Extracellular chloride and the maintenance of spontaneous epileptiform activity in rat hippocampal slices
Extracellular chloride and the maintenance of spontaneous epileptiform activity in rat hippocampal slices
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DOI：
10.1152/jn.1999.81.1.49
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发表时间：
1999-01-01
影响因子：
2.5
通讯作者：
Schwartzkroin, PA
中科院分区：
文献类型：
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作者：
Hochman, DW;D'Ambrosio, R;Schwartzkroin, PA
先前的研究表明，速尿阻断自发性癫痫样活动，但不会减少突触传递或减少对电刺激的高兴奋场反应。我们现在验证了一个假设，即速尿的抗癫痫作用是通过阻断Na+，K+,2Cl（-）共转运体介导的，因此应该通过减少细胞外氯离子（[Cl-](o)）来模拟。在第一组实验中，海马CA1细胞体层的现场记录显示，低[Cl-](o) （7 mM）介质灌注后10-20分钟内，CA1细胞自发破裂，但10-20分钟后自发性癫痫样活动停止。CA1锥体细胞的细胞内记录显示，即使在组织灌注低[Cl-](o)培养基bbbb2小时后，膜去极化也能引起正常的动作电位放电。在第二组实验中，高[K+](o) （10 mM）、双库兰（100 μ M）或4-氨基吡啶（100 μ M）灌注切片可诱导自发破裂活动。在每种情况下，来自CA1区的记录显示，[Cl-](o)减少到21 mM可在1小时内可逆地阻断破裂。与先前使用速尿治疗的观察结果相似，低[Cl-](o)介质阻断自发的超同步放电，而不降低突触的超兴奋性（即电刺激引起的超兴奋场反应）。在第三组实验中，将切片长时间暴露于有系统变化的[Cl-](0)和[K+]（0)下，（在自发爆发停止后）会导致三种类型的事件之一：1）自发的、持久的、重复的负场电位移动(7 mM [Cl-](0)；3 mM [K+](o))；2)场电位负移5 ~ 10mv的振荡，周期为1周期/40 s (16mm [Cl-](o)；12 mM [K+](o))；3)持续20 ~ 40 s (21 mM [Cl-](o)的较短且不经常发生的负场位移；3mm [K+](o))。我们的观察表明，低[Cl-](o)对神经元同步和自发放电的影响是时间依赖性的。在呋塞米和低[Cl-](o)中也观察到类似的效果，这与呋塞米的抗癫痫作用是由药物对氯转运体的作用介导的假设相一致。最后，改变细胞外钾和氯离子的结果表明，阻断Na+， K+,2Cl（-）共转运体是这些抗癫痫作用的关键。Na+, K+,2Cl（-）共转运体通常将氯离子从细胞外空间转运到神经胶质细胞。
Previous studies showed that furosemide blocks spontaneous epileptiform activity without diminishing synaptic transmission or reducing hyperexcited field responses to electrical stimuli. We now test the hypothesis that the antiepileptic effects of furosemide are mediated through its blockade of the Na+,K+,2Cl(-) cotransporter and thus should be mimicked by a reduction of extracellular chloride ([Cl-](o)). In the first set of experiments, field recordings from the CA1 cell body layer of hippocampal slices showed that spontaneous bursting developed within 10-20 min in slices perfused with low-[Cl-](o) (7 mM) medium but that this spontaneous epileptiform activity ceased after a further 10-20 min. Intracellular recordings from CA1 pyramidal cells showed that normal action potential discharge could be elicited by membrane depolarization, even after the tissue was perfused with low-[Cl-](o) medium for >2 h. In a second set of experiments, spontaneous bursting activity was induced in slices by perfusion with high-[K+](o) (10 mM), bicuculline (100 mu M), or 4-aminopyridine (100 mu M). In each case, recordings from the CA1 region showed that reduction of [Cl-](o) to 21 mM reversibly blocked the bursting within 1 h. Similar to previous observations with furosemide treatment, low-[Cl-](o) medium blocked spontaneous hypersynchronous discharges without reducing synaptic hyperexcitability (i.e., hyperexcitable field responses evoked by electrical stimulation). In a third set of experiments, prolonged exposure (>1 h after spontaneous bursting ceased) of slices to systematically varied [Cl-](o) and [K+](o) resulted in one of three types of events: 1) spontaneous, long-lasting, and repetitive negative field potential shifts (7 mM [Cl-](o); 3 mM [K+](o)); 2) oscillations consisting of 5- to 10-mV negative shifts in the field potential, with a period of similar to 1 cycle/40 s (16 mM [Cl-](o); 12 mM [K+](o)); and 3) shorter, infrequently occurring negative field shifts lasting 20-40 s (21 mM [Cl-](o); 3 mM [K+](o)). Our observations indicate that the effects of low [Cl-](o) on neuronal synchronization and spontaneous discharge are time dependent. Similar effects were seen with furosemide and low [Cl-](o), consistent with the hypothesis that the antiepileptic effect of furosemide is mediated by the drug's effect on chloride transporters. Finally, the results of altering extracellular potassium along with chloride suggest that blockade of the Na+, K+,2Cl(-) cotransporter, which normally transports chloride from the extracellular space into glial cells, is key to these antiepileptic effects.