Kier W M, Schachat F H
Department of Biology, University of North Carolina, Chapel Hill 27599-3280.
J Exp Biol. 1992 Jul;168:41-56. doi: 10.1242/jeb.168.1.41.
The myofilament protein compositions of muscle fibres from the transverse muscle mass of the tentacles and the transverse muscle mass of the arms of the loliginid squid Sepioteuthis lessoniana were compared. These two muscle masses are distinct types, differing in their ultrastructural and behavioural properties. The transverse muscle of the tentacles consists of specialized muscle fibres that exhibit cross-striation and unusually short sarcomeres and thick filaments. The transverse muscle of the arms consists of obliquely striated muscle fibres that are typical of cephalopod skeletal muscle in general. The specialization of the tentacle muscle results in a high shortening speed and reflects its role in creating rapid elongation of the tentacles during prey capture. Comparison of samples of myofilament preparations of the two muscle fibre types using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and peptide mapping of myosin heavy chains from the two muscle fibre types, however, showed little evidence of differences in contractile protein isoforms. Thus, specialization for high shortening speed appears to have occurred primarily through changes in the dimensions and arrangement of the myofilament lattice, rather than through changes in biochemistry. The thick filament core protein paramyosin was tentatively identified in the squid muscle fibres. This protein was less abundant in the short thick filament cross-striated tentacle muscle cells than in the obliquely striated arm cells.
对莱氏拟乌贼触须横向肌肉块和腕部横向肌肉块的肌纤维肌丝蛋白组成进行了比较。这两块肌肉属于不同类型，在超微结构和行为特性方面存在差异。触须的横向肌肉由呈现横纹且肌节和粗肌丝异常短的特化肌纤维组成。腕部的横向肌肉由一般典型的头足类骨骼肌斜纹肌纤维组成。触须肌肉的特化导致其具有较高的缩短速度，这反映了它在捕食过程中使触须快速伸长所起的作用。然而，使用十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS-PAGE）对这两种肌纤维类型的肌丝制剂样品进行比较，以及对这两种肌纤维类型的肌球蛋白重链进行肽谱分析，几乎没有发现收缩蛋白异构体存在差异的证据。因此，高缩短速度的特化似乎主要是通过肌丝晶格尺寸和排列的变化而发生的，而不是通过生物化学变化。在鱿鱼肌纤维中初步鉴定出了粗肌丝核心蛋白原肌球蛋白。这种蛋白在短粗肌丝横纹的触须肌细胞中比在斜纹的腕部肌细胞中含量少。
