[3H]-DA release evoked by low pH medium and internal H+ accumulation in rat hypothalamic synaptosomes:: involvement of calcium ions
[3H]-DA release evoked by low pH medium and internal H+ accumulation in rat hypothalamic synaptosomes:: involvement of calcium ions
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DOI：
10.1016/s0197-0186(02)00211-5
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发表时间：
2003-07-01
影响因子：
4.2
通讯作者：
Martire, M
中科院分区：
文献类型：
--
作者：
Cannizzaro, C;Monastero, R;Martire, M
PH的波动通常被解释为不充分的调节或作为病理事件的结果，例如缺血，在这些事件中，pH水平发生显著下降。神经递质的释放似乎受到pH下降的显著影响。在这项研究中，我们研究了细胞外和细胞内酸化对超融合大鼠下丘脑突触体氚化多巴胺释放([H-3]-DA释放)的影响。与基础释放相比，胞外酸化，由于名义上无碳的灌流介质的外部pH降低，引起[H-3]-DA释放显著增加，表现出对钙遗漏的敏感性。用5-(N-乙基-N-异丙基)-阿米洛利(EIPA)和5-(N，N-二甲基)-阿米洛利(DMA)阻断Na+/H+交换的胞内酸化后，[H-3]-DA外流显著增加，且呈钙依赖性(无钙时抑制80%)。为了通过HI内部积累进一步促进端内酸化，使用了质子离子载体黑色。在每个剂量(10微米)下，与基础释放相比，该化合物诱导[H-3]-DA流出显著增加。当不含钙的灌流液中不含钙时，尼日利亚霉素引起的[H-3]-DA释放减少50%。加入细胞内钙离子的螯合剂BAPTA-AM后，黑素诱发的[H-3]-DA完全消失。这些数据表明[H-3]-DA的释放可以由外部pH降低引起的细胞外酸化和由于内部质子积累引起的细胞内酸化引起。触发这种胞吐过程的机制似乎依赖于钙的存在，特别是依赖于细胞内钙的增加。(C)2003爱思唯尔科学有限公司。保留所有权利。
The pH fluctuations have been often interpreted as an insufficient regulation or as a consequence of the onset of pathological events, such as ischemia, in which a significant decrease in pH levels occurs. Neurotransmitter release appears to be affected by pH drop significantly. In this study, we investigated the effect of an extracellular and an intracellular acidification on tritiated dopamine release ([H-3]-DA release), from superfused rat hypothalamic synaptosomes. When compared to basal release, extracellular acidification, due to a reduction in the external pH of the nominally carbonic-free superfusion media, provoked a significant increase in [H-3]-DA release that showed a sensitiveness to calcium omission. Intraterminal acidification, obtained blocking the Na+/H+ exchanger by 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) and 5-(N,N-dimethyl)-amiloride (DMA), induced a significant increase in [H-3]-DA outflow which occurred in a calcium-dependent manner (80% inhibition in absence of calcium from superfusion media). To further promote an intraterminal acidification through a HI inner accumulation, the proton ionophore nigericin was used. At every dose employed (10 muM), this compound induced a significant increase in [H-3]-DA outflow, compared to basal release. Nigericin-evoked [H-3]-DA release showed a 50% decrease when calcium was omitted from superfusion media. When BAPTA-AM, a chelator of intracellular calcium, was added, nigericin-evoked [H-3]-DA was completely abolished. These data indicate that [H-3]-DA release can be induced by extracellular acidification due to a lowering of external pH and by an intraterminal acidification due to an internal proton accumulation. The mechanism that can trigger this exocytotic process appears to depend on calcium presence, and in particular, on an increased intraterminal calcium availability. (C) 2003 Elsevier Science Ltd. All rights reserved.