Wilson S P, Kirshner N
J Biol Chem. 1983 Apr 25;258(8):4994-5000.
The effects of the steroid glycoside digitonin on cultured bovine adrenal chromaffin cells were studied as a way to gain access to the intracellular sites of calcium action in stimulus-secretion coupling. Chromaffin cells treated with digitonin secreted catecholamines by an exocytotic mechanism when exposed to free calcium concentrations of greater than 1 microM. At free calcium concentrations of less than 100 microM, an apparently saturable release of catecholamines was observed with a half-maximal effect (EC50) of 3-4 microM. Catecholamine release at these low calcium concentrations was limited to 10-15% of the cellular content, was partially dependent on the presence of MgATP, and was inhibited by magnesium (EC50 = 6 mM). At calcium concentrations between 0.1 and 10 mM, a second, apparently saturable component of catecholamine release from digitonin-treated chromaffin cells was observed (EC50 = 0.3 mM). This release at the higher calcium concentrations was unaffected by the addition of MgATP, magnesium, antipsychotic drugs known to bind and inactivate calmodulin, or calcium channel blockers, but was temperature-dependent and was inhibited by N-ethylmaleimide (EC50 = 140 microM). Strontium and manganese can also evoke catecholamine secretion from digitonin-treated chromaffin cells. The results suggest that digitonin will be a useful preparation in elucidating the molecular mechanisms of the secretory process.
研究了甾体糖苷洋地黄皂苷对培养的牛肾上腺嗜铬细胞的作用，以此作为了解刺激-分泌偶联中钙作用的细胞内位点的一种方法。用洋地黄皂苷处理的嗜铬细胞在暴露于大于1微摩尔的游离钙浓度时，通过胞吐机制分泌儿茶酚胺。在游离钙浓度低于100微摩尔时，观察到儿茶酚胺的明显饱和释放，半数最大效应（EC50）为3 - 4微摩尔。在这些低钙浓度下，儿茶酚胺释放量限于细胞含量的10 - 15%，部分依赖于MgATP的存在，并受到镁的抑制（EC50 = 6毫摩尔）。在钙浓度介于0.1和10毫摩尔之间时，观察到洋地黄皂苷处理的嗜铬细胞释放儿茶酚胺的第二个明显饱和成分（EC50 = 0.3毫摩尔）。在较高钙浓度下的这种释放不受添加MgATP、镁、已知能结合并使钙调蛋白失活的抗精神病药物或钙通道阻滞剂的影响，但依赖于温度，并受到N - 乙基马来酰亚胺的抑制（EC50 = 140微摩尔）。锶和锰也能引起洋地黄皂苷处理的嗜铬细胞分泌儿茶酚胺。结果表明，洋地黄皂苷将是阐明分泌过程分子机制的一种有用制剂。
