Forbes M S, Mock O B, Van Niel E E
Department of Physiology, University of Virginia School of Medicine, Charlottesville 22908.
Anat Rec. 1990 Jan;226(1):57-70. doi: 10.1002/ar.1092260108.
The heart of the least shrew, Cryptotis parva Say, is an extremely active organ, capable of achieving rates of 800-1,200 beats/minute. The general features of myocardial cell ultrastructure in this insectivore are much like those of other small mammals; no single striking feature of fine structure is present to which the physiological properties of this heart might necessarily be attributed. Still there exist in these myocardial cells a number of atypical properties. These include 1) mitochondria having a wide variety of sizes and internal configurations 2) a pleiomorphic, highly ramified, small-diameter transverse-axial tubular system (TATS) 3) numerous "labyrinths," which are proliferated components of the TATS, and 4) myofibril-free regions, located both in juxtanuclear and other myoplasmic levels and populated by a concentration of TATS elements and fibrillar structures. Features (2) and (3) are also characteristic of another fast-beating heart, that of the mouse. The sinoatrial and atrioventricular nodal regions, as well as a Purkinje system, have been identified in the least shrew heart, along with sparsely distributed atrial cells whose myofibrils contain proliferated Z-band material. A feature frequently encountered in atrial working muscle cells is the occurrence of close appositions between gap junctions and tubules of sarcoplasmic reticulum; such appositions are also present in other regions of the shrew heart, as are complexes composed of gap junctions and mitochondria.
最小的鼩鼱——北美小麝鼩（Cryptotis parva Say）的心脏是一个极其活跃的器官，能够达到每分钟800 - 1200次的跳动频率。这种食虫动物心肌细胞超微结构的一般特征与其他小型哺乳动物非常相似；没有单一显著的精细结构特征可以必然地归因于该心脏的生理特性。不过，这些心肌细胞仍存在一些非典型特性。这些特性包括：1）线粒体大小和内部结构多种多样；2）一个多形的、高度分支的、小直径的横向 - 轴向管状系统（TATS）；3）众多“迷宫”，它们是TATS的增殖成分；4）无肌原纤维区域，位于核周和其他肌浆水平，由集中的TATS元件和纤维状结构组成。特征（2）和（3）也是另一个快速跳动的心脏——小鼠心脏的特征。在北美小麝鼩的心脏中已鉴定出窦房结和房室结区域以及浦肯野系统，同时还发现了稀疏分布的心房细胞，其肌原纤维含有增殖的Z带物质。心房工作肌细胞中经常遇到的一个特征是间隙连接与肌浆网小管之间紧密相邻；这种相邻关系在鼩鼱心脏的其他区域也存在，间隙连接和线粒体组成的复合体也是如此。
