Moore R L, Persechini A
Department of Medicine, Pennsylvania State University, Hershey 17033.
J Cell Physiol. 1990 May;143(2):257-62. doi: 10.1002/jcp.1041430209.
The effect of changes in muscle length on post-tetanic isometric twitch tension potentiation and myosin P-light chain phosphorylation was studied at 23 degrees C in the mouse extensor digitorum longus muscle. The length-tension relationship was determined for the same muscles after a 30 min period of quiescence and between 30 s and 3 min after a 1.5 s tetanus at L0. Isometric twitch tension is increased at all muscle lengths after the tetanus; however, the fractional increase in twitch tension rises from 0.2 at L0 to a maximum of 0.3 at 1.2 L0. The fractional increase in twitch tension measured at any fixed muscle length is constant between 30 s and 3 min post-tetanus. P-light chain phosphorylation remains constant between 30 s and 3 min post-tetanus followed by a slow decline to basal values. Under fixed length conditions, there is linear relationship between the relative magnitude of the twitch tension and the extent of P-light chain phosphorylation. Net myosin phosphorylation measured after a 1.5 s tetanus at 1.23 L0 is 35% less than that obtained under the same conditions at L0. Thus, contraction-induced phosphorylation of P-light chain decreases with increased muscle length and post-tetanic potentiation at a constant level of P-light chain phosphorylation increases with increasing muscle length. These observations may be consistent with alterations in the sarcoplasmic Ca2+ ion transient as the muscle is lengthened.
在23摄氏度下，研究了小鼠趾长伸肌肌肉长度变化对强直后等长收缩抽搐张力增强和肌球蛋白P轻链磷酸化的影响。在30分钟静止期后以及在L0处进行1.5秒强直收缩后30秒至3分钟之间，测定了相同肌肉的长度 - 张力关系。强直收缩后，所有肌肉长度的等长收缩抽搐张力均增加；然而，抽搐张力的分数增加从L0处的0.2上升至1.2L0处的最大值0.3。在强直收缩后30秒至3分钟之间，在任何固定肌肉长度下测量的抽搐张力分数增加是恒定的。P轻链磷酸化在强直收缩后30秒至3分钟之间保持恒定，随后缓慢下降至基础值。在固定长度条件下，抽搐张力的相对大小与P轻链磷酸化程度之间存在线性关系。在1.23L0处进行1.5秒强直收缩后测得的净肌球蛋白磷酸化比在相同条件下L0处获得的值少35％。因此，收缩诱导的P轻链磷酸化随着肌肉长度增加而降低，并且在恒定的P轻链磷酸化水平下，强直后增强随着肌肉长度增加而增加。这些观察结果可能与肌肉拉长时肌浆Ca2+离子瞬变的改变一致。
