Reid S K, Kennedy J M, Shimizu N, Stewart A, Vrbova G, Zak R
Department of Medicine, University of Chicago, IL 60637.
Biochem J. 1989 Jun 1;260(2):449-54. doi: 10.1042/bj2600449.
The slow tonic anterior latissimus dorsi (ALD) muscle of the chicken contains two isomyosins, namely SM-1 and SM-2. The proportions of the two isoforms change with age, SM-2 expression increasing at the expense of SM-1. Applying a load on the wing increases the rate and extent of SM-1 replacement. Here we have demonstrated that decreasing the load by removal of the distal portion of the wing in 1-week-old chickens had an effect opposite to that of overloading in that it slowed muscle growth and the rate of SM-1 elimination. Experimental unloading of muscles previously weighted for 1 or 3 weeks slowed the growth rate of muscles, with consequent regression of relative hypertrophy; however, it did not lead to the reexpression of SM-1 myosin. This indicates that the overload-induced changes in myosin expression are not readily reversible. Nerve section produced unexpected results, in that it advanced the normal developmental shift in myosin expression toward predominance of the SM-2 isoform, similar to the effect of muscle overload.
鸡的慢张力背阔肌前肌（ALD）含有两种异肌球蛋白，即SM-1和SM-2。这两种同工型的比例随年龄变化，SM-2表达增加，而SM-1表达减少。给翅膀施加负荷会增加SM-1替代的速率和程度。在此我们证明，通过切除1周龄鸡翅膀的远端部分来减轻负荷，其效果与过载相反，即减缓了肌肉生长和SM-1消除的速率。对先前称重1周或3周的肌肉进行实验性卸载，减缓了肌肉的生长速率，导致相对肥大消退；然而，这并未导致SM-1肌球蛋白的重新表达。这表明过载诱导的肌球蛋白表达变化不易逆转。神经切断产生了意想不到的结果，即它加速了肌球蛋白表达向SM-2同工型占主导的正常发育转变，类似于肌肉过载的效果。
