School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, West Yorkshire LS2 9JT, UK.
J Exp Biol. 2022 Dec 1;225(23). doi: 10.1242/jeb.244977. Epub 2022 Dec 15.
The circular muscles surrounding the mantle cavity of European cuttlefish (Sepia officinalis) generate the mechanical power to compress the cavity, forcing a jet of water out of the funnel, propelling the animal during jet propulsion swimming. During ontogeny, jetting frequency decreases in adults compared with juveniles, and this is expected to be reflected in the contractile properties of the locomotory muscles. To develop greater insight into how the locomotion of these animals is powered during ontogeny, we determined the mechanical properties of bundles of muscle fascicles during isometric, isotonic and cyclic length changes in vitro, at two life stages: juveniles and adults. The twitch kinetics were faster in juveniles than in adults (twitch rise time 257 ms compared with 371 ms; half-twitch relaxation 257 ms compared with 677 ms in juveniles and adults, respectively); however, twitch and tetanic stress, the maximum velocity of shortening and curvature of the force-velocity relationship did not differ. Under cyclic conditions, net power exhibited an inverted U-shaped relationship with cycle frequency in both juveniles and adults; the frequency at which maximum net power was achieved was shifted to lower cycle frequencies with increased maturity, which is consistent with the slower contraction and relaxation kinetics in adults compared with juveniles. The cycle frequency at which peak power was achieved during cyclical contractions in vitro was found to match that seen in vivo in juveniles, suggesting power is being maximised during jet propulsion swimming.
欧洲乌贼（Sepia officinalis）的套膜腔周围的环行肌肉产生压缩套膜腔的机械力，迫使一股水流从漏斗中喷出，从而在射流推进游泳中推动动物。在个体发育过程中，与幼体相比，成体的射流频率降低，这预计会反映在运动肌肉的收缩特性上。为了更深入地了解这些动物在个体发育过程中的运动是如何产生动力的，我们在两个生命阶段（幼体和成体）下，在体外的等长、等张和循环长度变化中，确定了肌肉束纤维的机械特性。与成体相比，幼体的抽搐动力学更快（抽搐上升时间 257ms 比 371ms；半抽搐松弛时间 257ms 比成体的 677ms）；然而，抽搐和强直应力、最大缩短速度和力-速度关系的曲率没有差异。在循环条件下，净功率与幼体和成体的循环频率呈倒 U 形关系；最大净功率出现的频率随着成熟度的增加而向较低的循环频率转移，这与成体比幼体收缩和松弛动力学更慢的情况一致。在体外周期性收缩中达到峰值功率的循环频率与幼体在体内观察到的频率相匹配，这表明在射流推进游泳中正在实现最大功率。
