl-flux to recovery of [Cl-]iafter a high load was analyzed in mature central neurons from rat. A novel method for quantifying the resting Cl-conductance, important for [Cl-]irecovery, was developed and the possible contribution of GABAAand 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-]irecovery was tested. [Cl-]iwas examined by gramicidin-perforated patch recordings in medial preoptic neurons. Cells were loaded with Cl-by combining GABA or glycine application with a depolarized voltage, and the time course of [Cl-]iwas followed by measurements of the Cl-equilibrium potential,as obtained from the current recorded during voltage ramps combined with GABA or glycine application. The results show that passive Cl-flux contributes significantly, in the same order of magnitude as does K+-Cl-cotransporter 2 (KCC2), to [Cl-]irecovery and that Cl-conductance accounts for ∼ 6% of the total resting conductance. A major fraction of this resting Cl-conductance is picrotoxin (PTX)-sensitive and likely due to open GABAAreceptors, but ClC-2 channels do not contribute. The results also show that when the decay of GABAAreceptor-mediated miniature postsynaptic currents (minis) is slowed by the neurosteroid allopregnanolone, such minis may significantly quicken [Cl-]irecovery, suggesting a possible steroid-regulated role for minis in the control of Cl-homeostasis.
authors.affiliation: Department of Integrative Medical Biology, Umeå University , Umeå, SE-901 87, Sweden.
authors.forename: Tushar D
authors.initials: TD
authors.lastname: Yelhekar
authors.affiliation: Department of Integrative Medical Biology, Umeå University , Umeå, SE-901 87, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Druzin
authors.affiliation: Department of Integrative Medical Biology, Umeå University , Umeå, SE-901 87, Sweden.
authors.forename: Staffan
authors.identifier: 0000-0003-1022-5097
authors.initials: S
authors.lastname: Johansson
mesh_terms: D000818:Animals; D000838:Anions / Q000378:metabolism; D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D008297:Male; D055369:Miniature Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D008959:Models, Neurological; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D011301:Preoptic Area / Q000187:drug effects / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism; D046509:Tissue Culture Techniques; D000096922:K Cl- Cotransporters
chemical_list: D000838:Anions; D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; D002712:Chlorides; D018377:Neurotransmitter Agents; D011963:Receptors, GABA-A; D027981:Symporters; D000096922:K Cl- Cotransporters
keywords: GABAA receptor; KCC2; chloride homeostasis; miniature postsynaptic current; neurosteroid; resting chloride conductance