Lluch Sara, López-Fuster María José, Ventura Jacint
Departament d'Optica i Optometria, Universitat Politècnica de Catalunya, Barcelona, Spain.
Anat Rec A Discov Mol Cell Evol Biol. 2003 Jun;272(2):484-90. doi: 10.1002/ar.a.10066.
The retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length = 4.22 microm in S. araneus, 5.68 microm in S. coronatus, and 2.42 microm in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron-dense matrix and a complex system of cristae, which varied in length and array. In mammalian retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich-cone retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the cone outer segment optics.
对三种鼩鼱（普通鼩鼱、冠鼩鼱和小鼩鼱）的视网膜进行了分析。根据（以及其他特征）内节线粒体的特征，鉴定出了两种光感受器。视杆细胞的内节包含几个圆形或椭圆形的线粒体，纵向分布在椭球体内部。视锥细胞的内节有一些线粒体，我们将其归类为巨型线粒体（普通鼩鼱中最大长度为4.22微米，冠鼩鼱中为5.68微米，小鼩鼱中为2.42微米）。对冠鼩鼱连续薄切片的分析表明，这些大型细胞器出现在椭球体的顶端和中央部分。在椭球体的周边和基部区域，巨型线粒体经常伴有较小的线粒体。巨型线粒体形态不规则且密集排列，每个线粒体之间观察到胞质溶胶减少。一般来说，它们呈现出电子致密的基质和复杂的嵴系统，嵴的长度和排列各不相同。在哺乳动物视网膜中，巨型线粒体仅在树鼩（笔尾树鼩和北树鼩）的椭球体中被描述过，这两种日行性的攀鼩目动物具有富含视锥细胞的视网膜。一般而言，鼩鼱的巨型线粒体在形态上与树鼩所报道的非常相似，尤其是在视锥细胞椭球体中的排列。然而，它们在嵴的方向上有所不同。我们认为，鼩鼱的椭球体可能具有两种功能：作为受体细胞的能量来源，以及作为改善视锥细胞外节光学性能的装置。
