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

我们使用完整的和带皮的制剂研究了调节心肌收缩的分子机制。我们用注射到雪貂乳头肌表面细胞内的水飞蓟素来测量钙瞬变和张力。肌肉长度从Lmax减少到88%Lmax时，随着张力降低，细胞内钙浓度(Extra-Ca)一过性增加。长度缩短前归一化的胞外钙到胞内钙浓度在低钙溶液中增加，在高钙浓度下降低。BAY K 8644可降低正常化的Extra-Ca。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，从而增加了肌钙蛋白C的钙亲和力，导致了较小的归一化额外钙。我们还使用Triton X-100处理的皮肤制剂测量了PCA-张力关系，并观察到该关系随肌肉长度的变化。在较长的肌肉长度时，PCA-张力关系左移(长度效应)。在较高浓度的氢离子和磷酸盐存在下，钙的响应性降低，但长度效应增强。因此，交叉桥的附着是心肌肌钙蛋白C钙亲和力随长度变化的关键因素。

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.