Tameyasu T
Department of Physiology, St. Mariana University School of Medicine, Kawasaki, Japan.
Jpn J Physiol. 1994;44(2):167-80. doi: 10.2170/jjphysiol.44.167.
Characteristics of velocity and extent of unloaded contraction were examined at a cellular and a sarcomere level in isolated rat ventricular myocytes both during an electrically-triggered twitch and a contraction wave which occurred spontaneously at an end of the myocyte and propagated toward the other end. Both the velocity and extent of shortening examined at the cellular level in the triggered twitch were independent of the length and width of the myocyte. Among the myocytes isolated separately from the right ventricle and the inner and outer layers of the left ventricle, no differences were observed in any of their length and width, the velocity and extent of shortening. The extent of shortening examined at the sarcomere level was independent of the sarcomere length (SL) before the contraction in both the triggered twitch and the spontaneous contraction in the range of the SL examined (1.6-2.1 microns). The shortening velocity decreased as a decrease of the SL in the triggered twitch at both the cellular and sarcomere levels, while independent of the SL in the spontaneous contraction as examined at the sarcomere level. On the assumption that the shortening velocity reflects the rate of increase of myoplasmic free Ca2+ concentration ([Ca2+]in) and therefore the rate of Ca2+ release from the sarcoplasmic reticulum (SR), the above result suggests that the rate of the SR Ca2+ release is dependent on the SL before the activation in the electrically-triggered, action potential-mediated twitch, while independent of the SL in the spontaneous contraction without development of any action potential.
在分离的大鼠心室肌细胞中，于细胞水平和肌节水平研究了无负荷收缩的速度和程度，观察对象包括电触发的单收缩以及在肌细胞一端自发出现并向另一端传播的收缩波。在电触发单收缩中，细胞水平检测到的缩短速度和程度均与肌细胞的长度和宽度无关。在分别从右心室以及左心室内外层分离得到的肌细胞中，其长度、宽度、缩短速度和程度均未观察到差异。在所检测的肌节长度范围（1.6 - 2.1微米）内，肌节水平检测到的缩短程度在电触发单收缩和自发收缩中均与收缩前的肌节长度（SL）无关。在细胞和肌节水平，电触发单收缩中的缩短速度随SL的减小而降低，而在肌节水平检测的自发收缩中，缩短速度与SL无关。假设缩短速度反映了肌浆游离Ca2+浓度（[Ca2+]in）的增加速率，进而反映了肌浆网（SR）释放Ca2+的速率，上述结果表明，在电触发的、动作电位介导的单收缩中，SR释放Ca2+的速率取决于激活前的SL，而在无任何动作电位产生的自发收缩中，SR释放Ca2+的速率与SL无关。
