Phorbol esters potentiate rapid dopamine release from median eminence and striatal synaptosomes.
Phorbol esters potentiate rapid dopamine release from median eminence and striatal synaptosomes.
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DOI：
10.1210/endo-122-6-2699
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发表时间：
1988-06
期刊：
影响因子：
4.8
通讯作者：
C. Shu;M. Selmanoff
中科院分区：
文献类型：
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作者：
C. Shu;M. Selmanoff
在本研究中，我们研究了佛波酯增强钙依赖性去极化诱导释放氚标记的多巴胺（[3 H]DA）从正中隆起和纹状体突触体的能力。佛波酯增强[3 H]DA释放的浓度依赖性的方式在这两种多巴胺能神经末梢，并与一系列的效力类似的刺激蛋白激酶C（PKC）的活性在其他细胞系统中的报告。去极化1、3、5和10秒后，12-O-十四酰基佛波醇-13-乙酸酯（TPA; 10（-7）M）可增加诱发的[3 H]DA释放。TPA的作用被PKC抑制剂鞘氨醇所抑制。TPA增强高K+、藜芦碱或Ca 2+离子载体A23187诱发的[3 H]DA释放。发现佛波酯增强是去极化依赖性的，因为它存在于30-75 mM，但不存在于5-20 mM外部K+。在0.01-3 mM之间研究的所有外部Ca 2+浓度下均观察到增强作用。然而，在没有外部游离Ca 2+的情况下（即用0.1 mM EGTA），佛波醇效应不存在。这些数据表明，突触体内Ca 2+浓度的增加是必要的[3 H]DA释放佛波醇酯的增强发生。TPA和Ca 2+离子载体A23187的组合没有显示在一些其他系统中观察到的显著协同作用，即最大释放没有恢复。这表明，在多巴胺能神经末梢，PKC的激活具有调节，而不是介导，释放的影响。最近，我们已经表明，高泌乳素血症刺激[3 H]DA释放正中隆起突触体的外部Ca 2+的非依赖性机制，这可能涉及PKC途径。然而，在目前的工作中，我们发现，TPA和PRL对诱发[3 H]DA释放的影响是加性的，这表明涉及两个独立的机制。正中隆起和纹状体突触体对钙离子载体的敏感性有显著差异。A23187的浓度需要支持显着的[3 H]DA释放的正中隆起突触体是3倍以上，在纹状体突触体。这表明这两种多巴胺能神经末梢在钙稳态过程中存在一些差异，例如较高的静息纹状体Ca 2+浓度。这些数据支持以下假设：PKC激活增强突触体内刺激-分泌偶联机制，黑质纹状体和结节漏斗多巴胺能神经末梢以类似方式受到佛波酯的影响。
In the present study, we investigated the ability of phorbol esters to potentiate Ca2+-dependent depolarization-induced release of tritium-labeled dopamine ([3H]DA) from median eminence and striatal synaptosomes. Phorbol esters potentiated [3H]DA release in a concentration-dependent manner in both kinds of dopaminergic nerve terminals and with a potency series similar to that reported for stimulation of protein kinase-C (PKC) activity in other cell systems. Evoked [3H]DA release was increased by 12-O-tetradecanoylphorbol-13-acetate (TPA; 10(-7) M) after 1, 3, 5, and 10 sec of depolarization. The effect of TPA was suppressed by sphingosine, a PKC inhibitor. TPA enhanced [3H]DA release evoked by high K+, veratridine or the Ca2+ ionophore A23187. Phorbol ester potentiation was found to be depolarization dependent, as it was present from 30-75 mM, but not at 5-20 mM external K+. Potentiation was seen at all external Ca2+ concentrations studied between 0.01-3 mM. However, in the absence of external free Ca2+ (i.e. with 0.1 mM EGTA), the phorbol effect was not present. These data indicate that an increase in intrasynaptosomal Ca2+ concentration is necessary for the enhancement of [3H]DA release by phorbol esters to occur. The combination of TPA and the Ca2+ ionophore A23187 does not show the marked synergism observed in some other systems, that is maximal release was not reinstated. This suggests that in dopaminergic nerve terminals, activation of PKC has a modulatory, rather than a mediating, effect on release. Recently, we have shown that hyperprolactinemia stimulated [3H]DA release from median eminence synaptosomes by an external Ca2+-independent mechanism which might involve the PKC pathway. However, in the present work we found that the TPA and PRL effects on evoked [3H]DA release were additive, suggesting that two independent mechanisms are involved. A marked difference in the sensitivity of median eminence and striatal synaptosomes to calcium ionophore was discovered. The concentration of A23187 required to support significant [3H]DA release from median eminence synaptosomes was 3-fold greater than that in striatal synaptosomes. This suggests that some difference in calcium homeostatic processes exists, such as a higher resting striatal Ca2+ concentration, in these two kinds of dopaminergic nerve terminals. These data support the hypothesis that PKC activation potentiates the intrasynaptosomal stimulus-secretion coupling mechanism(s) and that nigrostriatal and tuberoinfundibular dopaminergic nerve terminals are affected by phorbol esters in a similar manner.