EVIDENCE OF AN EXOCYTOTIC-LIKE RELEASE OF [H-3] 5-HYDROXYTRYPTAMINE INDUCED BY D-FENFLURAMINE IN RAT HIPPOCAMPAL SYNAPTOSOMES
EVIDENCE OF AN EXOCYTOTIC-LIKE RELEASE OF [H-3] 5-HYDROXYTRYPTAMINE INDUCED BY D-FENFLURAMINE IN RAT HIPPOCAMPAL SYNAPTOSOMES
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DOI：
10.1016/0014-2999(93)90499-8
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发表时间：
1993-07-06
影响因子：
5
通讯作者：
MENNINI, T
中科院分区：
文献类型：
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作者：
GOBBI, M;FRITTOLI, E;MENNINI, T
使用体外模型研究了 d-芬氟拉明的单胺释放活性，该模型由预载有 H-3-神经递质的突触体组成，并在接触 d-芬氟拉明 3 分钟之前在灌流装置中进行了广泛清洗。使用该模型，药物诱导的释放是真实的，并且不会与药物再摄取的抑制相混淆。 d-芬氟拉明 (0.5 muM) 只诱导海马突触体释放 [H-3]5-羟色胺 ([H-3]5-HT)，而 10 muM 也诱导预载 [H-3] 去甲肾上腺素的海马突触体或预载 [H-3] 多巴胺的纹状体突触体释放一些溢出，尽管溢出量远低于释放5-HTergic 突触体。然后，我们重点关注 0.5 muM d-芬氟拉明诱导的 [H-3]5-HT 释放，此前已证明其具有 Ca2+ 依赖性。本研究与其他实验方案也证实了相同的发现，表明需要细胞外 Ca2+ 离子。通过测量大鼠海马突触体的 [H-3]5-HT 摄取，我们证实 5-HT 摄取载体的功能或其与 d-芬氟拉明的相互作用不需要 Ca2+-离子。 1 μM 尼群地平（阻断 L 型 Ca2+ 通道）不会改变 d-芬氟拉明诱导的 [H-3]5-HT 释放，但 0.5 μM omega-芋螺毒素（阻断 N 型 Ca2+ 通道）会略微降低 (20%)。它还被 0.5 μM 可乐定（与 α2-肾上腺素能异质受体相互作用）和 10 nM 破伤风毒素（已知会影响包括 5-HT 在内的不同神经递质的胞吐作用）抑制。这些化合物对去极化（即 15 mM K+）诱导的 [H-3]5-HT 的 Ca2+ 依赖性胞吐释放具有非常相似的作用。这些数据表明，d-芬氟拉明在载体介导的进入突触体后，诱导细胞外 Ca2+ 流入，引发 5-HT 的胞吐样释放。
The monoamine releasing activity of d-fenfluramine was investigated with an in vitro model consisting of synaptosomes preloaded with the H-3-neurotransmitter and extensively washed in a superfusion apparatus before a 3-min exposure to d-fenfluramine. With this model, the drug-induced release is real and is not confused by inhibition of reuptake by the drug. d-Fenfluramine (0.5 muM) induced only [H-3]5-hydroxytryptamine ([H-3]5-HT) release from hippocampal synaptosomes whereas 10 muM also induced some overflow from hippocampal synaptosomes preloaded with [H-3]noradrenaline or from striatal synaptosomes preloaded with [H-3]dopamine, although the overflow was much lower than from 5-HTergic synaptosomes. We then focused on the [H-3]5-HT release induced by 0.5 muM d-fenfluramine, which was previously shown to be Ca2+ dependent. The same finding was confirmed in the present study with other experimental protocols, indicating the requirement for extracellular Ca2+ ions. By measuring [H-3]5-HT uptake into rat hippocampal synaptosomes we confirmed that Ca2+-ions are not required for the function of the 5-HT uptake carrier or for its interaction with d-fenfluramine. d-Fenfluramine-induced [H-3]5-HT release was not altered by 1 muM nitrendipine (blocking the L-type Ca2+channels) but was slightly decreased (20%) by 0.5 muM omega-conotoxin (blocking the N-type Ca2+ channels). It was also inhibited by 0.5 muM clonidine, interacting with alpha2-adrenergic heteroreceptors, and by 10 nM tetanus toxin, known to affect the exocytosis of different neurotransmitters including 5-HT. These compounds had very similar effects on the Ca2+-dependent, exocytotic release of [H-3]5-HT induced by depolarization, i.e. by 15 mM K+. These data suggest that d-fenfluramine, after its carrier-mediated entry into the synaptosomes, induces an influx of extracellular Ca2+, triggering an exocytotic-like release of 5-HT.