Institute of Physiology, University Medical Center Mainz, Johannes Gutenberg University, Duesbergweg 6, 55128, Mainz, Germany.
Research Center of Neurology, Volokolamskoyeshosse, 80, Moscow, Russia, 125367.
Sci Rep. 2020 Oct 27;10(1):18399. doi: 10.1038/s41598-020-75382-1.
Activation of GABA receptors causes in immature neurons a functionally relevant decrease in the intracellular Cl concentration ([Cl]), a process termed ionic plasticity. Amount and duration of ionic plasticity depends on kinetic properties of [Cl] homeostasis. In order to characterize the capacity of Cl accumulation and to quantify the effect of persistent GABAergic activity on [Cl], we performed gramicidin-perforated patch-clamp recordings from CA3 pyramidal neurons of immature (postnatal day 4-7) rat hippocampal slices. These experiments revealed that inhibition of NKCC1 decreased [Cl] toward passive distribution with a time constant of 381 s. In contrast, active Cl accumulation occurred with a time constant of 155 s, corresponding to a rate of 15.4 µM/s. Inhibition of phasic GABAergic activity had no significant effect on steady state [Cl]. Inhibition of tonic GABAergic currents induced a significant [Cl] increase by 1.6 mM, while activation of tonic extrasynaptic GABA receptors with THIP significantly reduced [Cl]. Simulations of neuronal [Cl] homeostasis supported the observation, that basal levels of synaptic GABAergic activation do not affect [Cl]. In summary, these results indicate that active Cl-uptake in immature hippocampal neurons is sufficient to maintain stable [Cl] at basal levels of phasic and to some extent also to compensate tonic GABAergic activity.
GABA 受体的激活会导致未成熟神经元细胞内氯离子浓度（[Cl]）发生功能相关的下降，这一过程被称为离子可塑性。离子可塑性的程度和持续时间取决于氯离子稳态的动力学特性。为了描述氯离子积累的能力，并量化持续的 GABA 能活性对 [Cl]的影响，我们对发育不成熟（出生后第 4-7 天）的大鼠海马脑片 CA3 锥体神经元进行了 gramicidin 穿孔膜片钳记录。这些实验表明，NKCC1 的抑制会使 [Cl]向被动分布方向减少，时间常数为 381s。相比之下，主动氯离子积累的时间常数为 155s，对应于 15.4µM/s 的速率。相比较短暂的 GABA 能活性的抑制，氯离子稳态并无显著变化。持续的 GABA 能电流的抑制会引起氯离子浓度显著增加 1.6mM，而用 THIP 激活持续的突触外 GABA 受体则会显著降低 [Cl]。神经元氯离子稳态的模拟结果支持了以下观察结果，即基础水平的突触 GABA 能激活不会影响 [Cl]。总之，这些结果表明，在发育不成熟的海马神经元中，氯离子的主动摄取足以维持基础水平的氯离子稳定，在一定程度上也足以补偿持续的 GABA 能活性。
