Griffiths P J, Duchateau J J, Maeda Y, Potter J D, Ashley C C
University Laboratory of Physiology, Oxford, UK.
Pflugers Arch. 1990 Feb;415(5):554-65. doi: 10.1007/BF02583506.
Intact muscle fibres from Balanus nubilus develop tensions of up to 600 kN.m-2 during electrical stimulation. The rise of tension occurs with a half-time (177 ms at 12 degrees C) about fivefold longer than that of tetanised frog muscle at the same temperature. The response of myofibrillar bundles to a rapid stretch resembles that of frog muscle but has a yo value (i.e. the size of an instantaneous release necessary to just discharge tension) which is ca. 2.5 times smaller, and phase 2 of the tension transient (the "quick phase") occurs at a rate comparable to that of frog muscle. In contrast, the ATPase activity (0.018 mmoles.kg wet weight-1.s-1) of this preparation and its maximum shortening velocity (0.15-0.16 muscle lengths.s-1) are both at least fivefold slower than frog muscle. These findings can be accounted for by a cross-bridge cycle in barnacle muscle in which events prior and subsequent to the tension generating step(s) occur at a rate at least fivefold slower than comparable steps in frog muscle, but the step(s) associated with tension development occur at similar rates in the two preparations. Since the rate of mechanical relaxation in barnacle muscle is modified in the presence of intracellular calcium buffers and by depolarisation-induced elevation of the free calcium during the relaxation phase, it is proposed that the time course of relaxation is not determined exclusively by the kinetics of the cross-bridge cycle, but is also dependent on the free calcium concentration during relaxation.
来自巨藤壶的完整肌纤维在电刺激过程中可产生高达600 kN·m⁻²的张力。张力的上升出现的半衰期（12℃时为177毫秒）比相同温度下强直收缩的青蛙肌肉的半衰期长约五倍。肌原纤维束对快速拉伸的反应与青蛙肌肉相似，但具有一个yo值（即刚好消除张力所需的瞬时释放大小），该值约小2.5倍，并且张力瞬变的第二阶段（“快速阶段”）以与青蛙肌肉相当的速率发生。相比之下，该制剂的ATP酶活性（0.018毫摩尔·千克湿重⁻¹·秒⁻¹）及其最大缩短速度（0.15 - 0.16肌肉长度·秒⁻¹）都比青蛙肌肉至少慢五倍。这些发现可以通过藤壶肌肉中的横桥循环来解释，其中在产生张力步骤之前和之后的事件发生速率比青蛙肌肉中相应步骤至少慢五倍，但与张力发展相关的步骤在两种制剂中以相似的速率发生。由于藤壶肌肉的机械松弛速率在细胞内钙缓冲剂存在下以及在松弛阶段通过去极化诱导的游离钙升高而发生改变，因此有人提出松弛的时间进程并非仅由横桥循环的动力学决定，还取决于松弛过程中的游离钙浓度。
