Annaert W G, Llona I, Backer A C, Jacob W A, De Potter W P
Laboratory of Neuropharmacology and Neurobiology, University of Antwerp (UIA), Belgium.
J Neurochem. 1993 May;60(5):1746-54. doi: 10.1111/j.1471-4159.1993.tb13399.x.
"Synaptic-like microvesicles" are present in all neuroendocrine cells and cell lines. Despite their resemblance to small synaptic vesicles of the CNS, a thorough biochemical characterization is lacking. Moreover, the subcellular distribution of synaptophysin, the most abundant integral membrane protein of small synaptic vesicles, in adrenal medulla is still controversial. Using gradient centrifugation, we were able to compare the distribution of several markers for small synaptic vesicles and chromaffin granules. Synaptophysin was found at a high density (1.16 g/ml), purifying away from dopamine beta-hydroxylase and cytochrome b561. Both noradrenaline and adrenaline showed a parallel distribution with synaptophysin, suggesting their presence in synaptic-like microvesicles. Experiments in the presence of tetrabenazine did not influence the catecholamine content. Additionally, tetrabenazine binding showed a consistent shoulder in the region of synaptophysin. [3H]Noradrenaline uptake was blocked by tetrabenazine, but not by desipramine. Also chromogranin A parallels the distribution of synaptophysin; however, a localization in the Golgi cannot be ruled out. Synaptophysin was shown to undergo very fast phosphorylation, together with another triplet protein of approximately 18 kDa. In contrast, the latter showed a rather bimodal distribution coinciding with synaptophysin and dopamine beta-hydroxylase. Immunoelectron microscopy of synaptic-like microvesicle fractions showed an intense labeling for synaptophysin on 60-90-nm organelles. Whereas abundant gold labeling for cytochrome b561 was found over the entire surface of chromaffin granules, synaptophysin labeling was encountered mostly on vesicles adsorbed to granules. We conclude that catecholamines might be stored in synaptic-like microvesicles of the chromaffin cell.
“突触样微泡”存在于所有神经内分泌细胞和细胞系中。尽管它们与中枢神经系统的小突触泡相似，但缺乏全面的生化特征描述。此外，小突触泡中最丰富的整合膜蛋白——突触素在肾上腺髓质中的亚细胞分布仍存在争议。利用梯度离心法，我们能够比较几种小突触泡和嗜铬颗粒标志物的分布。发现突触素以高密度（1.16 g/ml）存在，与多巴胺β-羟化酶和细胞色素b561分离。去甲肾上腺素和肾上腺素均与突触素呈现平行分布，表明它们存在于突触样微泡中。在丁苯那嗪存在的情况下进行的实验并未影响儿茶酚胺含量。此外，丁苯那嗪结合在突触素区域呈现出一致的肩峰。[3H]去甲肾上腺素摄取被丁苯那嗪阻断，但未被地昔帕明阻断。嗜铬粒蛋白A也与突触素的分布平行；然而，不能排除其在高尔基体中的定位。已证明突触素与另一种约18 kDa的三联体蛋白一起经历非常快速的磷酸化。相比之下，后者呈现出与突触素和多巴胺β-羟化酶一致的相当双峰分布。突触样微泡组分的免疫电子显微镜检查显示，在60 - 90纳米的细胞器上突触素标记强烈。虽然在嗜铬颗粒的整个表面发现了丰富的细胞色素b561金标记，但突触素标记大多出现在吸附于颗粒的小泡上。我们得出结论，儿茶酚胺可能储存在嗜铬细胞的突触样微泡中。
