CHARACTERIZATION OF RADIAL FORCE AND RADIAL STIFFNESS IN CA2+-ACTIVATED SKINNED FIBERS OF THE RABBIT PSOAS MUSCLE
CHARACTERIZATION OF RADIAL FORCE AND RADIAL STIFFNESS IN CA2+-ACTIVATED SKINNED FIBERS OF THE RABBIT PSOAS MUSCLE
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DOI：
10.1113/jphysiol.1991.sp018774
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发表时间：
1991-09-01
影响因子：
5.5
通讯作者：
YU, LC
中科院分区：
文献类型：
--
作者：
BRENNER, B;YU, LC
1.当钙离子以170 mm的离子强度激活化学剥离的肌纤维时，肌纤维之间的距离随力的增加而减小，这表明交叉桥不仅可以在轴向产生力，而且在径向也可以产生力。用X射线衍射法研究了活化后的兔腰大肌单层纤维的径向力和径向刚度。考察了葡聚糖T500对渗透压变化的响应，相当于径向作用力。在相同离子强度为170 mM的情况下，计算了附着的交叉桥产生的径向力，近似地认为在松弛的肌肉中附着了可以忽略的一小部分交叉桥。主动径向力是晶格间距的一种轻微的非线性函数，在34 nm处达到零。当晶格间距大于34 nm时，径向力为压缩，小于34 nm时，径向力为膨胀。另一方面，研究发现，应用葡聚糖T500对主动轴向力的影响要小得多。当葡聚糖T500浓度为4%时，主动轴向力增加4%，达到平台期，8%葡聚糖T500.4浓度时，轴向力下降10%。在非渗透压下，活化纤维的径向力为400pN(单根粗丝)-1。这与轴向力的量级相同。在7Pn(粗丝)-1(0.1 nm)-1.5时，径向刚度也与轴向刚度相当。完全活化纤维的径向弹性与纤维的刚性有很大的不同。在30pN(粗丝)-1(0.1 nm)-1处，僵直的纤维表现出的径向硬度大约高出5倍，径向力达到零的点是38 nm。在激活状态下，径向力达到零的点与钙离子的激活程度无关，也就是说，在力产生状态下，与肌动蛋白连接的交叉桥的数量无关。我们认为零力点等同于弹簧的平衡点，是交叉桥径向弹性的固有性质。结果表明，活跃式和刚构式跨桥在径向上表现出弹簧性。此外，径向弹性的平衡点似乎取决于跨桥的生理状态。讨论了径向弹性的大小和不同平衡点的意义。
1. When chemically skinned muscle fibres are activated by Ca2+ at an ionic strength of 170 mM, the spacing between the filaments has been shown to decrease with increasing force, suggesting that the cross-bridges can generate force not only in the axial but also in the radial direction. In the present study, radial force and radial stiffness of activated single skinned rabbit psoas fibres were studied by X-ray diffraction. The responses of the lattice spacing to changes in osmotic pressure by application of dextran T500, which is equivalent to force applied in the radial direction, was examined. The radial force generated by the attached cross-bridges was calculated, with the approximation that a negligible fraction of cross-bridges was attached in the relaxed muscle at the same ionic strength of 170 mM.2. The active radial force was found to be a slightly non-linear function of lattice spacing, reaching zero at 34 nm. The radial force was compressive at lattice spacing greater than 34 nm and expansive at less than 34 nm.3. The active axial force, on the other hand, was found to be much less affected by the application of dextran T500. Active axial force increased by 4% to a plateau at 4% dextran T500 and then decreased by 10% at 8% dextran T500.4. While not under osmotic pressure, the radial force of the activated fibre was determined to be 400 pN (single thick filament)-1. This is of the same order of magnitude as the axial force. The radial stiffness was also comparable to the axial stiffness at 7 pN (thick filament)-1 (0.1 nm)-1.5. The radial elasticity of the fully activated fibre differs significantly from that of the fiber in rigor. The radial stiffness exhibited by fibres in rigor was approximately five times higher, at 30 pN (thick filament)-1 (0.1 nm)-1 and the point where the radial force reached zero was 38 nm.6. In the activated state, the point at which radial force reaches zero is independent of the level of Ca2+ activation, i.e. independent of the number of cross-bridges attached to actin in the force-generating state. We suggest that the zero-force point is equivalent to the equilibrium point of a spring and is an intrinsic property of the radial elasticity of the cross-bridge.7. It is concluded that activated and rigor cross-bridges exhibit a spring-like property in the radial direction. Furthermore, the equilibrium point of the radial elasticity appears to depend on the physiological state of the cross-bridges. The significance of the large magnitude of radial elasticity and of the different equilibrium points is discussed.