Effect of length and cross-bridge attachment on Ca2+ binding to cardiac troponin C.
Effect of length and cross-bridge attachment on Ca2+ binding to cardiac troponin C.
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DOI：
10.1152/ajpcell.1987.253.1.c90
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发表时间：
1987-07
期刊：
影响因子：
--
通讯作者：
P. Hofmann;F. Fuchs
中科院分区：
文献类型：
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作者：
P. Hofmann;F. Fuchs
皮肤心肌束对Ca2+的敏感性是肌节长度的函数。Ca2+敏感性随着纤维长度沿着力-长度曲线的上升肢延长而增加，并且已经提出这种现象对存在于活体心肌中的陡峭力-长度关系做出了主要贡献。为了更深入地了解Ca2+与洗涤剂提取的牛结合的Ca2+敏感性同位素测量的长度依赖背后的机制，在肌钙蛋白C是唯一主要的Ca2+结合物种的条件下制造心室肌束。实验旨在确定1)Ca2+-肌钙蛋白C亲和力是否在与力-长度曲线上升肢相对应的肌节长度范围内变化，以及2)Ca2+结合是否与长度本身或长度依赖性交叉桥附着物数量的变化相关。在严格和放松状态下测量Ca2+结合。后一种状态是通过抑制肌动蛋白-肌球蛋白与磷酸盐类似物钒酸钠的相互作用而产生的。在钒酸盐处理后，有可能在生理MgATP浓度存在和恒定的肌节长度下获得完整的Ca2+饱和曲线。结果表明，Ca2+与心肌肌钙蛋白C调控位点的结合是长度依赖的，但这种长度依赖实际上是依赖于连接的交叉桥的数量。
The sensitivity of skinned cardiac muscle bundles to Ca2+ is a function of sarcomere length. Ca2+ sensitivity is increased as fiber length is extended along the ascending limb of the force-length curve and it has been suggested that this phenomenon makes a major contribution to the steep force-length relationship that exists in living cardiac muscle. To gain greater insight into the mechanism behind the length dependence of Ca2+ sensitivity isotopic measurements of Ca2+ binding to detergent-extracted bovine, ventricular muscle bundles were made under conditions in which troponin C was the only major Ca2+ binding species. Experiments were designed to determine whether 1) Ca2+-troponin C affinity varies in the sarcomere length range corresponding to the ascending limb of the force-length curve, and 2) Ca2+ binding correlates with length per se or with changes in the number of length-dependent cross-bridge attachments. Measurements were made of Ca2+ binding in the rigor and relaxed states. The latter state was produced by suppressing actin-myosin interaction with the phosphate analogue, sodium vanadate. After vanadate treatment it is possible to obtain a complete Ca2+ saturation curve in the presence of physiological MgATP concentrations and at constant sarcomere length. The results show that the binding of Ca2+ to the regulatory site of cardiac troponin C is length dependent but this length dependence is actually a dependence on the number of attached cross bridges.