Waschek J A, Pruss R M, Siegel R E, Eiden L E, Bader M F, Aunis D
Ann N Y Acad Sci. 1987;493:308-23. doi: 10.1111/j.1749-6632.1987.tb27215.x.
Enkephalins, vasoactive intestinal polypeptide, and chromogranin A are all contained in the secretory vesicles of chromaffin cells in culture, and are all released from this compartment by secretagogues in a calcium-dependent way. The biosynthesis of each of these peptides, however, is under quite independent regulation. The synthesis and secretion of enkephalin is tightly coupled to acetylcholine and elevated potassium stimulation by calcium influx. Once calcium enters the cell, calcium acts at pharmacologically distinct sites to elicit secretion and enhanced biosynthesis of Metenkephalin. This is demonstrated by the calcium-independent stimulation of enkephalin secretion by 1 mM barium, in contrast to the dependence on extracellular calcium of barium-stimulated biosynthesis of this peptide. The synthesis and secretion of VIP is also coupled to acetylcholine and elevated potassium stimulation by calcium influx. Treatment with barium demonstrates that calcium acts at distinct sites to stimulate secretion and biosynthesis of this peptide; however induction of VIP by barium and veratridine shows greater sensitivity to the calcium channel blocker methoxyverapamil (D600) than does the induction of Met-enkephalin by these agents. These differences in D600 sensitivity may be due to differences in calcium metabolism or voltage-dependent calcium channels in enkephalin-producing and VIP-inducible subpopulations of chromaffin cells. Chromogranin A levels are essentially unaffected by any of the agents which increase enkephalin and VIP levels, although it is secreted in parallel with enkephalins and catecholamines from chromaffin cells in response to secretagogues. We suggest that peptide hormones such as VIP and enkephalins are regulated by calcium-dependent stimulus-secretion-synthesis coupling in the chromaffin cell. Cyclic AMP is a positive regulator of enkephalin and VIP biosynthesis, but does not affect acute release of these peptides. The cAMP/protein kinase A system may be a distal mediator of peptide biosynthesis stimulated by secretagogues. Alternatively, cAMP may be involved in early developmental establishment of phenotype or long-term regulation of peptide biosynthesis by other hormones or neurotransmitters. Chromogranin A may represent a class of intravesicular, soluble proteins that are expressed constitutively by the chromaffin cell in the presence or absence of positive regulators of other systems. The biosynthesis of chromogranin A may be coupled to the production or assembly of the secretory vesicle itself.
脑啡肽、血管活性肠肽和嗜铬粒蛋白A都存在于培养的嗜铬细胞的分泌小泡中，并且都能被促分泌剂以钙依赖的方式从这个区室释放出来。然而，这些肽各自的生物合成受到相当独立的调节。脑啡肽的合成和分泌与乙酰胆碱以及通过钙内流引起的钾浓度升高紧密相关。一旦钙进入细胞，钙会作用于药理学上不同的位点，以引发甲硫脑啡肽的分泌和生物合成增强。1 mM钡对脑啡肽分泌的刺激不依赖于钙，这与该肽钡刺激的生物合成依赖于细胞外钙形成对比，从而证明了这一点。血管活性肠肽的合成和分泌也与乙酰胆碱以及通过钙内流引起的钾浓度升高相关。用钡处理表明，钙作用于不同的位点来刺激该肽的分泌和生物合成；然而，钡和藜芦碱对血管活性肠肽的诱导比对这些药剂诱导甲硫脑啡肽对钙通道阻滞剂甲氧基维拉帕米（D600）更为敏感。D600敏感性的这些差异可能是由于嗜铬细胞中产生脑啡肽和可诱导血管活性肠肽的亚群中钙代谢或电压依赖性钙通道的差异所致。嗜铬粒蛋白A的水平基本上不受任何增加脑啡肽和血管活性肠肽水平的药剂的影响，尽管它与嗜铬细胞中的脑啡肽和儿茶酚胺一起响应促分泌剂而分泌。我们认为，血管活性肠肽和脑啡肽等肽类激素在嗜铬细胞中受钙依赖的刺激 - 分泌 - 合成偶联调节。环磷酸腺苷是脑啡肽和血管活性肠肽生物合成的正调节剂，但不影响这些肽的急性释放。环磷酸腺苷/蛋白激酶A系统可能是促分泌剂刺激肽生物合成的远端介质。或者，环磷酸腺苷可能参与表型的早期发育建立或其他激素或神经递质对肽生物合成的长期调节。嗜铬粒蛋白A可能代表一类囊泡内可溶性蛋白质，无论其他系统的正调节剂是否存在，嗜铬细胞都能组成性表达。嗜铬粒蛋白A的生物合成可能与分泌小泡本身的产生或组装相关。
