许多蛇吞下大型猎物,这个过程需要下颌骨的未融合尖端的大位移和连接它们的软组织的被动拉伸。在这些条件下,颌间肌肉高度伸展,但随后恢复正常功能。在我们在蛇中观察到的高度拉伸的情况下,肌节长度(SL)增加了其静息值(SL0)的210%,肌动蛋白和肌球蛋白丝不再重叠。肌原纤维脱落,三联征对齐被破坏。被动恢复后,SL恢复到82%SL0,产生了双重叠的肌动蛋白丝区域。恢复需要细胞内肌动蛋白丝的反冲,用于重新排列肌原纤维的弹性细胞骨架成分,和肌肉激活。由于折叠的末端肌腱原纤维的伸展,整个肌肉的伸展超过了肌节,细胞外弹性蛋白的拉伸和肌纤维的独立滑移。因此,蛇下颌间肌提供了一个独特的模型,说明如何修改脊椎动物骨骼肌的基本组成部分以实现极大的延展性。
Many snakes swallow large prey whole, and this process requires large displacements of the unfused tips of the mandibles and passive stretching of the soft tissues connecting them. Under these conditions, the intermandibular muscles are highly stretched but subsequently recover normal function. In the highly stretched condition we observed in snakes, sarcomere length (SL) increased 210% its resting value (SL0), and actin and myosin filaments no longer overlapped. Myofibrils fell out of register and triad alignment was disrupted. Following passive recovery, SLs returned to 82% SL0, creating a region of double-overlapping actin filaments. Recovery required recoil of intracellular titin filaments, elastic cytoskeletal components for realigning myofibrils, and muscle activation. Stretch of whole muscles exceeded that of sarcomeres as a result of extension of folded terminal tendon fibrils, stretching of extracellular elastin and independent slippage of muscle fibers. Snake intermandibular muscles thus provide a unique model of how basic components of vertebrate skeletal muscle can be modified to permit extreme extensibility.