Segawa A, Loffredo F, Puxeddu R, Yamashina S, Testa Riva F, Riva A
Department of Anatomy, School of Medicine, Kitasato University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228, Japan.
Cell Tissue Res. 1998 Feb;291(2):325-36. doi: 10.1007/s004410051002.
The luminal membrane of salivary acinar cells creates a specialized cell surface area that accepts exocytosis and undergoes dynamic changes during secretion. These changes were visualized three-dimensionally from both the inside and outside of the cell in human parotid and submandibular glands, by application of in vitro secretory stimulation and then of OsO4 maceration to remove cytoplasmic organelles by varying degrees. In control glands treated without secretagogues, the luminal surface of serous acinar cells bore well-developed microvilli with only an occasional incidence of exocytotic profiles. Following treatment with the beta-adrenergic agonist, isoproterenol, considerable shortening and loss of microvilli occurred along the luminal membrane where, on its cytoplasmic side, many protuberances of sizes similar to or smaller than those of single secretory granules (approximately 1 micron in diameter) appeared. The cytoplasmic surface of these protuberances exhibited small vesicles (approximately 100-150 nm in diameter) that, by transmission electron microscopy, were shown to be coated pits or vesicles present on or around the exocytosed granule membranes. Treatment of tissues with the muscarinic agonist carbachol also caused a decrease of microvilli and the appearance of protrusions at the luminal membrane. However, unlike isoproterenol treatment, many of these protrusions were devoid of small pits or vesicles and were much larger than a single secretory granule. These results indicate that (1) secretory stimulation causes the dynamic transformation of microvilli at the luminal membrane, where granule docking and membrane fusion take place, and (2) after fusion, the exocytosed membranes are processed differently, by coated pit/vesicle mediated or non-mediated mechanisms, according to the autonomic receptor control.
唾液腺泡细胞的管腔膜形成了一个特殊的细胞表面积，它接受胞吐作用，并在分泌过程中经历动态变化。通过体外分泌刺激，然后应用四氧化锇浸渍以不同程度去除细胞质细胞器，从人腮腺和颌下腺细胞的内部和外部对这些变化进行了三维可视化。在未经促分泌剂处理的对照腺体中，浆液性腺泡细胞的管腔表面有发育良好的微绒毛，偶尔有胞吐轮廓。用β-肾上腺素能激动剂异丙肾上腺素处理后，管腔膜上的微绒毛明显缩短并减少，在其细胞质一侧出现许多大小与单个分泌颗粒相似或更小（直径约1微米）的突起。这些突起的细胞质表面有小泡（直径约100 - 150纳米），通过透射电子显微镜显示，这些小泡是存在于胞吐颗粒膜上或其周围的包被小窝或小泡。用毒蕈碱激动剂卡巴胆碱处理组织也会导致微绒毛减少，并在管腔膜处出现突起。然而，与异丙肾上腺素处理不同的是，这些突起中的许多没有小窝或小泡，而且比单个分泌颗粒大得多。这些结果表明：（1）分泌刺激导致管腔膜上微绒毛的动态转变，颗粒对接和膜融合在此发生；（2）融合后，根据自主受体控制，胞吐后的膜通过包被小窝/小泡介导或非介导机制进行不同的处理。
