Forssmann W G, Girardier L
J Cell Biol. 1970 Jan;44(1):1-19. doi: 10.1083/jcb.44.1.1.
The technique of extracellular space tracing with horseradish peroxidase is adapted for labeling the transverse tubular system (T system) in rat heart. In rat ventricular muscle the T system shows extensive branching and remarkable tortuosity. The T system can only be defined operationally, since it does not display specific morphological features throughout its entire structure. Owing to branching of the T system, a sizable proportion of the apposition between the T system and L system (or closed system) occurs at the level of longitudinal branches of the T system and is not restricted to the Z line region. The regions of apposition between the T system and L system are analyzed in rat ventricular muscle and skeletal muscle (diaphragm) and compared with the intercellular tight junctions (nexuses) of heart muscle by the use of a photometric method. The over-all thickness of the nexus is significantly smaller than that of T-L junctions in both cardiac and skeletal muscles. The thickness of the membranes of the T and L systems are not significantly different in the two muscles, but the gap between both membranes is larger in the heart. In atrial muscle the following two types of cells are found: (a) those cells with a well-developed T system in which the tubular diameter is quite uniform and the orientation predominantly longitudinal and, (b) cells with no T system, but with a well-developed L system. Atrial cells possessing a T system are richly provided with specific granules and show little micropinocytotic activity, whereas cells devoid of T system show intense micropinocytotic activity and few specific granules. The possible functional implications of these findings are discussed.
用辣根过氧化物酶进行细胞外间隙追踪的技术被应用于标记大鼠心脏的横管系统（T系统）。在大鼠心室肌中，T系统呈现出广泛的分支和显著的曲折。T系统只能通过操作来定义，因为它在整个结构中并不表现出特定的形态特征。由于T系统的分支，T系统与L系统（或封闭系统）之间相当大比例的并置发生在T系统纵向分支的水平，而不仅限于Z线区域。通过光度法分析大鼠心室肌和骨骼肌（膈肌）中T系统与L系统的并置区域，并与心肌的细胞间紧密连接（连接）进行比较。在心肌和骨骼肌中，连接的总厚度明显小于T-L连接。在这两种肌肉中，T系统和L系统膜的厚度没有显著差异，但心脏中两种膜之间的间隙更大。在心房肌中发现了以下两种类型的细胞：（a）那些T系统发育良好的细胞，其中管状直径相当均匀，方向主要是纵向的；（b）没有T系统但L系统发育良好的细胞。具有T系统的心房细胞富含特定颗粒，微胞饮活性较低，而没有T系统的细胞则表现出强烈的微胞饮活性，特定颗粒较少。讨论了这些发现可能的功能意义。
