Davis E C
Department of Anatomy, McGill University, Montreal, Quebec, Canada.
Lab Invest. 1993 Jan;68(1):89-99.
The structural and functional intigration of smooth muscle cells and elastic laminae in the aortic media is not well established. Detailed information concerning normal ultrastructural features of the aortic media will provide a better understanding of the medial changes that occur in vascular diseases such as hypertension and aortic aneurysms.
The ultrastructural development and organization of connections between smooth muscle cells and elastic laminae in the mouse aortic media were studied by light and electron microscopy.
Early in development, the smooth muscle cells become linked to the elastic laminae by bundles of microfibrils. These microfibrils become progressively infiltrated with elastin so as to form extensions of elastin from the elastic laminae in the adult media. Each elastin extension spans obliquely from the elastic lamina to the surface of the smooth muscle cell where it attaches in a region of membrane occupied by an intracellular membrane-associated dense plaque. On the cytoplasmic face of the plaque, a contractile filament bundle penetrates and anchors in an orientation similar to that of the extracellular elastin extension. The contractile filament bundle traverses the cell obliquely and anchors in a dense plaque on the opposite side of the cell that is in turn linked to the next elastic lamina by another elastin extension. The extracellular elastin extensions and the intracellular contractile filament bundles thus form a "contractile-elastic unit," a continuous line of structures that links adjacent elastic laminae. The oblique orientation of the contractile-elastic units reverses direction in successive smooth muscle cell layers in a herringbone-like pattern. Thus, tension transmitted to one elastic lamina by the smooth muscle cells on either side results in a uniform force exerted on the elastic lamina in one circumferential direction, that on the adjacent elastic laminae being in the opposite direction.
Results from this study demonstrate the presence of smooth muscle cell to elastic lamina connections that form early in development as contractile-elastic units; basic units of aortic medial ultrastructure. The overall organization of the contractile-elastic units within the aortic media is proposed to provide a means for coordinating contractile and elastic tensions in response to mechanical stresses imposed on the vessel wall.
主动脉中膜平滑肌细胞与弹性膜的结构和功能整合尚未完全明确。有关主动脉中膜正常超微结构特征的详细信息，将有助于更好地理解诸如高血压和主动脉瘤等血管疾病中发生的中膜变化。
通过光学显微镜和电子显微镜研究小鼠主动脉中膜平滑肌细胞与弹性膜之间连接的超微结构发育及组织情况。
在发育早期，平滑肌细胞通过微原纤维束与弹性膜相连。这些微原纤维逐渐被弹性蛋白浸润，从而在成年中膜形成从弹性膜延伸出的弹性蛋白延伸物。每个弹性蛋白延伸物从弹性膜斜向跨越至平滑肌细胞表面，并附着于由细胞内膜相关致密斑占据的膜区域。在致密斑的细胞质面，一束收缩细丝以与细胞外弹性蛋白延伸物相似的方向穿入并锚定。收缩细丝束斜向穿过细胞，并锚定在细胞另一侧的致密斑上，该致密斑又通过另一个弹性蛋白延伸物与下一个弹性膜相连。细胞外弹性蛋白延伸物和细胞内收缩细丝束因此形成一个“收缩 - 弹性单元”，这是连接相邻弹性膜的连续结构线。收缩 - 弹性单元的倾斜方向在连续的平滑肌细胞层中呈人字形模式反向。因此，两侧平滑肌细胞传递至一个弹性膜的张力会在一个圆周方向上对弹性膜施加均匀的力，而相邻弹性膜上的力方向相反。
本研究结果表明，在发育早期存在作为收缩 - 弹性单元形成的平滑肌细胞与弹性膜连接，这是主动脉中膜超微结构的基本单元。主动脉中膜内收缩 - 弹性单元的整体组织结构被认为是一种在应对施加于血管壁的机械应力时协调收缩和弹性张力的方式。
