Burgoyne Thomas, Muhamad Farina, Luther Pradeep K
Molecular Medicine Section, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, London, UK.
Cardiovasc Res. 2008 Mar 1;77(4):707-12. doi: 10.1093/cvr/cvm117. Epub 2008 Jan 4.
An intriguing difference between vertebrate skeletal and cardiac muscles is that the lengths of the thin filaments are constant in the former but variable in the latter. The thick filaments have constant lengths in both types of muscles. The contractile behaviour of a muscle is affected by the lengths of both types of filaments as the tension generated during contraction depends on the amount of filament overlap. To understand the behaviour of cardiac muscle, it is important to know the distribution of the thin filament lengths. The previous detailed analysis by Robinson and Winegrad used serial transverse sections to determine the lengths of the thin filaments. However, the precision, set by the 100 nm section thickness, was low. Here, we have used electron tomography to produce 3D images of rat and mouse cardiac muscles in which we can actually see individual thin filaments up to the free ends and see that these free ends have variable locations. For comparison, we also measure the thin filament lengths in skeletal muscle (frog sartorius).
Cardiac papillary muscles were obtained from a rat (Sprague-Dawley) and a mouse (C57/B6). Skeletal muscle (sartorius) was obtained from a frog (Rana pipiens). Longitudinal sections (100 nm thick) were used to produce tilt series and tomograms from which the thin filament paths were traced. Cardiac papillary muscle thin filaments in rat and mouse range from 0.94 to 1.10 microm, with a mean length of 1.04 microm and standard deviation of 0.03 microm. For frog sartorius muscle, the thin filament length was 0.94 microm with standard deviation of 0.01 microm.
Electron tomography of cardiac and skeletal muscles allows direct visualization and high precision measurement of the lengths of thin filaments.
脊椎动物的骨骼肌和心肌之间存在一个有趣的差异，即细肌丝的长度在前者中是恒定的，而在后者中是可变的。两种类型的肌肉中粗肌丝的长度都是恒定的。肌肉的收缩行为受两种肌丝长度的影响，因为收缩过程中产生的张力取决于肌丝重叠的量。为了了解心肌的行为，了解细肌丝长度的分布很重要。罗宾逊和温格拉德之前的详细分析使用连续横切面来确定细肌丝的长度。然而，由100纳米切片厚度所设定的精度较低。在这里，我们使用电子断层扫描技术生成大鼠和小鼠心肌的三维图像，在这些图像中我们实际上可以看到单个细肌丝直至其自由端，并发现这些自由端的位置是可变的。为了进行比较，我们还测量了骨骼肌（青蛙缝匠肌）中的细肌丝长度。
从一只大鼠（斯普拉格 - 道利大鼠）和一只小鼠（C57/B6小鼠）获取心脏乳头肌。从一只青蛙（豹蛙）获取骨骼肌（缝匠肌）。使用纵向切片（100纳米厚）来生成倾斜系列和断层图像，从中追踪细肌丝的路径。大鼠和小鼠心脏乳头肌的细肌丝长度范围为0.94至1.10微米，平均长度为1.04微米，标准差为0.03微米。对于青蛙缝匠肌，细肌丝长度为0.94微米，标准差为0.01微米。
心肌和骨骼肌的电子断层扫描技术能够直接可视化并高精度测量细肌丝的长度。
