Jarolimek W, Lewen A, Misgeld U
I. Physiologisches Institut der Universität Heidelberg, D-69120 Heidelberg, Germany.
J Neurosci. 1999 Jun 15;19(12):4695-704. doi: 10.1523/JNEUROSCI.19-12-04695.1999.
Efficacy of postsynaptic inhibition through GABAA receptors in the mammalian brain depends on the maintenance of a Cl- gradient for hyperpolarizing Cl- currents. We have taken advantage of the reduced complexity under which Cl- regulation can be investigated in cultured neurons as opposed to neurons in other in vitro preparations of the mammalian brain. Tightseal whole-cell recording of spontaneous GABAA receptor-mediated postsynaptic currents suggested that an outward Cl- transport reduced dendritic [Cl-]i if the somata of cells were loaded with Cl- via the patch pipette. We determined dendritic and somatic reversal potentials of Cl- currents induced by focally applied GABA to calculate [Cl-]i during variation of [K+]o and [Cl-] in the patch pipette. [Cl-]i and [K+]o were tightly coupled by a furosemide-sensitive K+-Cl- cotransport. Thermodynamic considerations excluded the significant contribution of a Na+-K+-Cl- cotransporter to the net Cl- transport. We conclude that under conditions of normal [K+]o the K+-Cl- cotransporter helps to maintain [Cl-]i at low levels, whereas under pathological conditions, under which [K+]o remains elevated because of neuronal hyperactivity, the cotransporter accumulates Cl- in neurons, thereby further enhancing neuronal excitability.
通过γ-氨基丁酸A（GABAA）受体介导的突触后抑制在哺乳动物大脑中的功效取决于维持用于超极化氯离子电流的氯离子梯度。与哺乳动物大脑的其他体外制备物中的神经元相比，我们利用了培养神经元中较低的复杂性来研究氯离子调节。对自发的GABAA受体介导的突触后电流进行全细胞膜片钳记录表明，如果通过膜片吸管将细胞的胞体加载氯离子，向外的氯离子转运可降低树突状氯离子浓度（[Cl-]i）。我们通过局部施加γ-氨基丁酸（GABA）诱导氯离子电流，测定树突状和胞体的氯离子电流反转电位，以计算在膜片吸管中改变细胞外钾离子浓度（[K+]o）和氯离子浓度时的[Cl-]i。[Cl-]i和[K+]o通过呋塞米敏感的钾离子-氯离子共转运紧密耦合。热力学考虑排除了钠离子-钾离子-氯离子共转运体对净氯离子转运的显著贡献。我们得出结论，在正常[K+]o条件下，钾离子-氯离子共转运体有助于将[Cl-]i维持在低水平，而在病理条件下，由于神经元活动亢进，[K+]o仍然升高，共转运体在神经元中积累氯离子，从而进一步增强神经元兴奋性。
