PASSIVE AND ACTIVE TENSION IN SINGLE CARDIAC MYOFIBRILS
PASSIVE AND ACTIVE TENSION IN SINGLE CARDIAC MYOFIBRILS
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DOI：
10.1016/s0006-3495(94)80538-7
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发表时间：
1994-08-01
影响因子：
3.4
通讯作者：
POLLACK, GH
中科院分区：
文献类型：
--
作者：
LINKE, WA;POPOV, VI;POLLACK, GH
从化学剥皮的兔心脏中分离出单个肌原纤维，并将其安装在先前描述的装置中（Fearn 等人，1993；Linke 等人，1993）。我们测量了被动长度-张力关系和主动等长力，两者均归一化为横截面积。肌原纤维横截面积是根据相差图像和电子显微照片测量的肌原纤维直径来计算的。肌节长度约 2.2 μm 的被动张力值与较大心肌样本中报告的值相似。因此，在生理肌节长度上负责大部分（如果不是全部）心肌被动力的元素似乎存在于肌原纤维内。超过 2.2 μm，被动张力继续上升，但不如多细胞制剂中报道的那么陡峭。显然，除了肌原纤维之外的结构在确定这些拉伸长度下被动张力的大小方面变得越来越重要。了解被动张力的肌原纤维成分使我们能够推断肌联蛋白的应力-应变关系，肌联蛋白被认为支持肌节中的被动力。肌动蛋白的弹性模量为3.5 x 10(6) dyn cm(-2)，该值与报道的弹性蛋白的值相似。肌节长度为 2.1-2.3 μm 时单个肌原纤维的最大主动等长张力为 145 +/- 35 mN/mm(2)（平均值 +/- SD；n = 15）。当考虑到这些制剂中的非肌原纤维空间量时，该值与较大心脏样本的固定端收缩中测量的值相当。然而，它比先前在类似条件下测量的单个骨骼肌原纤维的最大主动张力低约 4 倍（Bartoo 等，1993）。
Single myofibrils were isolated from chemically skinned rabbit heart and mounted in an apparatus described previously (Fearn et al., 1993; Linke et al., 1993). We measured the passive length-tension relation and active isometric force, both normalized to cross sectional area. Myofibrillar cross sectional area was calculated based on measurements of myofibril diameter from both phase-contrast images and electron micrographs. Passive tension values up to sarcomere lengths of approximately 2.2 mu m were similar to those reported in larger cardiac muscle specimens. Thus, the element responsible for most, if not all, passive force of cardiac muscle at physiological sarcomere lengths appears to reside within the myofibrils. Above 2.2 mu m, passive tension continued to rise, but not as steeply as reported in multicellular preparations. Apparently, structures other than the myofibrils become increasingly important in determining the magnitude of passive tension at these stretched lengths. Knowing the myofibrillar component of passive tension allowed us to infer the stress-strain relation of titin, the polypeptide thought to support passive force in the sarcomere. The elastic modulus of titin is 3.5 x 10(6) dyn cm(-2), a value similar to that reported for elastin. Maximum active isometric tension in the single myofibril at sarcomere lengths of 2.1-2.3 mu m was 145 +/- 35 mN/mm(2) (mean +/- SD; n = 15). This value is comparable with that measured in fixed-end contractions of larger cardiac specimens, when the amount of nonmyofibrillar space in those preparations is considered. However, it is about 4 times lower than the maximum active tension previously measured in single skeletal myofibrils under similar conditions (Bartoo et al., 1993).