Thick-Filament Strain and Interfilament Spacing in Passive Muscle: Effect of Titin-Based Passive Tension
Thick-Filament Strain and Interfilament Spacing in Passive Muscle: Effect of Titin-Based Passive Tension
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DOI：
10.1016/j.bpj.2011.01.059
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发表时间：
2011-03-16
影响因子：
3.4
通讯作者：
Granzier, Henk
中科院分区：
文献类型：
--
作者：
Irving, Thomas;Wu, Yiming;Granzier, Henk
我们通过同时测量被动张力和兔腰大肌被动纤维束的小角X射线衍射图，研究了基于Titin的被动张力对肌节结构的影响。我们使用拉伸-保持-释放方案，在被动应力松弛前后的保持阶段测量了不同被动张力水平下的X射线衍射图。测量是在不含和含有葡聚糖T-500的松弛溶液中进行的，以将晶格压缩到生理水平。在肌节的A带(d(1，0))和Z盘区(d(Z))测量肌丝晶格间距。粗丝主干的轴向间距由第六次肌球蛋白经向反射(M6)和第四次肌球蛋白层线峰位的平衡位置和I(1，1)/I(1，0)强度比确定。在X射线实验中测量总被动张力，并使用差示提取技术来确定胶原和Titin被动张力与肌节长度的关系。在所使用的肌节长度范围内(类似于2.2-3.4微米)，Titin占被动张力的80%。X-射线衍射结果表明，TiTiN同时压缩了A带和Z盘晶格间距，当纤维结皮后膨胀时具有粘弹性行为，而当晶格被葡聚糖还原时具有弹性行为。在存在和不存在葡聚糖的情况下，Titin还以弹性的方式增加了轴向粗丝间距M6。在被动应力松弛过程中，I(1，1)/I(1，0)和第四肌球蛋白层线上的峰位置均未发生变化。被动张力和M6测量转换为粗丝顺应性，得到的值类似于85m/N，比其他人在激活的完整肌肉的强直性张力平台期间测定的粗丝顺应性大几倍。这种差异可以用以下事实来解释：粗丝在低张力(被动肌肉)下比在高张力(强直性张力)下更顺从。讨论了我们的发现的含义。
We studied the effect of titin-based passive tension on sarcomere structure by simultaneously measuring passive tension and low-angle x-ray diffraction patterns on passive fiber bundles from rabbit skinned psoas muscle. We used a stretch-hold-release protocol with measurement of x-ray diffraction patterns at various passive tension levels during the hold phase before and after passive stress relaxation. Measurements were performed in relaxing solution without and with dextran T-500 to compress the lattice toward physiological levels. The myofilament lattice spacing was measured in the A-band (d(1,0)) and Z-disk (d(z)) regions of the sarcomere. The axial spacing of the thick-filament backbone was determined from the sixth myosin meridional reflection (M6) and the equilibrium positions of myosin heads from the fourth myosin layer line peak position and the I(1,1)/I(1,0) intensity ratio. Total passive tension was measured during the x-ray experiments, and a differential extraction technique was used to determine the relations between collagen- and titin-based passive tension and sarcomere length. Within the employed range of sarcomere lengths (similar to 2.2-3.4 mu m), titin accounted for > 80% of passive tension. X-ray results indicate that titin compresses both the A-band and Z-disk lattice spacing with viscoelastic behavior when fibers are swollen after skinning, and elastic behavior when the lattice is reduced with dextran. Titin also increases the axial thick-filament spacing, M6, in an elastic manner in both the presence and absence of dextran. No changes were detected in either I(1,1)/I(1,0) or the position of peaks on the fourth myosin layer line during passive stress relaxation. Passive tension and M6 measurements were converted to thick-filament compliance, yielding a value of similar to 85 m/N, which is several-fold larger than the thick-filament compliance determined by others during the tetanic tension plateau of activated intact muscle. This difference can be explained by the fact that thick filaments are more compliant at low tension (passive muscle) than at high tension (tetanic tension). The implications of our findings are discussed.