Stevenson S, Rothery S, Cullen M J, Severs N J
Imperial College School of Medicine, National Heart and Lung Institute, London, England.
Circ Res. 1997 Feb;80(2):269-80. doi: 10.1161/01.res.80.2.269.
Dystrophin is a key component of the subsarcolemmal skeleton of muscle cells, and lack of dystrophin is the direct cause of Duchenne muscular dystrophy. In skeletal muscle, dystrophin is reported to be localized specifically at costameres, transversely oriented riblike subsarcolemmal plaques that mechanically couple the contractile apparatus to the extracellular matrix. Costameres are characteristically rich in vinculin and are prominent in cardiac as well as skeletal muscle. To define the precise spatial relationship between dystrophin in relation to the costamere in cardiac muscle, we applied high-resolution single- and double-immunolabeling techniques, under a range of preparative conditions, with visualization of vinculin (as a costamere marker) and dystrophin by confocal microscopy and by the freeze-fracture cytochemical technique, fracture label. Immunoconfocal visualization revealed dystrophin as a continuous uniform layer at the cytoplasmic surface of the peripheral plasma membrane of the rat cardiac myocyte at both costameric and noncostameric regions. The pattern of labeling was reproducible with three different antibodies and was independent of time and antibody concentration. Platinum/carbon replicas and thin sections of fracture-label specimens permitted high-resolution visualization of the distribution of dystrophin in plane views of the freeze-fractured plasma membrane and in relation to the sarcomeric banding patterns of the underlying myofibrils. These results confirmed no preferential association of dystrophin with costameres or with any region of the sarcomeres of underlying myofibrils in rat cardiac tissue. We conclude that in contrast to skeletal muscle, dystrophin in cardiac muscle is not exclusively a component of the costamere.
肌营养不良蛋白是肌肉细胞肌膜下骨架的关键组成部分，缺乏肌营养不良蛋白是杜氏肌营养不良症的直接病因。在骨骼肌中，据报道肌营养不良蛋白特异性定位于肌小节，即横向排列的肋状肌膜下斑块，它将收缩装置与细胞外基质机械连接起来。肌小节的特征是富含纽蛋白，在心肌和骨骼肌中都很突出。为了确定心肌中肌营养不良蛋白与肌小节之间的精确空间关系，我们在一系列制备条件下应用了高分辨率单免疫标记和双免疫标记技术，通过共聚焦显微镜和冷冻断裂细胞化学技术（断裂标记）观察纽蛋白（作为肌小节标记物）和肌营养不良蛋白。免疫共聚焦观察显示，在大鼠心肌细胞外周质膜的细胞质表面，肌小节和非肌小节区域的肌营养不良蛋白均呈连续均匀层状分布。用三种不同抗体标记的模式具有可重复性，且与时间和抗体浓度无关。铂/碳复制品和断裂标记标本的薄片能够在冷冻断裂质膜的平面视图中以及与下层肌原纤维的肌节带模式相关的情况下，对肌营养不良蛋白的分布进行高分辨率观察。这些结果证实，在大鼠心脏组织中，肌营养不良蛋白与肌小节或下层肌原纤维肌节的任何区域均无优先关联。我们得出结论：与骨骼肌不同，心肌中的肌营养不良蛋白并非仅仅是肌小节的组成部分。
