Molecular Mechanisms of Active Cross-bridge-dependent Regulation of Ca affinity of Cardiac Troponin

我们研究了调节心肌收缩的分子机制，使用完整的和剥皮的制剂。我们用注射到雪貂乳头肌浅表细胞的aequorin测量钙瞬态和张力。肌肉长度从Lmax减少到88%Lmax，随着张力的降低，细胞内钙浓度（extra-Ca）瞬间增加。长度还原前的归一化外钙到胞内钙浓度在低钙浓度的溶液中增加，在高钙浓度的溶液中减少。k8644降低了归一化外加钙。这些结果表明，细胞内钙浓度的增加增加了连接的交叉桥的数量，这增加了肌钙蛋白C的钙亲和力，导致小的标准化的额外钙。我们还使用Triton x -100处理的皮肤制剂测量了pca -张力关系，并观察了肌肉长度依赖性的关系转移。肌长较长时，pca -张力关系向左偏移（长度效应）。在较高浓度的氢离子和磷酸盐存在下，钙响应性降低，长度效应增强。因此，交叉桥的连接是心肌肌钙蛋白C钙亲和力长度依赖性变化的关键因素。

We investigated molecular mechanisms which regulate cardiac muscle contraction using intact and skinned preparations. We measured the Ca transients and tension using aequorin which was injected into superficial cells of ferret papillary muscles. A decrease in muscle length from Lmax to 88%Lmax transiently increased intracellular Ca concentration (extra-Ca) in accordance with tension reduction. The normalized extra-Ca to intracellular Ca concentration before length reduction was increased in the solution with low Ca concentration and was reduced at higher Ca concentrations. Bay K 8644 decreased the normalized extra-Ca. These results suggest that an increase in intracellular Ca concentration increases the number of attached cross-bridges and this increases the Ca affinity of troponin C, resulting in the small normalized extra-Ca. We also measured pCa-tension relation using Triton X-100-treated skinned preparations and observed the muscle length-dependent shift of the relation. pCa-tension relation was shifted to the left at longer muscle lengths (length effect). In the presence of higher concentrations of H ion and phosphate, Ca responsiveness was decreased but length effect was enhanced. Thus, attachment of the cross-bridges is a critical factor for length-dependent change in Ca affinity of cardiac troponin C.