Romei Cristina, Sabolla Chiara, Raiteri Luca
Department of Pharmacy, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy.
Department of Pharmacy, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy; Center of Excellence for Biomedical Research, University of Genoa, Genoa, Italy; National Institute of Neuroscience, Genoa, Italy.
Neurochem Int. 2014 Jun;72:1-9. doi: 10.1016/j.neuint.2014.04.003. Epub 2014 Apr 13.
GABA release provoked by ion dysregulations typical of some neuropathological conditions was analyzed in purified cerebellar synaptosomes pre-labeled with [(3)H]GABA and exposed in superfusion to KCl, 4-aminopyridine (4-AP) or veratridine. The overflows caused by relatively low concentrations of the releasers were almost totally external Ca(2+)-dependent. Higher concentrations of KCl or veratridine, but not 4-AP, involved also external Ca(2+)-independent mechanisms. The GABA overflows evoked by veratridine and, less so, the overflow evoked by high K(+), occurred in part by reversal of the GAT1 transporter. None of the depolarizing agents activated store-operated or transient receptor potential or L-type Ca(2+) channels. Only the overflow caused by 4-AP occurred in part by N- and P/Q-type voltage-sensitive calcium channel-dependent exocytosis. Significant portions of the external Ca(2+)-dependent overflows evoked by the three releasers involved reversal of plasmalemmal Na(+)/Ca(2+) exchangers. The overflows evoked by high K(+) or veratridine, but not by 4-AP were evoked by Ca(2+) originated through mitochondrial Na(+)/Ca(2+) exchangers. Ca(2+)-induced Ca(2+) release mediated by inositoltrisphosphate receptors participated exclusively in the GABA release stimulated by high KCl which also occurred in a modest portion through anion channels. Important differences could be observed between the release mechanisms of GABA here described and those previously reported for glycine, in spite of the abundant vesicular co-localization of the two transmitters in cerebellar interneurons.
在预先用[³H]GABA标记的纯化小脑突触体中，分析了某些神经病理状态典型的离子失调所引发的GABA释放情况，这些突触体在超灌流条件下暴露于氯化钾、4-氨基吡啶（4-AP）或藜芦碱。相对低浓度释放剂所引起的溢出几乎完全依赖细胞外钙离子。较高浓度的氯化钾或藜芦碱，但不是4-AP，还涉及细胞外钙离子非依赖机制。藜芦碱诱发的GABA溢出，以及程度稍轻的高钾诱发的溢出，部分是通过GAT1转运体的逆转发生的。没有一种去极化剂激活储存-操作性或瞬时受体电位或L型钙离子通道。只有4-AP引起的溢出部分是通过N型和P/Q型电压敏感性钙通道依赖性胞吐作用发生的。三种释放剂诱发的细胞外钙离子依赖性溢出的很大一部分涉及质膜钠/钙交换体的逆转。高钾或藜芦碱诱发的溢出，但不是4-AP诱发的溢出，是由通过线粒体钠/钙交换体产生的钙离子诱发的。由肌醇三磷酸受体介导的钙诱导钙释放仅参与高氯化钾刺激的GABA释放，这也有一小部分是通过阴离子通道发生的。尽管这两种递质在小脑中间神经元中大量共定位，但在这里描述的GABA释放机制与先前报道的甘氨酸释放机制之间可以观察到重要差异。
