Kostin S, Scholz D, Shimada T, Maeno Y, Mollnau H, Hein S, Schaper J
Department of Experimental Cardiology, Max-Planck Institute, Benekestrasse 2, D-61231 Bad Nauheim, Germany.
Cell Tissue Res. 1998 Dec;294(3):449-60. doi: 10.1007/s004410051196.
The transverse tubule system of the cardiomyocyte remains undeformed despite the extreme forces it undergoes during the contraction-relaxation cycle, but the morphological basis for its stability remains unclear. Therefore, we have investigated the architecture and subcellular protein scaffold of the cardiac T-tubules and compared it with that of the costameres and of the free sarcolemma. Tissue samples from normal rat and monkey hearts, and left ventricular tissue from normal and cardiomyopathic human hearts obtained at transplantation surgery were investigated using immunocytochemistry and confocal microscopy and by electron microscopy. In addition, we used a re-differentiation model of isolated, cultured adult rat cardiomyocytes. The cell membrane of the cardiac T-tubules was found to contain the cell-matrix focal adhesion molecules (FAMs) vinculin, talin, the alpha5beta1 integrin and the membrane-associated proteins (MAPs) dystrophin and spectrin. FAMs and MAPs were localized in the T-tubular membrane in a similar pattern: in longitudinally oriented myocytes as transverse punctate lines at the Z-level; in transversally cut myocytes a radial tubular network was found to extend throughout the interior of the cell. Immunolabeling for basement membrane components including collagen IV, fibronectin and laminin showed a colocalization with FAMs and MAPs parallel to the transverse T-tubules. The costameres of the sarcolemma showed a protein composition resembling that of the T-tubules but the intervening segments of free sarcolemma showed absence of FAMs and presence of MAPs. For the first time, we demonstrate the existence and protein composition of the T-tubular scaffold in the human heart. Furthermore, we show that cardiomyocytes from human failing hearts have less abundant but more dilated T-tubules than do experimental animals. These results indicate that the cardiac T-tubular system contains a subcellular scaffold closely resembling that of the costameres. It consists of FAMs, MAPs and basal lamina proteins that confer structural integrity to the cardiac T-tubular membrane during contraction/relaxation cycles.
心肌细胞的横小管系统在收缩 - 舒张周期中承受极端力量时仍保持不变形，但其稳定性的形态学基础尚不清楚。因此，我们研究了心脏横小管的结构和亚细胞蛋白支架，并将其与肌小节和游离肌膜的进行比较。使用免疫细胞化学、共聚焦显微镜和电子显微镜对正常大鼠和猴心脏的组织样本，以及移植手术中获取的正常和心肌病患者心脏的左心室组织进行了研究。此外，我们使用了分离培养的成年大鼠心肌细胞的再分化模型。发现心脏横小管的细胞膜含有细胞 - 基质黏着斑分子（FAMs）纽蛋白、踝蛋白、α5β1整合素以及膜相关蛋白（MAPs）肌营养不良蛋白和血影蛋白。FAMs和MAPs以类似的模式定位在横小管膜中：在纵向排列的心肌细胞中，在Z水平呈横向点状线；在横向切割的心肌细胞中，发现一个放射状管状网络贯穿细胞内部。对包括IV型胶原、纤连蛋白和层粘连蛋白在内的基底膜成分的免疫标记显示，它们与FAMs和MAPs在平行于横向横小管的位置共定位。肌膜的肌小节显示出与横小管相似的蛋白质组成，但游离肌膜的中间段显示不存在FAMs且存在MAPs。我们首次证明了人类心脏中横小管支架的存在及其蛋白质组成。此外，我们表明，与实验动物相比，人类衰竭心脏的心肌细胞横小管数量较少但扩张更明显。这些结果表明，心脏横小管系统包含一个与肌小节非常相似的亚细胞支架。它由FAMs、MAPs和基底膜蛋白组成，在收缩/舒张周期中赋予心脏横小管膜结构完整性。
