Department of Medical and Morphological Research, Section of Anatomy, University of Udine, Udine, Italy.
J Anat. 2010 Apr;216(4):518-24. doi: 10.1111/j.1469-7580.2009.01198.x. Epub 2010 Jan 28.
In this study we used a modified osmium maceration method for high-resolution scanning electron microscopy to study some ultrastructural details fitting the schema of piecemeal degranulation in chromaffin cells. Piecemeal degranulation refers to a particulate pattern of cell secretion that is accomplished by vesicle-mediated extracellular transport of granule-stored material. We investigated adrenal samples from control and angiotensin II-treated rats, and identified a variable proportion of smooth, 30-60-nm-diameter vesicles in the cytoplasm of chromaffin cells. A percentage of these vesicles were interspersed in the cytosol among chromaffin granules but the majority appeared to be attached to granules. Remarkably, the number of unattached cytoplasmic vesicles was greatly increased in chromaffin cells from angiotensin II-treated animals. Vesicles of the same structure and dimension were detected close to or attached to the cytoplasmic face of the plasma membrane; these, too, were increased in number in chromaffin cells from rats stimulated with angiotensin II. In specimens shaken with a rotating agitator during maceration, the cytoplasmic organelles could be partially removed and the fine structure of the vesicular interaction with the inner side of the plasma membrane emerged most clearly. A proportion of chromaffin granules showed protrusions that we interpreted as vesicular structures budding from the granular envelope. In some instances, the transection plane intersected granules with putative vesicles emerging from the surfaces. In these cases, the protrusions of budding vesicles could be observed from the internal side. This study provides high-resolution scanning electron microscopy images compatible with a vesicle-mediated degranulation mode of cell secretion in adrenal chromaffin cells. The data indicating an increase in the number of vesicles observed in chromaffin cells after stimulation with the chromaffin cell secretagogue angiotensin II suggests that this secretory process may be susceptible to fine regulation.
在这项研究中，我们使用改良的锇固定方法进行高分辨率扫描电子显微镜研究，以研究一些符合嗜铬细胞逐渐脱颗粒模式的超微结构细节。逐渐脱颗粒是指通过囊泡介导的颗粒储存物质的细胞外运输来实现的颗粒状分泌模式。我们研究了来自对照和血管紧张素 II 处理的大鼠的肾上腺样本，并在嗜铬细胞的细胞质中鉴定出具有可变比例的光滑、30-60nm 直径的囊泡。这些囊泡的一部分散布在嗜铬颗粒之间的细胞质中，但大多数似乎附着在颗粒上。值得注意的是，来自血管紧张素 II 处理的动物的嗜铬细胞中未附着的细胞质囊泡数量大大增加。具有相同结构和尺寸的囊泡在靠近或附着在质膜细胞质侧的位置被检测到；在由血管紧张素 II 刺激的大鼠的嗜铬细胞中，这些囊泡的数量也增加了。在固定过程中用旋转搅拌器摇动标本时，可以部分去除细胞质细胞器，并且囊泡与质膜内侧面的精细结构最清晰地显现出来。一部分嗜铬颗粒显示出突起，我们将其解释为从颗粒包膜出芽的囊泡结构。在某些情况下，横切面与从表面出现的推定囊泡的颗粒相交。在这些情况下，可以从内部观察到出芽囊泡的突起。这项研究提供了与肾上腺嗜铬细胞中囊泡介导的细胞分泌脱颗粒模式兼容的高分辨率扫描电子显微镜图像。表明在刺激嗜铬细胞分泌剂血管紧张素 II 后观察到的囊泡数量增加的数据表明，这种分泌过程可能容易受到精细调节。
