MECHANISMS OF SLOWED MYOCARDIAL RELAXATION

描述(改编自申请人的摘要)：总体目标 这项研究是为了确定钙的作用和跨桥动力学。 在4种生理状态下心肌松弛减慢 与缺血/再灌注有关：缺氧、复氧、酸中毒和 钙增敏剂的变力刺激。其基本原理是 松弛受损的机制尚未解决。以前的研究 强调减缓胞浆[钙]下降的重要性 ([CA]c)松弛减慢。然而，[Ca]c的下降并不能很好地关联 松弛，因为[Ca]c通过几个 中间的台阶。松弛是由状态的下降决定的 对[Ca]c的反应和跨桥动力学的激活，但这些 在与缺血/再灌流相关的情况下没有测量到。这个 拟议的实验将确定[Ca]c的相对贡献， 钙激活和跨桥动力学以减缓松弛。这个 实验策略将是使用分离的大鼠心脏小梁。[CA]c 将用INDO-1荧光进行测量。将确定CA激活 通过应用短暂的肌肉拉伸来分离所有的横桥并减少 力归零；钙激活(跨桥连接和连接的能力 发展部队)将根据部队重新发展的初始速度进行评估 在伸展之后。钙激活的时间进程将由 在抽搐过程中的不同时间进行伸展。跨桥 动力学将从最大缩短速度进行评估。这个 具体目标是检验4个假说：1.缺氧时，[Ca]c减慢 下降导致钙激活下降，从而导致缓慢的松弛。 2.复氧可延缓钙活性下降，延缓跨桥 运动学导致放松的速度变慢。3.有了缺氧，酸中毒的原因就会减缓 [Ca]c下降，减缓钙激活下降，并松弛。4. 肌丝钙增敏剂左西孟丹不能减缓钙激活的下降， 和放松。

DESCRIPTION (adapted from the applicant's abstract): The overall goal of this research is to determine the roles of calcium and cross-bridge kinetics in the slowing of myocardial relaxation during 4 physiological conditions relevant to ischemia/reperfusion: hypoxia, reoxygenation, acidosis and inotropic stimulation with Ca-sensitizers. The rationale is that the mechanisms of impaired relaxation are unresolved. Previous studies emphasized the importance of slowing of the decline of cytosolic [calcium] ([Ca]c) in slowed relaxation. However [Ca]c decline does not correlate well with relaxation because [Ca]c influences force indirectly through several intervening steps. Relaxation is determined by the decline in the state of activation in response to [Ca]c and by cross-bridge kinetics, but these have not been measured during conditions relevant to ischemia/reperfusion. The proposed experiments will determine the relative contributions of [Ca]c, Ca-activation, and cross-bridge kinetics to slowed relaxation. The experimental strategy will be to use isolated rat cardiac trabeculae. [Ca]c will be measured with indo-1 fluorescence. Ca-activation will be determined by applying a brief muscle stretch to detach all cross-bridges and reduce force to zero; Ca-activation (the ability of cross-bridges to attach and develop force) will be assessed from the initial rate of force redevelopment after the stretch. The time course of Ca-activation will be defined by applying stretches at different times during twitches. Cross-bridge kinetics will be assessed from the maximum shortening velocity. The specific aim will be to test 4 hypotheses: 1. With hypoxia, slowed [Ca]c decline causes slowed Ca-activation decline which causes slowed relaxation. 2. With reoxygenation, slowed Ca-activation decline and slowed cross-bridge kinetics causes slowed relaxation. 3. With hypoxia, acidosis causes slowed [Ca]c decline, slowed Ca-activation decline, and relaxation. 4. The myofilament Ca-sensitizer Levosimendan does not slow Ca-activation decline, and relaxation.