Ionic mechanisms of spontaneous GABAergic events in rat hippocampal slices exposed to 4-aminopyridine
Ionic mechanisms of spontaneous GABAergic events in rat hippocampal slices exposed to 4-aminopyridine
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DOI：
10.1152/jn.1997.78.5.2582
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发表时间：
1997-11-01
影响因子：
2.5
通讯作者：
Kaila, K
中科院分区：
文献类型：
--
作者：
Lamsa, K;Kaila, K
用离子选择性(H+和K+)微电极技术和常规细胞内外记录技术，研究了4-氨基吡啶(4-AP，50-100µM)对大鼠海马片自发GABA能事件(SGE)传播的离子机制。所有实验均在离子型谷氨酸受体拮抗剂[10 mU M 6-硝基-7-磺酸基苯并喹恶啉-2，3-二酮(NBQX)和40 mU M DL-2-氨基-5-膦戊酸(AP5)]存在下进行。SGE由场电位负向变化和CA1区放射层细胞外K+([K+](0))和细胞外pH(pH(0))的碱性瞬变(0.01-0.08个单位)时间上的一致增加(0.7+/-0.3 mm；平均值+/-SE)组成。同时细胞内记录显示锥体细胞呈现三相超极化-去极化-晚期超极化反应。应用戊巴比妥钠可使SSE间期由平均35个缩短至接近S的20个，并缩短了刺激诱发传播事件的不应期。伴随而来的是[K+](0)场电位响应的幅度和pH(0)的移动以及锥体细胞响应的去极化阶段。γ-氨基丁酸-A(GABA(A))受体拮抗剂印防己毒素(PiTX；100 mU M)可完全阻断SGES。在名义上没有CO_2/HCO_3~-的情况下，锥体细胞响应的负向场势和去极化相的幅度以及与SGE相关的离子位移被强烈地抑制。事件间期增加了5倍，短于2-3分钟的刺激不能诱发传播性的SSE。暴露于碳酸酐酶抑制剂苯乙酰胺(BA；10mU M)或乙氧基唑胺(Eza；50mU M)可完全阻断碱性pH(0)的瞬变，并将它们转变为酸转移。膜透性差的BA对SGE的其他成分没有明显的影响，但Eza的作用与无CO_2/HCO_3的培养液相似。加入GABA(A)受体可能意味着弱酸性阴离子，甲酸盐(20 MM)重新建立了最初被暴露在无CO2/HCO3介质中抑制的SGE。在类似浓度的GABA(A)受体-阴离子丙酸盐存在的情况下，没有观察到SGE。与HCO3驱动的SGE相关的碱性瞬变不同，那些由甲酸盐支持的SGE不会被BA阻止。结果表明，小苏打携带的内向电流是产生SGES所必需的，GABA(A)受体介导的GABA(A)受体介导的GABA能中间神经元之间的兴奋性偶联本质上依赖于细胞内小苏打的可用性。
Ion-selective(H+ and K+)microelectrode techniques as well as conventional extra- and intracellular recordings were used to study the ionic mechanisms of propagating spontaneous GABAergic events (SGEs) in rat hippocampal slices exposed to 4-aminopyridine (4-AP, 50-100 mu M). All experiments were made in the presence of antagonists of ionotropic glutamate receptors [10 mu M 6-nitro-7-sulphamoyl-benzoquinoxaline-2, 3-dione (NBQX) and 40 mu M DL-2-amino-5-phosphonopentanoic acid (AP5)]. The SGEs were composed of a negative-going change in field potential with a temporally coincident increase (0.7 +/- 0.3 mM; mean +/- SE) in extracellular K+ ([K+](0)) and an alkaline transient (0.01 - 0.08 units) in extracellular pH (pH(0)) in stratum radiatum of the area CA1. Simultaneous intracellular recordings showed a triphasic hyperpolarization-depolarization-late hyperpolarization response in pyramidal cells. Application of pentobarbital sodium (PB, 100 mu M) decreased the interval between SGEs from a mean value of 35 to similar to 20 s and shortened the period of refractoriness of stimulus-evoked propagating events. This was accompanied by an increase in the amplitude of the field potential response of the [K+](0) and the pH(0) shifts and of the depolarizing phase of the pyramidal-cell response. The SGEs were completely blocked by the gamma-aminobutyric acid-A (GABA(A)) receptor antagonist, picrotoxin (PiTX; 100 mu M). The amplitudes of the negative-going field potential and of the depolarizing phase of the pyramidal-cell response as well as the ionic shifts associated with SGEs were strongly suppressed in the nominal absence of CO2/HCO3-. There was a five-fold increase in the interevent interval, and propagating SGEs could not be evoked by stimuli given at intervals shorter than similar to 2-3 min. Exposure to inhibitors of carbonic anhydrase, benzolamide (BA; 10 mu M) or ethoxyzolamide (EZA; 50 mu M) fully blocked the alkaline pH(0) transients and turned them into acid shifts. The poorly membrane-permeant BA had no discernible effect on the other components of the SGEs, but application of EZA had effects reminiscent to those of CO2/HCO3--free medium. Addition of the GABA(A) receptor-permeant weak-acid anion, formate (20 mM) reestablished the SGEs that were first suppressed by exposure to the CO2/HCO3--free medium. No SGEs were seen in the presence of a similar concentration of the GABA(A) receptor-impermeant anion propionate. Unlike the alkaline transients associated with HCO3--driven SGEs, those supported by formate were not blocked by BA. The present data suggest that an inward current carried by bicarbonate is necessary for the generation of SGEs and that the GABA(A) receptor-mediated excitatory coupling among GABAergic interneurons is essentially dependent on the availability of intracellular bicarbonate.