Vitale M L, Rodríguez Del Castillo A, Trifaró J M
Department of Pharmacology, Faculty of Medicine, University of Ottawa, Canada.
Neuroscience. 1992 Nov;51(2):463-74. doi: 10.1016/0306-4522(92)90330-5.
Nicotinic stimulation and high K+ depolarization of bovine chromaffin cells cause disassembly of cortical filamentous actin networks. Previous work from our laboratory has demonstrated that disassembly of actin filaments is Ca(2+)-dependent, precedes exocytosis and occurs in cortical areas of low cytoplasmic viscosity which are the sites of exocytosis. It has also been suggested that protein kinase C is involved in catecholamine secretion from chromaffin cells. Therefore, the possibility that protein kinase C activation might be implicated in cortical filamentous actin disassembly was investigated. Here we report that phorbol myristate acetate, a protein kinase C activator, causes cortical filamentous actin disassembly. Short-term phorbol ester treatment does not alter the morphology of chromaffin cells; however, 1 h after phorbol ester exposure an increase in cell flattening and membrane ruffling is observed. Phorbol ester-induced cortical filamentous actin disassembly is inhibited by protein kinase C activity inhibitors, is independent of extracellular Ca2+ and has a slower time course than that induced by either nicotinic receptor stimulation or K(+)-depolarization. Phorbol ester effects are likely to be mediated by activation of protein kinase C and not by any changes in intracellular Ca2+ levels, as indicated by measurements of Ca2+ transients. Pretreatment of chromaffin cells with phorbol myristate acetate increases the initial rate of nicotine-evoked catecholamine release. Nicotine-induced cortical actin filament disassembly and catecholamine secretion are partially (29-40%) inhibited by pretreatment of cells with either calphostin C, staurosporine or sphingosine. The results suggest that protein kinase C may be involved in the reorganization of the cortical actin filament network priming the cells for release by removing a barrier to secretory granule mobility. However, its role in exocytosis is modulatory but not essential.
烟碱刺激和高钾去极化可导致牛嗜铬细胞皮质丝状肌动蛋白网络解体。我们实验室之前的研究表明，肌动蛋白丝的解体是钙离子依赖性的，发生在胞吐作用之前，且发生在胞吐作用部位的低细胞质粘度的皮质区域。也有研究表明蛋白激酶C参与嗜铬细胞的儿茶酚胺分泌。因此，我们研究了蛋白激酶C激活可能与皮质丝状肌动蛋白解体有关的可能性。在此我们报告，佛波酯（一种蛋白激酶C激活剂）可导致皮质丝状肌动蛋白解体。短期佛波酯处理不会改变嗜铬细胞的形态；然而，在佛波酯暴露1小时后，可观察到细胞扁平化和膜皱襞增加。佛波酯诱导的皮质丝状肌动蛋白解体受到蛋白激酶C活性抑制剂的抑制，与细胞外钙离子无关，且其时间进程比烟碱受体刺激或钾离子去极化诱导的解体要慢。如钙离子瞬变测量所示，佛波酯的作用可能是由蛋白激酶C的激活介导的，而不是由细胞内钙离子水平的任何变化介导的。用佛波酯预处理嗜铬细胞可增加尼古丁诱发的儿茶酚胺释放的初始速率。用钙磷蛋白C、星形孢菌素或鞘氨醇预处理细胞可部分（29 - 40%）抑制尼古丁诱导的皮质肌动蛋白丝解体和儿茶酚胺分泌。结果表明，蛋白激酶C可能参与皮质肌动蛋白丝网络的重组，通过消除分泌颗粒移动的障碍使细胞为释放做好准备。然而，其在胞吐作用中的作用是调节性的而非必需的。
