Janssen P M, de Tombe P P
Section on Cardiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1045, USA.
Am J Physiol. 1997 Apr;272(4 Pt 2):H1892-7. doi: 10.1152/ajpheart.1997.272.4.H1892.
Isolated cardiac muscle preparations suffer from damaged-end compliance that allows for substantial shortening of central sarcomeres during contractions in which the overall length of muscle is kept constant. The impact of uncontrolled sarcomere shortening during a twitch on the intracellular calcium transient in myocardium is unknown. Accordingly, in the present study we developed an iterative laser-diffraction feedback system that allowed for the accurate control of central-segment sarcomere length and simultaneous measurement of iontophoretically injected fura 2 fluorescence in isolated cardiac trabeculae. We compared fura 2 fluorescence signals recorded during regular twitches with twitches in which central sarcomere length (SL) was held constant by feedback control ("SL clamp" twitches). We found that uncontrolled sarcomere shortening was associated with a significant (P = 0.005) increase in the peak of the calcium transient and that the amount of this increase was directly correlated to the extent of central-segment sarcomere shortening (r2 = 0.92; P < 0.01). The time course of the calcium transient, however, was unaffected by the mode of contraction (P = 0.64). These findings have important implications for the interpretation of studies of myocardial calcium handling in which uncontrolled sarcomere shortening takes place during the twitch.
分离的心肌标本存在受损末端顺应性问题，这使得在肌肉整体长度保持恒定的收缩过程中，中央肌节能够大幅缩短。单收缩期间不受控制的肌节缩短对心肌细胞内钙瞬变的影响尚不清楚。因此，在本研究中，我们开发了一种迭代激光衍射反馈系统，该系统能够精确控制中央节段肌节长度，并同时测量分离的心脏小梁中离子导入的fura 2荧光。我们比较了在常规单收缩期间记录的fura 2荧光信号与通过反馈控制使中央肌节长度（SL）保持恒定的单收缩（“SL钳制”单收缩）期间记录的信号。我们发现，不受控制的肌节缩短与钙瞬变峰值显著（P = 0.005）增加有关，且这种增加的量与中央节段肌节缩短程度直接相关（r2 = 0.92；P < 0.01）。然而，钙瞬变的时间进程不受收缩模式的影响（P = 0.64）。这些发现对于解释在单收缩期间发生不受控制的肌节缩短的心肌钙处理研究具有重要意义。
