Titin determines the Frank-Starling relation in early diastole
Titin determines the Frank-Starling relation in early diastole
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DOI：
10.1085/jgp.20028652
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发表时间：
2003-02-01
影响因子：
3.8
通讯作者：
Sawyer, DB
中科院分区：
文献类型：
--
作者：
Helmes, M;Lim, CC;Sawyer, DB
肌凝蛋白是一种巨大的蛋白质，横跨一半的肌节，在肌节伸长和压缩过程中分别负责心肌肌丝的被动和恢复力。此外，在舒张期到收缩期的过渡过程中，肌小节的长度依赖性激活与titin有关。本研究的目的是研究titin在舒张早期（当肌细胞缩短至松弛长度以下）发生的长度依赖性失活中的作用。我们开发了一种新的体外实验来评估肌细胞恢复力（RF） 1，测量triton渗透性，卸载大鼠心肌细胞在严格诱导的肌节长度（SL）收缩后的反冲速度。我们比较了严谨诱导的SL缩短和钙诱导的（pCa）收缩。RF-SL关系呈线性相关，SL-pCa曲线呈特征s型曲线。titin的作用是通过用低浓度的胰蛋白酶处理肌细胞来确定的，我们使用质谱分析显示，胰蛋白酶选择性地降解titin。胰蛋白酶处理降低了肌细胞RF， RF- sl关系的斜率下降，这伴随着SL-pCa曲线的向下和左移，表明肌丝对钙的敏感化。此外，胰蛋白酶消化没有改变钙活化后SL与纤维间距（以细胞宽度评估）之间的关系。这些数据表明，当肌节缩短到松弛长度以下时，基于titin的恢复力作用于肌丝脱敏。此外，与长SLs的长度依赖性激活相反，长度依赖性失活不依赖于丝间间距。这项研究首次证明了在舒张期早期长度依赖性失活中，以titin为基础的恢复力的重要性。
Titin, a giant protein spanning half the sarcomere, is responsible for passive and restoring forces in cardiac myofilaments during sarcomere elongation and compression, respectively. In addition, titin has been implicated in the length-dependent activation that occurs in the stretched sarcomere, during the transition from diastole to systole. The purpose of this study was to investigate the role of titin in the length-dependent deactivation that occurs during early diastole, when the myocyte is shortened below slack length. We developed a novel in vitro assay to assess myocyte restoring force (RF) 1 measuring the velocity of recoil in Triton-permeabilized, unloaded rat cardiomyocytes after rigor-induced sarcomere length (SL) contractions. We compared rigor-induced SL shortening to that following calcium-induced (pCa) contractions. The RF-SL relationship was linearly correlated, and the SL-pCa curve displayed a characteristic sigmoidal curve. The role of titin was defined by treating myocytes with a low concentration of trypsin, which we show selectively degrades titin using mass spectroscopic analysis. Trypsin treatment reduced myocyte RF as shown by a decrease in the slope of the RF-SL relationship, and this was accompanied by a downward and leftward shift of the SL-pCa curve, indicative of sensitization of the myofilaments to calcium. In addition, trypsin digestion did not alter the relationship between SL and interfilament spacing (assessed by cell width) after calcium activation. These data suggest that as the sarcomere shortens below slack length, titin-based restoring forces act to desensitize the myofilaments. Furthermore, in contrast to length-dependent activation at long SLs, length-dependent deactivation does not depend on interfilament spacing. This study demonstrates for the first time the importance of titin-based restoring force in length-dependent deactivation during the early phase of diastole.